One document matched: draft-moskowitz-hip-rfc5201-bis-02.xml
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<rfc docName="draft-moskowitz-hip-rfc5201-bis-02" category="std" obsoletes="5201" ipr="pre5378Trust200902">
<front>
<title abbrev="Host Identity Protocol">
Host Identity Protocol</title>
<author initials="R." surname="Moskowitz"
fullname="Robert Moskowitz" role="editor">
<organization abbrev="ICSAlabs">ICSA labs, An Independent Division of Verizon Business
</organization>
<address>
<postal>
<street>1000 Bent Creek Blvd, Suite 200</street>
<city>Mechanicsburg</city>
<region>PA</region>
<country>USA</country>
</postal>
<email>robert.moskowitz@icsalabs.com</email>
</address>
</author>
<author initials="P." surname="Jokela"
fullname="Petri Jokela">
<organization>Ericsson Research NomadicLab</organization>
<address>
<postal>
<street />
<city>JORVAS</city>
<code>FIN-02420</code>
<country>FINLAND</country>
</postal>
<phone>+358 9 299 1</phone>
<email>petri.jokela@nomadiclab.com</email>
</address>
</author>
<author initials="T." surname="Henderson"
fullname="Thomas R. Henderson">
<organization>The Boeing Company</organization>
<address>
<postal>
<street>P.O. Box 3707</street>
<city>Seattle</city>
<region>WA</region>
<country>USA</country>
</postal>
<email>thomas.r.henderson@boeing.com</email>
</address>
</author>
<author initials="T." surname="Heer"
fullname="Tobias Heer">
<organization>RWTH Aachen University, Distributed Systems Group</organization>
<address>
<postal>
<street>Ahornstrasse 55</street>
<city>Aachen</city>
<code>52062</code>
<country>Germany</country>
</postal>
<email>heer@cs.rwth-aachen.de</email>
<uri>http://ds.cs.rwth-aachen.de/members/heer</uri>
</address>
</author>
<date month="July" year="2010" />
<area>Internet</area>
<keyword>HIP</keyword>
<abstract>
<t>
This document specifies the details of the Host Identity
Protocol (HIP). HIP allows consenting hosts to securely
establish and maintain shared IP-layer state, allowing
separation of the identifier and locator roles of IP addresses,
thereby enabling continuity of communications across IP address
changes. HIP is based on a SIGMA-compliant Diffie-Hellman key
exchange, using public key identifiers from a new Host Identity
namespace for mutual peer authentication. The protocol is
designed to be resistant to denial-of-service (DoS) and
man-in-the-middle (MitM) attacks. When used together with
another suitable security protocol, such as the Encapsulated
Security Payload (ESP), it provides integrity protection and
optional encryption for upper-layer protocols, such as TCP and
UDP.
</t>
<t>
This document obsoletes RFC 5201 and addresses the concerns
raised by the IESG, particularly that of crypto agility. It
also incorporates lessons learned from the implementations of
RFC 5201.
</t>
</abstract>
</front>
<middle>
<section title="Introduction">
<t>
This memo specifies the details of the Host Identity Protocol
(HIP). A high-level description of the protocol and the
underlying architectural thinking is available in the separate
<xref target="rfc4423-bis">HIP architecture description</xref>.
Briefly, the HIP architecture proposes an alternative to the
dual use of IP addresses as "locators" (routing labels) and
"identifiers" (endpoint, or host, identifiers). In HIP, public
cryptographic keys, of a public/private key pair, are used as
Host Identifiers, to which higher layer protocols are bound
instead of an IP address. By using public keys (and their
representations) as host identifiers, dynamic changes to IP
address sets can be directly authenticated between hosts, and
if desired, strong authentication between hosts at the TCP/IP
stack level can be obtained.
</t>
<t>
This memo specifies the base HIP protocol ("base exchange")
used between hosts to establish an IP-layer communications
context, called HIP association, prior to communications. It
also defines a packet format and procedures for updating an
active HIP association. Other elements of the HIP architecture
are specified in other documents, such as.
<list style='symbols'>
<t>
"Using the Encapsulating Security Payload (ESP) Transport
Format with the Host Identity Protocol (HIP)" <xref
target="RFC5202" />: how to use the Encapsulating Security
Payload (ESP) for integrity protection and optional
encryption
</t>
<t>
"End-Host Mobility and Multihoming with the Host Identity
Protocol" <xref target="RFC5206" />: how to support
mobility and multihoming in HIP
</t>
<t>
"Host Identity Protocol (HIP) Domain Name System (DNS)
Extensions" <xref target="RFC5205" />: how to extend DNS to
contain Host Identity information
</t>
<t>
"Host Identity Protocol (HIP) Rendezvous Extension" <xref
target="RFC5204" />: using a rendezvous mechanism to
contact mobile HIP hosts
</t>
</list>
</t>
<section title="A New Namespace and Identifiers">
<t>
The Host Identity Protocol introduces a new namespace, the
Host Identity namespace. Some ramifications of this new
namespace are explained in the HIP architecture description
<xref target="rfc4423-bis" />.
</t>
<t>
There are two main representations of the Host Identity, the
full Host Identifier (HI) and the Host Identity Tag (HIT).
The HI is a public key and directly represents the Identity.
Since there are different public key algorithms that can be
used with different key lengths, the HI is not good for use
as a packet identifier, or as an index into the various
operational tables needed to support HIP. Consequently, a
hash of the HI, the Host Identity Tag (HIT), becomes the
operational representation. It is 128 bits long and is used
in the HIP payloads and to index the corresponding state in
the end hosts. The HIT has an important security property in
that it is self-certifying (see <xref target="HI" />).
</t>
</section>
<section title="The HIP Base Exchange (BEX)">
<t>
The HIP base exchange is a two-party cryptographic protocol
used to establish communications context between hosts. The
base exchange is a SIGMA-compliant <xref target="KRA03" />
four-packet exchange. The first party is called the
Initiator and the second party the Responder. The
four-packet design helps to make HIP DoS resilient. The
protocol exchanges Diffie-Hellman keys in the 2nd and 3rd
packets, and authenticates the parties in the 3rd and 4th
packets. Additionally, the Responder starts a puzzle
exchange in the 2nd packet, with the Initiator completing it
in the 3rd packet before the Responder stores any state from
the exchange.
</t>
<t>
The exchange can use the Diffie-Hellman output to encrypt the
Host Identity of the Initiator in the 3rd packet (although
Aura, et al., <xref target="AUR03" /> notes that such
operation may interfere with packet-inspecting middleboxes),
or the Host Identity may instead be sent unencrypted. The
Responder's Host Identity is not protected. It should be
noted, however, that both the Initiator's and the Responder's
HITs are transported as such (in cleartext) in the packets,
allowing an eavesdropper with a priori knowledge about the
parties to verify their identities.
</t>
<t>
Data packets start to flow after the 4th packet. The 3rd and
4th HIP packets may carry a data payload in the future.
However, the details of this may be defined later.
</t>
<t>
An existing HIP association can be updated using the update
mechanism defined in this document, and when the association
is no longer needed, it can be closed using the defined
closing mechanism.
</t>
<t>
Finally, HIP is designed as an end-to-end authentication and
key establishment protocol, to be used with Encapsulated
Security Payload (ESP) <xref target="RFC5202" /> and other
end-to-end security protocols. The base protocol does not
cover all the fine-grained policy control found in Internet
Key Exchange (IKE) <xref target="RFC4306" /> that allows IKE
to support complex gateway policies. Thus, HIP is not a
replacement for IKE.
</t>
</section>
<section title="Memo Structure">
<t>
The rest of this memo is structured as follows. <xref
target="terms" /> defines the central keywords, notation, and
terms used throughout the rest of the document. <xref
target="HI" /> defines the structure of the Host Identity and
its various representations. <xref target="proto_overview"
/> gives an overview of the HIP base exchange protocol.
Sections <xref target="sec-param-tlv" format="counter" /> and
<xref target="packet_processing" format="counter" /> define
the detail packet formats and rules for packet processing.
Finally, Sections <xref target="sec-policy" format="counter"/>,
<xref target="sec-considerations" format="counter" />,
and <xref target="iana" format="counter" /> discuss policy,
security, and IANA considerations, respectively.
</t>
</section>
</section>
<section anchor="terms" title="Terms and Definitions">
<section title="Requirements Terminology">
<t>
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described
in <xref target="RFC2119">RFC 2119</xref>.
</t>
</section>
<section anchor="notation" title="Notation">
<t>
<list style="hanging">
<t hangText="[x] ">
indicates that x is optional.
</t>
<t hangText="{x} ">
indicates that x is encrypted.
</t>
<t hangText="X(y) ">
indicates that y is a parameter of X.
` </t>
<t hangText="<x>i ">
indicates that x exists i times.
</t>
<t hangText="--> ">
signifies "Initiator to Responder" communication
(requests).
</t>
<t hangText="<-- ">
signifies "Responder to Initiator" communication
(replies).
</t>
<t hangText="| ">
signifies concatenation of information-- e.g., X | Y is the
concatenation of X with Y.
</t>
<t hangText="Ltrunc (H(x), K) ">
denotes the lowest order K bits of the result
of the hash function H on the input x.
</t>
</list>
</t>
</section>
<section title="Definitions">
<t>
<list style="hanging">
<t hangText="Host Identity (HI)">
The Host Identity is the public key of a signature algorithm
and represents the identity of the host. In HIP, a host
proves its identity by creating a signature with the
private key belonging to its HI (c.f. <xref
target="HI" />).
</t>
<t hangText="Host Identity Tag (HIT)">
The Host Identity Tag is a shorthand for the HI in IPv6
format. It is generated by hashing the HI (c.f. <xref
target="HIT" />).
</t>
<t hangText="HIT Suite:">
A HIT Suite groups all cryptographic algorithms that are
required to generate and use an HI and its HIT. In
particular, these algorithms are: 1) the public key
signature algorithm and 2) the hash function, 3) the
truncation (c.f. <xref target="hit-suites" />).
</t>
<t hangText="Responder's HIT Hash Algorithm (RHASH): ">
The Hash algorithm used for various hash calculations in
this document. The algorithm is the same as is used to
generate the Responder's HIT. The RHASH is the hash
function defined by the HIT Suite of the Responder's HIT
(c.f. <xref target="hit-suites" />).
</t>
</list>
</t>
</section>
</section>
<section anchor="HI" title="Host Identifier (HI) and Its Structure">
<t>
In this section, the properties of the Host Identifier and Host
Identifier Tag are discussed, and the exact format for them is
defined. In HIP, the public key of an asymmetric key pair is
used as the Host Identifier (HI). Correspondingly, the host
itself is defined as the entity that holds the private key from
the key pair. See the HIP architecture specification <xref
target="rfc4423-bis" /> for more details about the difference
between an identity and the corresponding identifier.
</t>
<t>
HIP implementations MUST support the Rivest Shamir Adelman
(RSA) <xref target="RFC3110" /> public key algorithm, and
SHOULD support the Digital Signature Algorithm (DSA) <xref
target="RFC2536" /> algorithms, and Elliptic Curve Digital
Signature Algorithm (ECDSA) <xref target="host-id" />, ECDSA
description; other algorithms MAY be supported.
</t>
<t>
A hashed encoding of the HI, the Host Identity Tag (HIT),
is used in protocols to represent the Host Identity. The
HIT is 128 bits long and has the following three key properties:
i) it is the same length as an IPv6 address and can be used
in address-sized fields in APIs and protocols, ii) it is
self-certifying (i.e., given a HIT, it is computationally
hard to find a Host Identity key that matches the HIT), and
iii) the probability of HIT collision between two hosts is
very low, hence, it is infeasible for an attacker to find a
collision with a HIT that is in use. For details on the
security properties of the HIT see <xref target="rfc4423-bis"
/>.
<!--TH: Make sure that the HIT security is discussed
appropriately in RFC4423-bis. -->
</t>
<t>
The structure of the HIT is defined in <xref
target="RFC4843-bis" />. The HIT consists of three parts:
first, an IANA assigned prefix to distinguish it from other
IPv6 addresses. Second, a four-bit encoding of the algorithms
that were used for generating the HI and the hashed
representation of HI. Third, a 96-bit hashed representation of
the Host Identity. The encoding of the ORCHID generation
algorithm and the exact algorithm for generating the hashed
representation is specified in <xref target="hit-suites" />.
</t>
<t>
Carrying HIs and HITs in the header of user data packets would
increase the overhead of packets. Thus, it is not expected
that they are carried in every packet, but other methods are
used to map the data packets to the corresponding HIs. In some
cases, this makes it possible to use HIP without any additional
headers in the user data packets. For example, if ESP is used
to protect data traffic, the Security Parameter Index (SPI)
carried in the ESP header can be used to map the encrypted data
packet to the correct HIP association.
</t>
<section anchor="HIT" title="Host Identity Tag (HIT)">
<t>
The Host Identity Tag is a 128-bit value -- a hashed encoding
of the Host Identifier. There are two advantages of using a
hashed encoding over the actual Host Identity public key in
protocols. Firstly, its fixed length makes for easier
protocol coding and also better manages the packet size cost
of this technology. Secondly, it presents a consistent
format to the protocol whatever underlying identity
technology is used.
</t>
<t>
<xref target="RFC4843-bis">RFC 4843-bis</xref> specifies
128-bit hash-based identifiers, called Overlay Routable
Cryptographic Hash Identifiers (ORCHIDs). Their prefix,
allocated from the IPv6 address block, is defined in <xref
target="RFC4843-bis" />. The Host Identity Tag is a type of
ORCHID.
</t>
<t>
This document extends <xref target="RFC5201" /> with measures
to support crypto agility. One of these measures is to allow
for different hash functions for creating a HIT. HIT Suites
group sets of algorithms that are required to generate and
use a particular HIT. The Suites are encoded in HIT Suite
IDs. These HIT Suite IDs are transmitted in the ORCHID
Generation Algorithm field in the ORCHID. The HIT Suite ID in
the OGA field enables a hosts tell from another host's HIT,
whether it can successfully establish a HIP association with
that host.
</t>
</section>
<section title="Generating a HIT from an HI" anchor="gener_hit">
<t>
The HIT MUST be generated according to the ORCHID generation
method described in <xref target="RFC4843-bis" /> using a
context ID value of 0xF0EF F02F BFF4 3D0F E793 0C3C 6E61 74EA
(this tag value has been generated randomly by the editor of
this specification), and an input that encodes the Host
Identity field (see <xref target="host-id" />) present in a
HIP payload packet. The class of hash function, signature
algorithm, and the algorithm used for generating the HIT from
the HI depends on the HIT Suite (see <xref
target="hit-suites" />) and is indicated by the four bits of
the Orchid Generation Algorithm (OGA) field in the ORCHID.
Currently, truncated <xref
target="FIPS.95-1.1993">SHA-1</xref> and truncated <xref
target="FIPS.180-2.2002">SHA-256</xref> are defined as hashes
for generating a HIT.
</t>
<t>
For Identities that are either RSA, Digital Signature
Algorithm (DSA), or Elliptic Curve DSA (ECDSA) public keys,
the ORCHID input consists of the public key encoding as
specified in the corresponding DNSSEC documents, taking the
algorithm-specific portion of the RDATA part of the KEY RR.
There are currently only two defined public key algorithms:
RSA/SHA-1 and DSA. Hence, either of the following applies:
<list style="empty">
<t>
The RSA public key is encoded as defined in <xref
target="RFC3110" /> Section 2, taking the exponent length
(e_len), exponent (e), and modulus (n) fields
concatenated. The length (n_len) of the modulus (n) can
be determined from the total HI Length and the preceding
HI fields including the exponent (e). Thus, the data
that serves as input for the HIT generation has the same
length as the HI. The fields MUST be encoded in network
byte order, as defined in <xref target="RFC3110" />.
</t>
<t>
The DSA public key is encoded as defined in <xref
target="RFC2536" /> Section 2, taking the fields T, Q, P,
G, and Y, concatenated. Thus, the data to be hashed is 1
+ 20 + 3 * 64 + 3 * 8 * T octets long, where T is the
size parameter as defined in <xref target="RFC2536" />.
The size parameter T, affecting the field lengths, MUST
be selected as the minimum value that is long enough to
accommodate P, G, and Y. The fields MUST be encoded
in network byte order, as defined in <xref
target="RFC2536" />.
</t>
<t>
The ECDSA public key is encoded as defined in <xref
target="fundamental-ecc" /> Section 4.2 and 6.
<!--TH: check ECC text for completeness. -->
</t>
</list>
</t>
<t>
In <xref target="app_generhit" />, the public key encoding
process is illustrated using pseudo-code.
</t>
</section>
</section>
<section anchor="proto_overview" title="Protocol Overview">
<t>
The following material is an overview of the HIP protocol
operation, and does not contain all details of the packet
formats or the packet processing steps. Sections <xref
target="sec-param-tlv" format="counter" /> and <xref
target="packet_processing" format="counter" /> describe in more
detail the packet formats and packet processing steps,
respectively, and are normative in case of any conflicts with
this section.
</t>
<t>
The protocol number 139 has been assigned by IANA to the Host
Identity Protocol.
</t>
<t>
The <xref target="ssec-payload">HIP payload</xref> header could
be carried in every IP datagram. However, since HIP headers
are relatively large (40 bytes), it is desirable to 'compress'
the HIP header so that the HIP header only occurs in control
packets used to establish or change HIP association state. The
actual method for header 'compression' and for matching data
packets with existing HIP associations (if any) is defined in
separate documents, describing transport formats and methods.
All HIP implementations MUST implement, at minimum, the ESP
transport format for HIP <xref target="RFC5202" />.
</t>
<section anchor="hip-base-exch" title="Creating a HIP Association">
<t>
By definition, the system initiating a HIP exchange is the
Initiator, and the peer is the Responder. This distinction
is forgotten once the base exchange completes, and either
party can become the Initiator in future communications.
</t>
<t>
The HIP base exchange serves to manage the establishment of
state between an Initiator and a Responder. The first
packet, I1, initiates the exchange, and the last three
packets, R1, I2, and R2, constitute an authenticated
Diffie-Hellman <xref target="DIF76" /> key exchange for
session key generation. In the first two packets, the hosts
agree on a set of cryptographic identifiers and algorithms
that then are used in and after the exchange. During the
Diffie-Hellman key exchange, a piece of keying material is
generated. The HIP association keys are drawn from this
keying material. If other cryptographic keys are needed,
e.g., to be used with ESP, they are expected to be drawn from
the same keying material.
</t>
<t>
The Initiator first sends a trigger packet, I1, to the
Responder. The packet contains the HIT of the Initiator and
possibly the HIT of the Responder, if it is known. Moreover,
the I1 packet initializes the negotiation of the
Diffie-Hellman group that is used for generating the keying
material. Therefore, the I1 contains a list of Diffie Hellman
Group IDs supported by the Initiator. Note that in some
cases it may be possible to replace this trigger packet by
some other form of a trigger, in which case the protocol
starts with the Responder sending the R1 packet. In such
cases, another mechanism to convey the Initiator's supported
DH Groups (e.g., by using a default group) must be specified.
</t>
<t>
The second packet, R1, starts the actual authenticated
Diffie-Hellman exchange. It contains a puzzle -- a
cryptographic challenge that the Initiator must solve before
continuing the exchange. The level of difficulty of the
puzzle can be adjusted based on level of trust with the
Initiator, current load, or other factors. In addition, the
R1 contains the Responder's Diffie-Hellman parameter and
lists of cryptographic algorithms supported by the Responder.
Based on these lists, the Initiator can continue, abort, or
restart the base exchange with a different selection of
cryptographic algorithms. The R1 packet contains a signature
that covers selected parts of the message. Some fields are
left outside the signature to support pre-created R1s.
</t>
<t>
In the I2 packet, the Initiator must display the solution to
the received puzzle. Without a correct solution, the I2
message is discarded. The I2 also contains a Diffie-Hellman
parameter that carries needed information for the Responder.
The packet is signed by the sender.
</t>
<t>
The R2 packet acknowledges the receipt of the I2 and
finalizes the base exchange. The packet is signed.
</t>
<t>
The base exchange is illustrated below. The term "key"
refers to the Host Identity public key, and "sig" represents
a signature using such a key. The packets contain other
parameters not shown in this figure.
</t>
<figure>
<artwork>
Initiator Responder
I1: DH list
-------------------------->
select precomputed R1
R1: puzzle, DH, key, sig
<-------------------------
check sig remain stateless
solve puzzle
I2: solution, DH, {key}, sig
-------------------------->
compute DH check puzzle
check sig
R2: sig
<--------------------------
check sig compute DH
</artwork>
</figure>
<section anchor="hip-cookie" title="HIP Puzzle Mechanism">
<t>
The purpose of the HIP puzzle mechanism is to protect the
Responder from a number of denial-of-service threats. It
allows the Responder to delay state creation until
receiving I2. Furthermore, the puzzle allows the Responder
to use a fairly cheap calculation to check that the
Initiator is "sincere" in the sense that it has churned CPU
cycles in solving the puzzle.
</t>
<t>
The puzzle mechanism has been explicitly designed to give
space for various implementation options. It allows a
Responder implementation to completely delay
session-specific state creation until a valid I2 is
received. In such a case, a correctly formatted I2 can be
rejected only once the Responder has checked its validity
by computing one hash function. On the other hand, the
design also allows a Responder implementation to keep state
about received I1s, and match the received I2s against the
state, thereby allowing the implementation to avoid the
computational cost of the hash function. The drawback of
this latter approach is the requirement of creating state.
Finally, it also allows an implementation to use other
combinations of the space-saving and computation-saving
mechanisms.
</t>
<t>
The Responder can remain stateless and drop most spoofed I2s
because puzzle calculation is based on the Initiator's Host
Identity Tag. The idea is that the Responder has a (perhaps
varying) number of pre-calculated R1 packets, and it selects
one of these based on the information carried in I1. When
the Responder then later receives I2, it can verify that
the puzzle has been solved using the Initiator's HIT. This
makes it impractical for the attacker to first exchange one
I1/R1, and then generate a large number of spoofed I2s that
seemingly come from different HITs. The method does not
protect from an attacker that uses fixed HITs, though.
Against such an attacker a viable approach may be to create
a piece of local state, and remember that the puzzle check
has previously failed. See <xref target="resp-cookie" />
for one possible implementation. Implementations SHOULD
include sufficient randomness to the algorithm so that
algorithmic complexity attacks become impossible <xref
target="CRO03" />.
</t>
<t>
The Responder can set the puzzle difficulty for Initiator,
based on its level of trust of the Initiator. Because the
puzzle is not included in the signature calculation, the
Responder can use pre-calculated R1 packets and include the
puzzle just before sending the R1 to the Initiator. The
Responder SHOULD use heuristics to determine when it is
under a denial-of-service attack, and set the puzzle
difficulty value K appropriately; see below.
</t>
</section>
<section title="Puzzle Exchange" anchor="puzzle_exchange">
<t>
The Responder starts the puzzle exchange when it receives
an I1. The Responder supplies a random number I, and
requires the Initiator to find a number J. To select
a proper J, the Initiator must create the concatenation of
I, the HITs of the parties, and J, and take a hash over
this concatenation using the RHASH algorithm. The lowest
order K bits of the result MUST be zeros. The value K sets
the difficulty of the puzzle.
</t>
<t>
To generate a proper number J, the Initiator will have to
generate a number of Js until one produces the hash target
of zeros. The Initiator SHOULD give up after exceeding the
puzzle lifetime in the PUZZLE parameter (<xref
target="sec-puzzle" />). The Responder needs to re-create
the concatenation of I, the HITs, and the provided J, and
compute the hash once to prove that the Initiator did its
assigned task.
</t>
<t>
To prevent precomputation attacks, the Responder MUST
select the number I in such a way that the Initiator cannot
guess it. Furthermore, the construction MUST allow the
Responder to verify that the value I was indeed selected by
it and not by the Initiator. See <xref
target="resp-cookie" /> for an example on how to implement
this.
</t>
<t>
Using the Opaque data field in an ECHO_REQUEST_SIGNED
(<xref target="sec-echo-request-signed" />) or in an
ECHO_REQUEST_UNSIGNED parameter (<xref
target="sec-echo-request-unsigned" />), the Responder can
include some data in R1 that the Initiator must copy
unmodified in the corresponding I2 packet. The Responder
can generate the Opaque data in various ways; e.g., using
encryption or hashing with some secret, the sent I, and
possibly other related data. Using the same secret, the
received I (from the I2), and the other related data (if
any), the Receiver can verify that it has itself sent the I
to the Initiator. The Responder MUST periodically change
such a used secret.
</t>
<t>
It is RECOMMENDED that the Responder generates a new puzzle
and new R1s once every few minutes. Furthermore, it is
RECOMMENDED that the Responder remembers an old puzzle at
least Lifetime seconds after the puzzle has been
deprecated. These time values guarantee that the puzzle is
valid for at least Lifetime and at most 2*Lifetime seconds.
This limits the usability that an old, solved puzzle has to
an attacker.
</t>
<t>
NOTE: The protocol developers explicitly considered whether
R1 should include a timestamp in order to protect the
Initiator from replay attacks. The decision was to NOT
include a timestamp.
</t>
<t>
NOTE: The protocol developers explicitly considered whether
a memory bound function should be used for the puzzle
instead of a CPU-bound function. The decision was not to
use memory-bound functions. At the time of the decision,
the idea of memory-bound functions was relatively new and
their IPR status were unknown. Once there is more
experience about memory-bound functions and once their IPR
status is better known, it may be reasonable to reconsider
this decision.
<!--DONE TH: maybe the time for reconsideration has come -->
<!--DONE RGM Bring it up on the list, and we can file an issue. -->
<!--TH: There were no concrete proposals nor any strong
arguments for other puzzles on the list. I will keep
this comment open for future considerations (e.g., in
the document crafting session in Maastricht,)-->
</t>
</section>
<section anchor="auth_dh"
title="Authenticated Diffie-Hellman Protocol with DH Group
Negotiation">
<t>
The packets R1, I2, and R2 implement a standard
authenticated Diffie-Hellman exchange. The Responder sends
one of its public Diffie-Hellman keys and its public
authentication key, i.e., its Host Identity, in R1. The
signature in R1 allows the Initiator to verify that the R1
has been once generated by the Responder. However, since
it is precomputed and therefore does not cover
association-specific information in the I1 packet, it does
not protect from replay attacks.
</t>
<t>
Before the actual authenticated Diffie-Hellman exchange,
the Initiator expresses its preference regarding its choice
of the DH groups in the I1 packet. The preference is
expressed as a sorted list of DH Group IDs. The I1 packet
is not protected by a signature. Therefore, this list is
sent in an unauthenticated way to avoid costly computations
for processing the I1 packet on the Responder's side. Based
on the preferences of the Initiator, the Responder sends an
R1 packet containing its most suitable public DH value. It
also attaches a list of its own preferences to the R1 to
convey the basis for the DH group selection to the
Initiator.
<!--TH: I removed the following optimization for now:
Note that the R1 packet may be precomputed. Hence,
only the hashes of the DH values supported by the Responder
are covered by the PK signature in the R1 packet while the
actual DH public value is not covered by the PK signature.
-->
<!--TH: Now we have to ask ourselves if we really want to
have full flexibility in the DH key exchange so that
the Responder can support a large number of DH group
IDs. In this case we need something like signed hashes
to have more flexibility in the R1. Otherwise we could
leave things as they are and accept that the Responder
may have to precalculate several R1 packets with
different public DH values. -->
</t>
<t>
If none of the DH Group IDs in the I1 is supported by the
Responder, the Responder selects the DH Group most
suitable for it regardless of the Initiator's preference.
It then sends the R1 containing this DH Group and its list
of supported DH Group IDs to the Initiator.
</t>
<t>
When the Initiator receives an R1, it gets one of the
Responder's public Diffie-Hellman values and the list of DH
Group IDs supported by the Responder. This list is covered
by the signature in the R1 packet to avoid forgery. The
Initiator compares the Group ID of the public DH value in
the R1 packet to the list of supported DH Group IDs in the
R1 packets and to its own preferences expressed in the list
of supported DH Group IDs. The Initiator continues the BEX
only if the Group ID of the public DH value of the
Responder matches the preferences of both Initiator and
Responder. Otherwise, the communication is subject of a
downgrade attack and the Initiator must restart the key
exchange with a new I1 packet or must abort the key
exchange. If the Responder's choice of the DH Group is not
supported by the Initiator, the Initiator may abort the
handshake or send a new I1 with a different list of
supported DH Groups. However, the Initiator MUST verify the
signature of the R1 packet before restarting or aborting
the handshake. It MUST silently ignore the R1 packet if the
signature is not valid.
</t>
<t>
If the preferences regarding the DH Group ID match, the
Initiator computes the Diffie-Hellman session key (Kij).
It creates a HIP association using keying material from the
session key (see <xref target="keymat" />), and may use the
association to encrypt its public authentication key, i.e.,
Host Identity. The resulting I2 contains the Initiator's
Diffie-Hellman key and its (optionally encrypted) public
authentication key. The signature in I2 covers all of the
packet.
</t>
<t>
The Responder extracts the Initiator Diffie-Hellman public
key from the I2, computes the Diffie-Hellman session key,
creates a corresponding HIP association, and decrypts the
Initiator's public authentication key. It can then verify
the signature using the authentication key.
</t>
<t>
The final message, R2, is needed to protect the Initiator
from replay attacks.
</t>
</section>
<section anchor="hip-replay" title="HIP Replay Protection">
<t>
The HIP protocol includes the following mechanisms to
protect against malicious replays. Responders are
protected against replays of I1 packets by virtue of the
stateless response to I1s with presigned R1 messages.
Initiators are protected against R1 replays by a
monotonically increasing "R1 generation counter" included
in the R1. Responders are protected against replays or
false I2s by the puzzle mechanism (<xref
target="hip-cookie" /> above), and optional use of opaque
data. Hosts are protected against replays to R2s and
UPDATEs by use of a less expensive HMAC verification
preceding HIP signature verification.
</t>
<t>
The R1 generation counter is a monotonically increasing
64-bit counter that may be initialized to any value. The
scope of the counter MAY be system-wide but SHOULD be per
Host Identity, if there is more than one local host
identity. The value of this counter SHOULD be kept across
system reboots and invocations of the HIP base exchange.
This counter indicates the current generation of puzzles.
Implementations MUST accept puzzles from the current
generation and MAY accept puzzles from earlier generations.
A system's local counter MUST be incremented at least as
often as every time old R1s cease to be valid, and SHOULD
never be decremented, lest the host expose its peers to the
replay of previously generated, higher numbered R1s. The
R1 counter SHOULD NOT roll over.
</t>
<t>
A host may receive more than one R1, either due to sending
multiple I1s (<xref target="multi-i1" />) or due to a
replay of an old R1. When sending multiple I1s, an
Initiator SHOULD wait for a small amount of time (a
reasonable time may be 2 * expected RTT) after the first R1
reception to allow possibly multiple R1s to arrive, and it
SHOULD respond to an R1 among the set with the largest R1
generation counter. If an Initiator is processing an R1 or
has already sent an I2 (still waiting for R2) and it
receives another R1 with a larger R1 generation counter, it
MAY elect to restart R1 processing with the fresher R1, as
if it were the first R1 to arrive.
</t>
<t>
Upon conclusion of an active HIP association with another
host, the R1 generation counter associated with the peer
host SHOULD be flushed. A local policy MAY override the
default flushing of R1 counters on a per-HIT basis. The
reason for recommending the flushing of this counter is
that there may be hosts where the R1 generation counter
(occasionally) decreases; e.g., due to hardware failure.
</t>
</section>
<section title="Refusing a HIP Exchange">
<t>
A HIP-aware host may choose not to accept a HIP exchange.
If the host's policy is to only be an Initiator, it should
begin its own HIP exchange. A host MAY choose to have such
a policy since only the Initiator's HI is protected in the
exchange. There is a risk of a race condition if each
host's policy is to only be an Initiator, at which point
the HIP exchange will fail.
</t>
<t>
If the host's policy does not permit it to enter into a HIP
exchange with the Initiator, it should send an ICMP
'Destination Unreachable, Administratively Prohibited'
message. A more complex HIP packet is not used here as it
actually opens up more potential DoS attacks than a simple
ICMP message.
</t>
</section>
<section title="Aborting a HIP Exchange">
<t>
Two HIP hosts may encounter situations in which they cannot
complete a HIP exchange because of insufficient suport for
cryptographic algorithms, in particular the HIT Suites and
DH Groups. After receiving the R1 packet, the Initiator can
determine whether the Responder supports the required
cryptographic operations to successfully establish a HIP
association. The Initiator can abort the BEX silently after
receiving an R1 packet that indicates an unsupported set of
algorithms. The specific conditions are described below.
</t>
<t>
The R1 packet contains a signed list of HIT Suite IDs
supported by the Responder. Therefore, the Initiator can
determine whether its source HIT is supported by the
Responder. If the HIT Suite ID of the Initiator's HIT is
not contained in the list of HIT Suites, the Initiator MAY
abort the handshake silently or MAY restart the handshake
with a new I1 packet that contains a source HIT supported
by the Responder.
</t>
<t>
During the Handshake, the Initiator and the Responder agree
on a DH Group. The Responder selects the DH Group and its
DH public value in the R1 based on the list of DH Suite IDs
in the I1 packet. If the responder supports none of the DH
Groups selected by the Initiator, the Responder selects an
arbitrary DH and replies an R1 containing its list of
supported DH Group IDs. In this case, the Initiator will
receive an R1 packet containing the DH public value for an
unsupported DH Group and the Responder's DH Group list in
the signed part of the R1 packet. At this point, the
Initiator MAY abort the handshake or MAY restart the
handshake by sending a new I1 containing a selection of DH
Group IDs that is supported by the Responder.
</t>
</section>
<section title="HIP Downgrade Protection">
<t>
In a downgrade attack, an attacker manipulates the packets
of an Initiator and/or a Responder to unnoticeably
influence the result of the cryptographic negotiations in
the BEX to its favor. As a result, the victims select
weaker cryptographic algorithms than they would have
without the attacker's interference. Downgrade attacks can
only be successful if these are not detected by the victims
and the victims assume a secure communication channel.
</t>
<t>
In HIP, almost all packet parameters related to
cryptographic negotiations are covered by signatures. These
parameters cannot be directly manipulated in a downgrade
attack without invalidating the signature. However, signed
packets can be subject to replay attacks. In such a replay
attack, the attacker could use an old BEX packet with an
outdated selection of cryptographic algorithms and replay
it instead of a more recent packet with a collection of
stronger cryptographic algorithms. Signed packets that
could be subject to this replay attack are the R1 and I2
packet. However, replayed R1 and I2 packets cannot be used
to successfully establish a HIP BEX because these packets
also contain the public DH values of the Initiator and the
Responder. Old DH values from replayed packet will lead to
invalid keying material and mismatching shared secrets.
</t>
<t>
In contrast to the first version of HIP <xref
target="RFC5201"/>, this version begins the negotiation of
the DH Groups already in the first BEX packet, the I1. The
I1 is, by intention, not protected by a signature to avoid
CPU-intensive cryptographic operations for processing
floods of I1s. Hence, the list of DH Group IDs in the I1 is
vulnerable to forgery and manipulation. To thwart an
unnoticed manipulation of the I1 packet, the Responder
chooses the DH Group deterministically and includes its own
list of DH Group IDs in the signed part of the R1 packet.
The Initiator can detect an attempted downgrade attack by
comparing the list of DH Group IDs in the R1 packet to its
own preferences in the I1. If the choice of the DH Group
in the R1 packet does not equal the best match of the two
lists, the Initiator can conclude that its list in the I1
was altered by an attacker. In this case, the Initiator can
restart or abort the BEX. As mentioned before, the
detection of the downgrade attack is sufficient to prevent
it.
</t>
</section>
<section anchor="op_mode" title="HIP Opportunistic Mode">
<t>
It is possible to initiate a HIP negotiation even if the
Responder's HI (and HIT) is unknown. In this case, the
connection initializing I1 packet contains NULL (all zeros)
as the destination HIT. This kind of connection setup is
called opportunistic mode.
</t>
<t>
The Responder may have multiple HITs due to multiple
supported HIT Suites. Since the Responder's HIT Suite is
not determined by the destination HIT of the I1 packet, the
Responder can freely select a HIT of any HIT Suite. The
complete set of HIT Suites supported by the Initiator is
not known to the Responder. Therefore, the Responder SHOULD
use a Responder HIT of the same HIT Suite as the
Initiator's HIT because this HIT Suite is obviously
supported by the Initiator. If the Responder selects a
different HIT that is not supported by the Initiator, the
Initiator MAY restart the BEX with an I1 packet with a
source HIT that is contained in the list of the Responder's
HIT Suites in the R1 packet.
</t>
<t> Note that the Initiator cannot verify the signature of
the R1 packet if the Responder's HIT Suite is not supported.
Therefore, the Initiator MUST treat R1 packets with
unsupported Responder HITs as potentially forged and MUST NOT
use any parameters from the unverified R1 besides the HIT
Suite List. Moreover, an Initiator that uses a unverified HIT
Suite List to determine a possible source HIT from an R1
packet MUST verify that the HIT_SUITE_LIST in the first
unverified R1 packet matches the HIT_SUITE_LIST in the second
R1 packet for which the Initiator supports the signature
algorithm. The Initiator MUST restart the BEX with a new I1
packet with a source HIT mentioned in the verifiable R1 if
the two lists do not match to mitigate downgrade attacks.
</t>
<t>
There are both security and API issues involved with the
opportunistic mode.
</t>
<t>
Given that the Responder's HI is not known by the
Initiator, there must be suitable API calls that allow the
Initiator to request, directly or indirectly, that the
underlying kernel initiate the HIP base exchange solely
based on locators. The Responder's HI will be tentatively
available in the R1 packet, and in an authenticated form
once the R2 packet has been received and verified. Hence,
it could be communicated to the application via new API
mechanisms. However, with a backwards-compatible API the
application sees only the locators used for the initial
contact. Depending on the desired semantics of the API,
this can raise the following issues:
</t>
<t>
<list style="symbols">
<t>
The actual locators may later change if an UPDATE
message is used, even if from the API perspective the
session still appears to be between specific locators.
The locator update is still secure, however, and the
session is still between the same nodes.
</t>
<t>
Different sessions between the same locators may result
in connections to different nodes, if the
implementation no longer remembers which identifier the
peer had in another session. This is possible when the
peer's locator has changed for legitimate reasons or
when an attacker pretends to be a node that has the
peer's locator. Therefore, when using opportunistic
mode, HIP MUST NOT place any expectation that the
peer's HI returned in the R1 message matches any HI
previously seen from that address.
<vspace blankLines='1' />
If the HIP implementation and application do not have
the same understanding of what constitutes a session,
this may even happen within the same session. For
instance, an implementation may not know when HIP state
can be purged for UDP-based applications.
</t>
<t>
As with all HIP exchanges, the handling of
locator-based or interface-based policy is unclear for
opportunistic mode HIP. An application may make a
connection to a specific locator because the
application has knowledge of the security properties
along the network to that locator. If one of the nodes
moves and the locators are updated, these security
properties may not be maintained. Depending on the
security policy of the application, this may be a
problem. This is an area of ongoing study. As an
example, there is work to create an API that
applications can use to specify their security
requirements in a similar context <xref
target="btns-c-api" />.
</t>
</list>
</t>
<t>
In addition, the following security considerations apply.
The generation counter mechanism will be less efficient in
protecting against replays of the R1 packet, given that the
Responder can choose a replay that uses any HI, not just
the one given in the I1 packet.
</t>
<t>
More importantly, the opportunistic exchange is vulnerable
to man-in-the-middle attacks, because the Initiator does
not have any public key information about the peer. To
assess the impacts of this vulnerability, we compare it to
vulnerabilities in current, non-HIP-capable
communications.
</t>
<t>
An attacker on the path between the two peers can insert
itself as a man-in-the-middle by providing its own
identifier to the Initiator and then initiating another HIP
session towards the Responder. For this to be possible, the
Initiator must employ opportunistic mode, and the Responder
must be configured to accept a connection from any
HIP-enabled node.
</t>
<t>
An attacker outside the path will be unable to do so, given
that it cannot respond to the messages in the base
exchange.
</t>
<t>
These properties are characteristic also of communications
in the current Internet. A client contacting a server
without employing end-to-end security may find itself
talking to the server via a man-in-the-middle, assuming
again that the server is willing to talk to anyone.
</t>
<t>
If end-to-end security is in place, then the worst that can
happen in both the opportunistic HIP and normal IP cases is
denial-of-service; an entity on the path can disrupt
communications, but will be unable to insert itself as a
man-in-the-middle.
</t>
<t>
However, once the opportunistic exchange has successfully
completed, HIP provides integrity protection and
confidentiality for the communications, and can securely
change the locators of the endpoints.
</t>
<t>
As a result, it is believed that the HIP opportunistic mode
is at least as secure as current IP.
</t>
</section>
</section>
<section title="Updating a HIP Association">
<t>
A HIP association between two hosts may need to be updated
over time. Examples include the need to rekey expiring user
data security associations, add new security associations, or
change IP addresses associated with hosts. The UPDATE packet
is used for those and other similar purposes. This document
only specifies the UPDATE packet format and basic processing
rules, with mandatory parameters. The actual usage is
defined in separate specifications.
</t>
<t>
HIP provides a general purpose UPDATE packet, which can carry
multiple HIP parameters, for updating the HIP state between
two peers. The UPDATE mechanism has the following
properties:
<list>
<t>
UPDATE messages carry a monotonically increasing sequence
number and are explicitly acknowledged by the peer. Lost
UPDATEs or acknowledgments may be recovered via
retransmission. Multiple UPDATE messages may be
outstanding under certain circumstances.
</t>
<t>
UPDATE is protected by both HIP_MAC and HIP_SIGNATURE
parameters, since processing UPDATE signatures alone is a
potential DoS attack against intermediate systems.
</t>
<t>
UPDATE packets are explicitly acknowledged by the use of
an acknowledgment parameter that echoes an individual
sequence number received from the peer. A single UPDATE
packet may contain both a sequence number and one or more
acknowledgment numbers (i.e., piggybacked
acknowledgment(s) for the peer's UPDATE).
</t>
</list>
</t>
<t>
The UPDATE packet is defined in <xref target="UPDATE" />.
</t>
</section>
<section anchor="error_proc" title="Error Processing">
<t>
HIP error processing behavior depends on whether or not there
exists an active HIP association. In general, if a HIP
association exists between the sender and receiver of a
packet causing an error condition, the receiver SHOULD
respond with a NOTIFY packet. On the other hand, if there
are no existing HIP associations between the sender and
receiver, or the receiver cannot reasonably determine the
identity of the sender, the receiver MAY respond with a
suitable ICMP message; see <xref target="ICMP" /> for more
details.
</t>
<t>
The HIP protocol and state machine is designed to recover
from one of the parties crashing and losing its state. The
following scenarios describe the main use cases covered by
the design.
<list>
<t>No prior state between the two systems.
<list>
<t>
The system with data to send is the Initiator. The
process follows the standard four-packet base
exchange, establishing the HIP association.
</t>
</list>
</t>
<t>
The system with data to send has no state with the
receiver, but the receiver has a residual HIP
association.
<list>
<t>
The system with data to send is the Initiator. The
Initiator acts as in no prior state, sending I1 and
getting R1. When the Responder receives a valid I2,
the old association is 'discovered' and deleted, and
the new association is established.
</t>
</list>
</t>
<t>
The system with data to send has a HIP association, but
the receiver does not.
<list>
<t>
The system sends data on the outbound user data
security association. The receiver 'detects' the
situation when it receives a user data packet that it
cannot match to any HIP association. The receiving
host MUST discard this packet.
</t>
<t>
Optionally, the receiving host MAY send an ICMP
packet, with the type Parameter Problem, to inform
the sender that the HIP association does not exist
(see Section 5.4), and it MAY initiate a new HIP
negotiation. However, responding with these optional
mechanisms is implementation or policy dependent.
</t>
</list>
</t>
</list>
</t>
</section>
<section anchor="state-machine" title="HIP State Machine">
<t>
The HIP protocol itself has little state. In the HIP base
exchange, there is an Initiator and a Responder. Once the
security associations (SAs) are established, this distinction
is lost. If the HIP state needs to be re-established, the
controlling parameters are which peer still has state and
which has a datagram to send to its peer. The following
state machine attempts to capture these processes.
</t>
<t>
The state machine is presented in a single system view,
representing either an Initiator or a Responder. There is
not a complete overlap of processing logic here and in the
packet definitions. Both are needed to completely implement
HIP.
</t>
<t>
This document extends the state machine defined in <xref
target="RFC5201" /> and introduces a restart option to allow
for the negotiation of cryptographic algorithms. The only
change to the previous state machine is a transition from
state I1-SENT to I1-SENT - the restart option. An Initiator
is required to restart the HIP exchange if the Responder does
not support the HIT Suite of the Initiator. In this case, the
Initiator restarts the HIP exchange by sending a new I1
packet with a source HIT supported by the Responder.
</t>
<t>
Implementors must understand that the state machine, as
described here, is informational. Specific implementations
are free to implement the actual functions differently.
<xref target="packet_processing" /> describes the packet
processing rules in more detail. This state machine focuses
on the HIP I1, R1, I2, and R2 packets only. Other states may
be introduced by mechanisms in other specifications (such as
mobility and multihoming).
</t>
<section title="Timespan Definitions">
<t>
<list style="hanging">
<t hangText="Unused Association Lifetime (UAL): ">
Implementation-specific time for which, if no packet is
sent or received for this time interval, a host MAY
begin to tear down an active association.
</t>
<t hangText="Maximum Segment Lifetime (MSL): ">
Maximum time that a TCP segment is expected to spend in
the network.
</t>
<t hangText="Exchange Complete (EC): ">
Time that the host spends at the R2-SENT before it
moves to ESTABLISHED state. The time is n * I2
retransmission timeout, where n is about
I2_RETRIES_MAX.
</t>
</list>
</t>
</section>
<section anchor="states" title="HIP States">
<?rfc compact="no"?>
<texttable align="left" title="HIP States" anchor="table_states">
<ttcol width="30%" align="left">State</ttcol>
<ttcol align="left">Explanation</ttcol>
<c>UNASSOCIATED</c><c>State machine start</c>
<c>I1-SENT</c><c> Initiating base exchange </c>
<c>I2-SENT</c><c> Waiting to complete base exchange </c>
<c>R2-SENT</c><c> Waiting to complete base exchange </c>
<c>ESTABLISHED</c><c> HIP association established </c>
<c>CLOSING</c><c> HIP association closing, no data can be sent</c>
<c>CLOSED</c><c> HIP association closed, no data can be sent</c>
<c>E-FAILED</c><c> HIP exchange failed </c>
</texttable>
<?rfc compact="yes"?>
</section>
<section title="HIP State Processes">
<?rfc compact="no"?>
<texttable align="left" title="UNASSOCIATED - Start state" anchor="table_unassociated">
<preamble>System behavior in state UNASSOCIATED, <xref
target="table_unassociated" />.</preamble>
<ttcol width="30%" align="left">Trigger</ttcol>
<ttcol align="left">Action</ttcol>
<c>User data to send, requiring a new HIP association</c>
<c>Send I1 and go to I1-SENT</c>
<c>Receive I1</c>
<c>Send R1 and stay at UNASSOCIATED</c>
<c>Receive I2, process</c>
<c>If successful, send R2 and go to R2-SENT</c>
<c></c>
<c>If fail, stay at UNASSOCIATED</c>
<c>Receive user data for unknown HIP association</c>
<c>Optionally send ICMP as defined in <xref target="ICMP" />
and stay at UNASSOCIATED</c>
<c>Receive CLOSE</c>
<c>Optionally send ICMP Parameter Problem and stay at
UNASSOCIATED</c>
<c>Receive ANYOTHER</c>
<c>Drop and stay at UNASSOCIATED</c>
</texttable>
<texttable align="left" title="I1-SENT - Initiating HIP" anchor="table_i1sent">
<preamble>System behavior in state I1-SENT, <xref
target="table_i1sent" />.</preamble>
<ttcol width="30%" align="left">Trigger</ttcol>
<ttcol align="left">Action</ttcol>
<c>Receive I1</c>
<c>If the local HIT is smaller than the peer HIT, drop I1 and
stay at I1-SENT</c>
<c></c>
<c>If the local HIT is greater than the peer HIT, send R1
and stay at I1_SENT</c>
<c>Receive I2, process</c>
<c>If successful, send R2 and go to R2-SENT</c>
<c></c>
<c>If fail, stay at I1-SENT</c>
<c>Receive R1, process</c>
<c>If HIT Suite of own HIT is not supported by the peer, select supported own HIT,
send I1 and stay at I1-SENT</c>
<c></c>
<c>If successful, send I2 and go to I2-SENT</c>
<c></c>
<c>If fail, stay at I1-SENT</c>
<c>Receive ANYOTHER</c>
<c>Drop and stay at I1-SENT</c>
<c>Timeout, increment timeout counter</c>
<c>If counter is less than I1_RETRIES_MAX, send I1 and stay at I1-SENT</c>
<c></c>
<c>If counter is greater than I1_RETRIES_MAX, go to E-FAILED</c>
</texttable>
<texttable align="left" title="I2-SENT - Waiting to finish HIP" anchor="table_i2sent">
<preamble>System behavior in state I2-SENT, <xref
target="table_i2sent" />.</preamble>
<ttcol width="30%" align="left">Trigger</ttcol>
<ttcol align="left">Action</ttcol>
<c>Receive I1</c>
<c>Send R1 and stay at I2-SENT</c>
<c>Receive R1, process</c>
<c>If successful, send I2 and cycle at I2-SENT</c>
<c></c>
<c>If fail, stay at I2-SENT</c>
<c>Receive I2, process</c>
<c>If successful and local HIT is smaller than the peer HIT,
drop I2 and stay at I2-SENT</c>
<c></c>
<c>If successful and local HIT is greater than the peer HIT,
send R2 and go to R2-SENT</c>
<c></c>
<c>If fail, stay at I2-SENT</c>
<c>Receive R2, process</c>
<c>If successful, go to ESTABLISHED</c>
<c></c>
<c>If fail, stay at I2-SENT</c>
<c>Receive ANYOTHER</c>
<c>Drop and stay at I2-SENT</c>
<c>Timeout, increment timeout counter</c>
<c>If counter is less than I2_RETRIES_MAX, send I2 and
stay at I2-SENT</c>
<c></c>
<c>If counter is greater than I2_RETRIES_MAX, go to E-FAILED</c>
</texttable>
<texttable align="left" title="R2-SENT - Waiting to finish HIP" anchor="table_r2sent">
<preamble>System behavior in state R2-SENT, <xref
target="table_r2sent" />.</preamble>
<ttcol width="30%" align="left">Trigger</ttcol>
<ttcol align="left">Action</ttcol>
<c>Receive I1</c>
<c>Send R1 and stay at R2-SENT</c>
<c>Receive I2, process</c>
<c>If successful, send R2 and cycle at R2-SENT</c>
<c></c>
<c>If fail, stay at R2-SENT</c>
<c>Receive R1</c>
<c>Drop and stay at R2-SENT</c>
<c>Receive R2</c>
<c>Drop and stay at R2-SENT</c>
<c>Receive data or UPDATE</c>
<c>Move to ESTABLISHED</c>
<c>Exchange Complete Timeout</c>
<c>Move to ESTABLISHED</c>
</texttable>
<texttable align="left"
title="ESTABLISHED - HIP association established"
anchor="table_established">
<preamble>System behavior in state ESTABLISHED, <xref
target="table_established" />.</preamble>
<ttcol width="30%" align="left">Trigger</ttcol>
<ttcol align="left">Action</ttcol>
<c>Receive I1</c>
<c>Send R1 and stay at ESTABLISHED</c>
<c>Receive I2, process with puzzle and possible Opaque
data verification</c>
<c>If successful, send R2, drop old HIP association,
establish a new HIP association, go to R2-SENT</c>
<c></c>
<c>If fail, stay at ESTABLISHED</c>
<c>Receive R1</c>
<c>Drop and stay at ESTABLISHED</c>
<c>Receive R2</c>
<c>Drop and stay at ESTABLISHED</c>
<c>Receive user data for HIP association</c>
<c>Process and stay at ESTABLISHED</c>
<c>No packet sent/received during UAL minutes</c>
<c>Send CLOSE and go to CLOSING</c>
<c>Receive CLOSE, process</c>
<c>If successful, send CLOSE_ACK and go to CLOSED</c>
<c></c>
<c>If fail, stay at ESTABLISHED</c>
</texttable>
<texttable align="left" title="CLOSING - HIP association has not been used for UAL minutes" anchor="table_closing">
<preamble>System behavior in state CLOSING, <xref
target="table_closing" />.</preamble>
<ttcol width="30%" align="left">Trigger</ttcol>
<ttcol align="left">Action</ttcol>
<c>User data to send, requires the creation of another incarnation
of the HIP association</c>
<c>Send I1 and stay at CLOSING</c>
<c>Receive I1</c>
<c>Send R1 and stay at CLOSING</c>
<c>Receive I2, process</c>
<c>If successful, send R2 and go to R2-SENT</c>
<c></c>
<c>If fail, stay at CLOSING</c>
<c>Receive R1, process</c>
<c>If successful, send I2 and go to I2-SENT</c>
<c></c>
<c>If fail, stay at CLOSING</c>
<c>Receive CLOSE, process</c>
<c>If successful, send CLOSE_ACK, discard state and
go to CLOSED</c>
<c></c>
<c>If fail, stay at CLOSING</c>
<c>Receive CLOSE_ACK, process</c>
<c>If successful, discard state and go to UNASSOCIATED</c>
<c></c>
<c>If fail, stay at CLOSING</c>
<c>Receive ANYOTHER</c>
<c>Drop and stay at CLOSING</c>
<c>Timeout, increment timeout sum, reset timer</c>
<c>If timeout sum is less than UAL+MSL minutes, retransmit CLOSE
and stay at CLOSING</c>
<c></c>
<c>If timeout sum is greater than UAL+MSL minutes, go
to UNASSOCIATED</c>
</texttable>
<texttable align="left" title="CLOSED - CLOSE_ACK sent, resending CLOSE_ACK if necessary"
anchor="table_closed">
<preamble>System behavior in state CLOSED, <xref
target="table_closed" />.</preamble>
<ttcol width="30%" align="left">Trigger</ttcol>
<ttcol align="left">Action</ttcol>
<c>Datagram to send, requires the creation of another incarnation
of the HIP association</c>
<c>Send I1, and stay at CLOSED</c>
<c>Receive I1</c>
<c>Send R1 and stay at CLOSED</c>
<c>Receive I2, process</c>
<c>If successful, send R2 and go to R2-SENT</c>
<c></c>
<c>If fail, stay at CLOSED</c>
<c>Receive R1, process</c>
<c>If successful, send I2 and go to I2-SENT</c>
<c></c>
<c>If fail, stay at CLOSED</c>
<c>Receive CLOSE, process</c>
<c>If successful, send CLOSE_ACK, stay at CLOSED</c>
<c></c>
<c>If fail, stay at CLOSED</c>
<c>Receive CLOSE_ACK, process</c>
<c>If successful, discard state and go to UNASSOCIATED</c>
<c></c>
<c>If fail, stay at CLOSED</c>
<c>Receive ANYOTHER</c>
<c>Drop and stay at CLOSED</c>
<c>Timeout (UAL+2MSL)</c>
<c>Discard state, and go to UNASSOCIATED</c>
</texttable>
<?rfc needLines="10"?>
<texttable align="left" title="E-FAILED - HIP failed to establish association with peer"
anchor="table_efailed">
<preamble>System behavior in state E-FAILED, <xref
target="table_efailed" />.</preamble>
<ttcol width="30%" align="left">Trigger</ttcol>
<ttcol align="left">Action</ttcol>
<c>Wait for implementation-specific time</c>
<c>Go to UNASSOCIATED. Re-negotiation is possible after moving to
UNASSOCIATED state.</c>
</texttable>
<?rfc compact="yes"?>
</section>
<section anchor="hipstates" title="Simplified HIP State Diagram">
<t>
The following diagram shows the major state transitions.
Transitions based on received packets implicitly assume that
the packets are successfully authenticated or processed.
</t>
<figure>
<artwork>
+-+ +----------------------------+
I1 received, send R1 | | | |
| v v |
Datagram to send +--------------+ I2 received, send R2 |
+---------------| UNASSOCIATED |----------------+ |
| +-+ +--------------+ | |
Send I1 | | | Alg. not supported, send I1 | |
v | v | |
+---------+ I2 received, send R2 | |
+---->| I1-SENT |---------------------------------------+ | |
| +---------+ | | |
| | +------------------------+ | | |
| | R1 received, | I2 received, send R2 | | | |
| v send I2 | v v v |
| +---------+ | +---------+ |
| +->| I2-SENT |------------+ | R2-SENT |<----+ |
| | +---------+ +---------+ | |
| | | | | |
| | | data| | |
| |receive | or| | |
| |R1, send | EC timeout| receive I2,| |
| |I2 |R2 received +--------------+ | send R2| |
| | +----------->| ESTABLISHED |<--------+ | |
| | +--------------+ | |
| | | | | receive I2, send R2 | |
| | recv+------------+ | +------------------------+ |
| | CLOSE,| | | |
| | send| No packet sent| | |
| | CLOSE_ACK| /received for | timeout | |
| | | UAL min, send | +---------+<-+ (UAL+MSL) | |
| | | CLOSE +--->| CLOSING |--+ retransmit | |
| | | +---------+ CLOSE | |
+--|------------|----------------------+| | | | | |
+------------|-----------------------+ | | +-----------------+ |
| | +-----------+ +-------------------|--+
| +-----------+ | receive CLOSE, CLOSE_ACK | |
| | | send CLOSE_ACK received or | |
| | | timeout | |
| | | (UAL+MSL) | |
| v v | |
| +--------+ receive I2, send R2 | |
+-----------------------| CLOSED |----------------------------+ |
+--------+ /-----------------------+
^ | \-------/ timeout (UAL+2MSL),
| | move to UNASSOCIATED
+-+
CLOSE received, send CLOSE_ACK
</artwork>
</figure>
</section>
</section>
<section title="User Data Considerations">
<section title="TCP and UDP Pseudo-Header Computation for User Data">
<t>
When computing TCP and UDP checksums on user data packets
that flow through sockets bound to HITs, the IPv6
pseudo-header format <xref target="RFC2460" /> MUST be
used, even if the actual addresses on the packet are IPv4
addresses. Additionally, the HITs MUST be used in the
place of the IPv6 addresses in the IPv6 pseudo-header.
Note that the pseudo-header for actual HIP payloads is
computed differently; see <xref target="ssec-crc" />.
</t>
</section>
<section title="Sending Data on HIP Packets">
<t>
A future version of this document may define how to include
user data on various HIP packets. However, currently the
HIP header is a terminal header, and not followed by any
other headers.
</t>
</section>
<section title="Transport Formats">
<t>
The actual data transmission format, used for user data
after the HIP base exchange, is not defined in this
document. Such transport formats and methods are described
in separate specifications. All HIP implementations MUST
implement, at minimum, the ESP transport format for HIP
<xref target="RFC5202" />.
</t>
</section>
<section anchor="reboot" title="Reboot, Timeout, and Restart of HIP">
<t>
Simulating a loss of state is a potential DoS attack. The
following process has been crafted to manage state recovery
without presenting a DoS opportunity.
</t>
<t>
If a host reboots or the HIP association times out, it has
lost its HIP state. If the host that lost state has a
datagram to send to the peer, it simply restarts the HIP
base exchange. After the base exchange has completed, the
Initiator can create a new payload association and start
sending data. The peer does not reset its state until it
receives a valid I2 HIP packet.
</t>
<t>
If a system receives a user data packet that cannot be
matched to any existing HIP association, it is possible
that it has lost the state and its peer has not. It MAY
send an ICMP packet with the Parameter Problem type, and
with the pointer pointing to the referred HIP-related
association information. Reacting to such traffic depends
on the implementation and the environment where the
implementation is used.
</t>
<t>
If the host, that apparently has lost its state, decides to
restart the HIP base exchange, it sends an I1 packet to the
peer. After the base exchange has been completed
successfully, the Initiator can create a new HIP
association and the peer drops its old payload associations
and creates a new
one.
</t>
</section>
</section>
<section title="Certificate Distribution">
<t>
This document does not define how to use certificates or how
to transfer them between hosts. These functions are expected
to be defined in a future specification. A parameter type
value, meant to be used for carrying certificates, is
reserved, though: CERT, Type 768; see <xref target="hippars"
/>.
</t>
</section>
</section>
<section anchor="sec-param-tlv" title="Packet Formats">
<section anchor="ssec-payload" title="Payload Format">
<t>
All HIP packets start with a fixed header.
</t>
<figure>
<artwork>
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Header Length |0| Packet Type | VER. | RES.|1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Checksum | Controls |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender's Host Identity Tag (HIT) |
| |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Receiver's Host Identity Tag (HIT) |
| |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
/ HIP Parameters /
/ /
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure>
<t>
The HIP header is logically an IPv6 extension header.
However, this document does not describe processing for Next
Header values other than decimal 59, IPPROTO_NONE, the IPv6
'no next header' value. Future documents MAY do so.
However, current implementations MUST ignore trailing data if
an unimplemented Next Header value is received.
</t>
<t>
The Header Length field contains the length of the HIP Header
and HIP parameters in 8-byte units, excluding the first 8
bytes. Since all HIP headers MUST contain the sender's and
receiver's HIT fields, the minimum value for this field is 4,
and conversely, the maximum length of the HIP Parameters
field is (255*8)-32 = 2008 bytes. Note: this sets an
additional limit for sizes of parameters included in the
Parameters field, independent of the individual parameter
maximum lengths.
</t>
<t>
The Packet Type indicates the HIP packet type. The
individual packet types are defined in the relevant sections.
If a HIP host receives a HIP packet that contains an unknown
packet type, it MUST drop the packet.
</t>
<t>
The HIP Version is four bits. The current version is 2. The
version number is expected to be incremented only if there
are incompatible changes to the protocol. Most extensions
can be handled by defining new packet types, new parameter
types, or new controls.
</t>
<t>
The following three bits are reserved for future use. They
MUST be zero when sent, and they SHOULD be ignored when
handling a received packet.
</t>
<t>
The two fixed bits in the header are reserved for potential
SHIM6 compatibility <xref target="RFC5533" />. For
implementations adhering (only) to this specification, they
MUST be set as shown when sending and MUST be ignored when
receiving. This is to ensure optimal forward compatibility.
Note that for implementations that implement other compatible
specifications in addition to this specification, the
corresponding rules may well be different. For example, in
the case that the forthcoming SHIM6 protocol happens to be
compatible with this specification, an implementation that
implements both this specification and the SHIM6 protocol may
need to check these bits in order to determine how to handle
the packet.
</t>
<t>The HIT fields are always 128 bits (16 bytes) long.</t>
<section anchor="ssec-crc" title="Checksum">
<t>
Since the checksum covers the source and destination
addresses in the IP header, it must be recomputed on
HIP-aware NAT devices.
</t>
<t>
If IPv6 is used to carry the HIP packet, the pseudo-header
<xref target="RFC2460" /> contains the source and
destination IPv6 addresses, HIP packet length in the
pseudo-header length field, a zero field, and the HIP
protocol number (see <xref target="proto_overview" />) in
the Next Header field. The length field is in bytes and
can be calculated from the HIP header length field: <spanx
style="tt">(HIP Header Length + 1) * 8</spanx>.
</t>
<t>
In case of using IPv4, the IPv4 UDP pseudo-header format
<xref target="RFC0768" /> is used. In the pseudo-header,
the source and destination addresses are those used in the
IP header, the zero field is obviously zero, the protocol
is the HIP protocol number (see <xref
target="proto_overview" />), and the length is calculated
as in the IPv6 case.
</t>
</section>
<section title="HIP Controls">
<t>
The HIP Controls section conveys information about the
structure of the packet and capabilities of the host.
</t>
<t>
The following fields have been defined:
<figure>
<artwork>
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | | | | | | | | | | | | | |A|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure>
<list style="hanging">
<t hangText="A - Anonymous: ">
If this is set, the sender's HI in this packet is
anonymous, i.e., one not listed in a directory.
Anonymous HIs SHOULD NOT be stored. This control is
set in packets R1 and/or I2. The peer receiving an
anonymous HI may choose to refuse it.
</t>
</list>
The rest of the fields are reserved for future use and MUST
be set to zero on sent packets and ignored on received
packets.
</t>
</section>
<section title="HIP Fragmentation Support">
<t>
A HIP implementation must support IP
fragmentation/reassembly. Fragment reassembly MUST be
implemented in both IPv4 and IPv6, but fragment generation
is REQUIRED to be implemented in IPv4 (IPv4 stacks and
networks will usually do this by default) and RECOMMENDED
to be implemented in IPv6. In IPv6 networks, the minimum
MTU is larger, 1280 bytes, than in IPv4 networks. The
larger MTU size is usually sufficient for most HIP packets,
and therefore fragment generation may not be needed. If a
host expects to send HIP packets that are larger than the
minimum IPv6 MTU, it MUST implement fragment generation
even for IPv6.
</t>
<t>
In IPv4 networks, HIP packets may encounter low MTUs along
their routed path. Since HIP does not provide a mechanism
to use multiple IP datagrams for a single HIP packet,
support for path MTU discovery does not bring any value to
HIP in IPv4 networks. HIP-aware NAT devices MUST perform
any IPv4 reassembly/fragmentation.
</t>
<t>
All HIP implementations have to be careful while employing
a reassembly algorithm so that the algorithm is
sufficiently resistant to DoS attacks.
</t>
<t>
Because certificate chains can cause the packet to be
fragmented and fragmentation can open implementation to
denial-of-service attacks <xref target="KAU03" />, it is
strongly recommended that the separate document specifying
the certificate usage in the HIP Base Exchange defines the
usage of "Hash and URL" formats rather than including
certificates in exchanges. With this, most problems
related to DoS attacks with fragmentation can be avoided.
</t>
</section>
</section>
<section anchor="hippars" title="HIP Parameters">
<t>
The HIP Parameters are used to carry the public key
associated with the sender's HIT, together with related
security and other information. They consist of ordered
parameters, encoded in TLV format.
</t>
<t>
The following parameter types are currently defined.
</t>
<?rfc compact="no"?>
<texttable>
<ttcol width="27%" align="left">TLV</ttcol>
<ttcol width="5%" align="left">Type</ttcol>
<ttcol width="14%" align="left">Length</ttcol>
<ttcol align="left">Data</ttcol>
<c>R1_COUNTER</c><c>128</c><c>12</c><c>System Boot Counter</c>
<c>PUZZLE</c><c>257</c><c>12</c><c>K and Random #I</c>
<c>SOLUTION</c><c>321</c><c>20</c><c>K, Random #I and puzzle
solution J</c>
<c>SEQ</c><c>385</c><c>4</c><c>Update packet ID number</c>
<c>ACK</c><c>449</c><c>variable</c><c>Update packet ID number</c>
<c>DIFFIE_HELLMAN</c><c>513</c><c>variable</c><c>public key</c>
<c>HIP_CIPHER</c><c>579</c><c>variable</c><c>HIP encryption
algorithm</c>
<c>ENCRYPTED</c><c>641</c><c>variable</c><c>Encrypted part of
I2 packet</c>
<c>HOST_ID</c><c>705</c><c>variable</c><c>Host Identity with
Fully-Qualified Domain FQDN (Name) or Network Access Identifier (NAI)</c>
<c>HIT_SUITE_LIST</c><c>715</c><c>variable</c><c>Ordered list of the HIT
suites supported by the Responder</c>
<c>CERT</c><c>768</c><c>variable</c><c>HI Certificate; used
to transfer certificates. Usage is currently not defined, but it
will be specified in a separate document once needed.</c>
<c>NOTIFICATION</c><c>832</c><c>variable</c><c>Informational
data</c>
<c>ECHO_REQUEST_SIGNED</c><c>897</c><c>variable</c><c>Opaque
data to be echoed back; under signature</c>
<c>ECHO_RESPONSE_SIGNED</c><c>961</c><c>variable</c><c>Opaque data
echoed back; under signature</c>
<c>DH_GROUP_LIST</c><c>2151</c><c>variable</c><c>Ordered list of DH
Group IDs supported by a host</c>
<c>HIP_MAC</c><c>61505</c><c>variable</c><c>HMAC-based message
authentication code, with key material from KEYMAT</c>
<c>HIP_MAC_2</c><c>61569</c><c>variable</c><c>HMAC based message
authentication code, with key material from KEYMAT.
Compared to HIP_MAC, the HOST_ID parameter is included in HIP_MAC_2
calculation.</c>
<c>HIP_SIGNATURE_2</c><c>61633</c><c>variable</c><c>Signature
of the R1 packet</c>
<c>HIP_SIGNATURE</c><c>61697</c><c>variable</c><c>Signature
of the packet</c>
<c>ECHO_REQUEST_UNSIGNED</c><c>63661</c><c>variable</c><c>Opaque
data to be echoed back; after signature</c>
<c>ECHO_RESPONSE_UNSIGNED</c><c>63425</c><c>variable</c><c>Opaque
data echoed back; after signature</c>
</texttable>
<?rfc compact="yes"?>
<t>
Because the ordering (from lowest to highest) of HIP
parameters is strictly enforced (see <xref target="tlvformat"
/>), the parameter type values for existing parameters have
been spaced to allow for future protocol extensions.
Parameters numbered between 0-1023 are used in HIP handshake
and update procedures and are covered by signatures.
Parameters numbered between 1024-2047 are reserved.
Parameters numbered between 2048-4095 are used for parameters
that are covered by a signature but may also be present in
packets without signatures. Parameters numbered between
4096 and (2^16 - 2^12) 61439 are reserved. Parameters
numbered between 61440-62463 are used for signatures and
signed MACs. Parameters numbered between 62464-63487 are
used for parameters that fall outside of the signed area of
the packet. Parameters numbered between 63488-64511 are used
for rendezvous and other relaying services. Parameters
numbered between 64512-65535 are reserved.
</t>
<section anchor="tlvformat" title="TLV Format">
<t>
The TLV-encoded parameters are described in the following
subsections. The type-field value also describes the order
of these fields in the packet, except for type values from
2048 to 4095 which are reserved for new transport forms.
The parameters MUST be included in the packet such that
their types form an increasing order. If the parameter can
exist multiple times in the packet, the type value may be
the same in consecutive parameters. If the order does not
follow this rule, the packet is considered to be malformed
and it MUST be discarded.
</t>
<t>
Parameters using type values from 2048 up to 4095 are
transport formats. Currently, one transport format is
defined: the ESP transport format <xref target="RFC5202"
/>. The order of these parameters does not follow the
order of their type value, but they are put in the packet
in order of preference. The first of the transport formats
it the most preferred, and so on.
</t>
<t>
All of the TLV parameters have a length (including Type and
Length fields), which is a multiple of 8 bytes. When
needed, padding MUST be added to the end of the parameter
so that the total length becomes a multiple of 8 bytes.
This rule ensures proper alignment of data. Any added
padding bytes MUST be zeroed by the sender, and their
values SHOULD NOT be checked by the receiver.
</t>
<t>
Consequently, the Length field indicates the length of the
Contents field (in bytes). The total length of the TLV
parameter (including Type, Length, Contents, and Padding)
is related to the Length field according to the following
formula:
</t>
<t>
Total Length = 11 + Length - (Length + 3) % 8;
</t>
<t>
where % is the modulo operator
</t>
<figure>
<artwork>
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type |C| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
/ Contents /
/ +-+-+-+-+-+-+-+-+
| | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type Type code for the parameter. 16 bits long, C-bit
being part of the Type code.
C Critical. One if this parameter is critical, and
MUST be recognized by the recipient, zero otherwise.
The C bit is considered to be a part of the Type
field. Consequently, critical parameters are always
odd and non-critical ones have an even value.
Length Length of the Contents, in bytes excluding Type,
Length, and Padding.
Contents Parameter specific, defined by Type
Padding Padding, 0-7 bytes, added if needed
</artwork>
</figure>
<t>
Critical parameters MUST be recognized by the recipient.
If a recipient encounters a critical parameter that it does
not recognize, it MUST NOT process the packet any further.
It MAY send an ICMP or NOTIFY, as defined in <xref
target="error_proc" />.
</t>
<t>
Non-critical parameters MAY be safely ignored. If a
recipient encounters a non-critical parameter that it does
not recognize, it SHOULD proceed as if the parameter was
not present in the received packet.
</t>
</section>
<section title="Defining New Parameters">
<t>
Future specifications may define new parameters as needed.
When defining new parameters, care must be taken to ensure
that the parameter type values are appropriate and leave
suitable space for other future extensions. One must
remember that the parameters MUST always be arranged in
increasing order by Type code, thereby limiting the order
of parameters (see <xref target="tlvformat" />).
</t>
<t>
The following rules must be followed when defining new
parameters.
<list style="numbers">
<t>
The low-order bit C of the Type code is used to
distinguish between critical and non-critical
parameters.
</t>
<t>
A new parameter may be critical only if an old
recipient ignoring it would cause security problems.
In general, new parameters SHOULD be defined as
non-critical, and expect a reply from the recipient.
</t>
<t>
If a system implements a new critical parameter, it
MUST provide the ability to set the associated feature
off, such that the critical parameter is not sent at
all. The configuration option must be well documented.
Implementations operating in a mode adhering to this
specification MUST disable the sending of new critical
parameters. In other words, the management interface
MUST allow vanilla standards-only mode as a default
configuration setting, and MAY allow new critical
payloads to be configured on (and off).
</t>
<t>
See <xref target="iana" /> for allocation rules
regarding Type codes.
</t>
</list>
</t>
</section>
<section anchor="r1_counter" title="R1_COUNTER">
<figure>
<artwork>
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved, 4 bytes |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| R1 generation counter, 8 bytes |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type 128
Length 12
R1 generation
counter The current generation of valid puzzles
</artwork>
</figure>
<t>
The R1_COUNTER parameter contains a 64-bit unsigned integer
in network-byte order, indicating the current generation of
valid puzzles. The sender is supposed to increment this
counter periodically. It is RECOMMENDED that the counter
value is incremented at least as often as old PUZZLE values
are deprecated so that SOLUTIONs to them are no longer
accepted.
</t>
<t>
The R1_COUNTER parameter is optional. It SHOULD be
included in the R1 (in which case, it is covered by the
signature), and if present in the R1, it MAY be echoed
(including the Reserved field verbatim) by the Initiator in
the I2.
</t>
</section>
<section anchor="sec-puzzle" title="PUZZLE">
<figure>
<artwork>
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| K, 1 byte | Lifetime | Opaque, 2 bytes |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Random #I, n bytes |
/ /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type 257
Length 4+RHASH-len/8
K K is the number of verified bits
Lifetime puzzle lifetime 2^(value-32) seconds
Opaque data set by the Responder, indexing the puzzle
Random #I random number of size RHASH-len bits
</artwork>
</figure>
<t>
Random #I is represented as a n-bit integer (where n is RHASH-len/2),
K and Lifetime as 8-bit integers, all in network byte order.
</t>
<t>
The PUZZLE parameter contains the puzzle difficulty K and a
n-bit puzzle random integer #I. The Puzzle Lifetime
indicates the time during which the puzzle solution is
valid, and sets a time limit that should not be exceeded by
the Initiator while it attempts to solve the puzzle. The
lifetime is indicated as a power of 2 using the formula
2^(Lifetime-32) seconds. A puzzle MAY be augmented with an
ECHO_REQUEST_SIGNED or an ECHO_REQUEST_UNSIGNED parameter
included in the R1; the contents of the echo request are
then echoed back in the ECHO_RESPONSE_SIGNED or in the
ECHO_RESPONSE_UNSIGNED, allowing the Responder to use the
included information as a part of its puzzle processing.
</t>
<t>
The Opaque and Random #I field are not covered by the
HIP_SIGNATURE_2 parameter.
</t>
</section>
<section title="SOLUTION">
<figure>
<artwork>
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| K, 1 byte | Reserved | Opaque, 2 bytes |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Random #I, n bytes |
/ /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Puzzle solution #J, n bytes |
/ /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type 321
Length 4 + RHASH-len/4
K K is the number of verified bits
Reserved zero when sent, ignored when received
Opaque copied unmodified from the received PUZZLE
parameter
Random #I random number of size RHASH-len bits
Puzzle solution #J random number of size RHASH-len bits
</artwork>
</figure>
<t>
Random #I and Random #J are represented as n-bit integers
(where n is RHASH-len/2), K as an 8-bit integer, all in
network byte order.
</t>
<t>
The SOLUTION parameter contains a solution to a puzzle. It
also echoes back the random difficulty K, the Opaque field,
and the puzzle integer #I.
</t>
</section>
<section anchor="diffie_hellman" title="DIFFIE_HELLMAN">
<figure>
<artwork>
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Group ID | Public Value Length | Public Value /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type 513
Length length in octets, excluding Type, Length, and
Padding
Group ID defines values for p and g
Public Value length of the following Public Value in octets
Length
Public Value the sender's public Diffie-Hellman key
</artwork>
</figure>
<t>The following Group IDs have been defined:</t>
<figure>
<artwork>
Group Value
Reserved 0
DEPRECATED 1
DEPRECATED 2
1536-bit MODP group 3 [RFC3526]
3072-bit MODP group 4 [RFC3526]
DEPRECATED 5
DEPRECATED 6
160-bit random ECP group 7 [Appendix D, draft-mcgrew-fundamental-ecc-02.txt]
256-bit random ECP group 8 [RFC4753, draft-mcgrew-fundamental-ecc-02.txt]
384-bit random ECP group 9 [RFC4753, draft-mcgrew-fundamental-ecc-02.txt]
521-bit random ECP group 10 [RFC4753, draft-mcgrew-fundamental-ecc-02.txt]
</artwork>
</figure>
<t>
The MODP Diffie-Hellman groups are defined in <xref
target="RFC3526" />. The ECDH groups 8 - 10 are defined
in <xref target="RFC4753" /> and <xref
target="fundamental-ecc" />. ECDH group 7 is covered in
<xref target="ecdh-160-group" />.
</t>
<t>
A HIP implementation MUST implement Group ID 3. The 160-bit
ECP group can be used when lower security is enough (e.g.,
web surfing) and when the equipment is not powerful enough
(e.g., some PDAs). Implementations SHOULD implement Group
IDs 4 and 8.
</t>
<!--RM will we need an appendix for ECDH 160? and is this the 'right'
lite size? -->
<t>
To avoid unnecessary failures during the base exchange, the
rest of the groups SHOULD be implemented in hosts where
resources are adequate.
</t>
</section>
<section anchor="hip_cipher" title="HIP_CIPHER">
<figure>
<artwork>
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cipher ID #1 | Cipher ID #2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cipher ID #n | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type 579
Length length in octets, excluding Type, Length, and
Padding
Cipher ID defines the cipher algorithm to be used for
encrypting parts of the HIP packet
</artwork>
</figure>
<t>
The following Cipher IDs are defined:</t>
<figure>
<artwork>
Suite ID Value
RESERVED 0
NULL-ENCRYPT 1 ([RFC2410])
AES-128-CBC 2 ([RFC3602])
3DES-CBC 3 ([RFC2451])
</artwork>
</figure>
<t>
The sender of a HIP_CIPHER parameter MUST make sure
that there are no more than six (6) Cipher IDs in one
HIP_CIPHER parameter. Conversely, a recipient MUST be
prepared to handle received transport parameters that
contain more than six Cipher IDs by accepting the first
six Cipher IDs and dropping the rest. The limited
number of transforms sets the maximum size of the
HIP_CIPHER parameter. As the default configuration,
the HIP_CIPHER parameter MUST contain at least one of
the mandatory Cipher IDs. There MAY be a configuration
option that allows the administrator to override this
default.
</t>
<t>
The Responder lists supported and desired Cipher IDs in
order of preference in the R1, up to the maximum of six
Cipher IDs. The Initiator MUST choose only one of the
corresponding Cipher IDs. That Cipher ID will be used
for generating the ENCRYPTED parameter.
</t>
<t>
Mandatory implementation: AES-CBC, NULL-ENCRYPTION is
included for testing purposes. NULL-ENCRYPTION SHOULD
NOT be configurable via the UI.
</t>
</section>
<section anchor="host-id" title="HOST_ID">
<figure>
<artwork>
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| HI Length |DI-type| DI Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Host Identity /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ | Domain Identifier /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type 705
Length length in octets, excluding Type, Length, and
Padding
HI Length length of the Host Identity in octets
DI-type type of the following Domain Identifier field
DI Length length of the FQDN or NAI in octets
Host Identity actual Host Identity
Domain Identifier the identifier of the sender
</artwork>
</figure>
<t>
The Host Identity is represented in the DNSKEY format for RSA and DSA.
For these, the Public Key field from <xref target="RFC4034">
RFC 4034</xref> is used. For ECC Host Identities this field is
defined here directly.
</t>
<figure>
<artwork>
Algorithms Values
RESERVED 0
DSA 3 [RFC2536] (RECOMMENDED)
RSA 5 [RFC3110] (REQUIRED)
ECDSA 7 [fundamental-ecc] (RECOMMENDED)
</artwork>
</figure>
<t>
For ECDSA the Host Identity is represented by the following fields:
</t>
<figure>
<artwork>
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ECC Curve | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Public Key /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
ECC Curve Curve label
Public Key Represented in Octect-string format [fundamental-ecc]
</artwork>
</figure>
<t>
Required ECC Curve values are:
</t>
<figure>
<artwork>
Curve Values
RESERVED 0
NIST-ECDSA-256 1 [RFC4754]
NIST-ECDSA-384 2 [RFC4754]
brainpoolP160r1 3 [RFC5639]
</artwork>
</figure>
<t>The following DI-types have been defined:</t>
<figure>
<artwork>
Type Value
none included 0
FQDN 1
NAI 2
FQDN Fully Qualified Domain Name, in binary format.
NAI Network Access Identifier
</artwork>
</figure>
<t>
The format for the FQDN is defined in <xref
target="RFC1035"> RFC 1035</xref> Section 3.1. The format
for NAI is defined in <xref target="RFC4282" />
</t>
<t>
If there is no Domain Identifier, i.e., the DI-type field
is zero, the DI Length field is set to zero as well.
</t>
</section>
<section anchor="hit_suite_list" title="HIT_SUITE_LIST">
<figure>
<artwork>
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ID #1 | ID #2 | ID #3 | ID #4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ID #n | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type 715
Length number of HIT Suite IDs
ID defines a HIT Suite ID supported by the host.
The list of IDs is ordered by preference of the
host. Each HIT Suite ID is one octet long. The four
higher-order bits correspond to the HIT Suite ID in
the ORCHID OGA field. The four lower-order bits are
set to 0.
</artwork>
</figure>
<t>
The ID field in the HIT_SUITE_LIST is defined as eight-bit
field opposed to the four-bit HIT Suite ID and OGA field in
the ORCHID. This difference is a measure to accommodate
larger HIT Suite IDs if the 16 available values prove
insufficient. In that case, one of the 16 values (0) will
be used to indicate that four additional bits of the ORCHID
will be used to encode the HIT Suite ID. Hence, the current
four-bit HIT Suite-IDs only use the four higher order bits
in the ID field. Future documents may define the use of the
four lower-order bits in the ID field.
^ </t>
<t>
The following HIT Suites ID are defined:</t>
<figure>
<artwork>
HIT Suite ID
RESERVED 0
RSA/DSA/SHA-1 1 (REQUIRED)
ECDSA/SHA-256 2 (RECOMMENDED)
ECDSA/SHA-384 3 (RECOMMENDED)
</artwork>
<!--TH Do we really need 1, 256 AND 384. We are using up suite IDs
much too quick. -->
<!--TH: I left the HIT Suite 0-reserved there because I think
it might be smartest to have 0 as optional growth class
instead of 15.-->
<!--RGM I do not like how many I needed so far for ECDSA...-->
</figure>
<t>
The HIT_SUITE_LIST parameter contains a list of the supported HIT
suite IDs of the Responder. The Responder sends the HIT_SUITE_LIST
in the signed part of the R1 packet. Based on the HIT_SUITE_LIST,
the Initiator can determine which source HITs are supported by the
Responder.
</t>
</section>
<section anchor="dh_group_list" title="DH_GROUP_LIST">
<figure>
<artwork>
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DH GROUP ID #1| DH GROUP ID #2| DH GROUP ID #3| DH GROUP ID #4|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DH GROUP ID #n| Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type 2151
Length number of DH Group IDs
DH GROUP ID defines a DH GROUP ID supported by the host.
The list of IDs is ordered by preference of the
host. The list of define DH Group IDs in the
DIFFIE_HELLMAN parameter. Each DH Group ID is one
octet long.
</artwork>
</figure>
<t>
The DH_GROUP_LIST parameter contains the list of supported DH
Group IDs of a host. The Initiator sends
the DH_GROUP_LIST in the I1 packet, the Responder sends it in the
signed part of the R1 packet. The DH Group IDs in the
DH_GROUP_LIST are listed in the order of their preference
of the host. DH Group IDs that are listed first are
preferred compared to the DH Group IDs listed later. The
information in the DH_GROUP_LIST allows the Responder to select
the DH group preferred by itself and the Initiator. Based on
the DH_GROUP_LIST in the R1 packet, the Initiator can determine
if the Responder has selected the best possible choice based
on the Initiator's and Responder's preferences. If the
Responder's choice differs from the best choice, the
Initiator can conclude that there was an attempted downgrade
attack.
</t>
<t>
When selecting the DH group for the DIFFIE_HELLMAN
parameter in the R1 packet, the Responder MUST select the
first DH Group ID in the Responder's DH_GROUP_LIST that is
contained in the Initiator's DH_GROUP_LIST.
</t>
</section>
<section anchor="HIP_MAC" title="HIP_MAC">
<figure>
<artwork>
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| HMAC |
/ /
/ +-------------------------------+
| | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type 61505
Length length in octets, excluding Type, Length, and
Padding
HMAC HMAC computed over the HIP packet, excluding the
HIP_MAC parameter and any following parameters, such
as HIP_SIGNATURE, HIP_SIGNATURE_2,
ECHO_REQUEST_UNSIGNED, or ECHO_RESPONSE_UNSIGNED.
The checksum field MUST be set to zero and the HIP
header length in the HIP common header MUST be
calculated not to cover any excluded parameters
when the HMAC is calculated. The size of the
HMAC is the natural size of the hash computation
output depending on the used hash function.
</artwork>
</figure>
<t>
The HMAC uses RHASH as hash algorithm. The calculation and
verification process is presented in <xref
target="hmac-processing" />.
</t>
</section>
<section anchor="HIP_MAC_2" title="HIP_MAC_2">
<t>The parameter structure is the same as in <xref
target="HIP_MAC" />. The fields are:</t>
<figure>
<artwork>
Type 61569
Length length in octets, excluding Type, Length, and
Padding
HMAC HMAC computed over the HIP packet, excluding the
HIP_MAC parameter and any following parameters such
as HIP_SIGNATURE, HIP_SIGNATURE_2,
ECHO_REQUEST_UNSIGNED, or ECHO_RESPONSE_UNSIGNED,
and including an additional sender's HOST_ID
parameter during the HMAC calculation. The
checksum field MUST be set to zero and the HIP
header length in the HIP common header MUST be
calculated not to cover any excluded parameters
when the HMAC is calculated. The size of the
HMAC is the natural size of the hash computation
output depending on the used hash function.
</artwork>
</figure>
<t>
The HMAC uses RHASH as hash algorithm. The calculation and
verification process is presented in <xref
target="hmac-processing" />.
</t>
</section>
<section anchor="hip-signature" title="HIP_SIGNATURE">
<figure>
<artwork>
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SIG alg | Signature /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type 61697
Length length in octets, excluding Type, Length, and
Padding
SIG alg signature algorithm
Signature the signature is calculated over the HIP packet,
excluding the HIP_SIGNATURE parameter and any
parameters that follow the HIP_SIGNATURE parameter.
The checksum field MUST be set to zero, and the HIP
header length in the HIP common header MUST be
calculated only to the beginning of the
HIP_SIGNATURE parameter when the signature is
calculated.
</artwork>
</figure>
<t>
The signature algorithms are defined in <xref
target="host-id" />. The signature in the Signature field
is encoded using the proper method depending on the
signature algorithm (e.g., according to <xref
target="RFC3110"/> in case of RSA/SHA-1, according to <xref
target="RFC5702" /> in case of RSA/SHA-256, according to
<xref target="RFC2536" /> in case of DSA, or according to
<xref target="fundamental-ecc" /> in case of ECDSA).
</t>
<t>
The HIP_SIGNATURE calculation and verification process is
presented in <xref target="sig-processing" />.
</t>
</section>
<section anchor="HIP_SIGNATURE_2" title="HIP_SIGNATURE_2">
<t>
The parameter structure is the same as in <xref
target="hip-signature" />. The fields are:
</t>
<figure>
<artwork>
Type 61633
Length length in octets, excluding Type, Length, and
Padding
SIG alg signature algorithm
Signature Within the R1 packet that contains the
HIP_SIGNATURE_2 parameter, the Initiator's HIT, the
checksum field, and the Opaque and Random #I fields
in the PUZZLE parameter MUST be set to zero while
computing the HIP_SIGNATURE_2 signature. Further,
the HIP packet length in the HIP header MUST be
adjusted as if the HIP_SIGNATURE_2 was not in the
packet during the signature calculation, i.e., the
HIP packet length points to the beginning of
the HIP_SIGNATURE_2 parameter during signing and
verification.
</artwork>
</figure>
<t>
Zeroing the Initiator's HIT makes it possible to create R1
packets beforehand, to minimize the effects of possible DoS
attacks. Zeroing the Random #I and Opaque fields within the
PUZZLE parameter allows these fields to be populated
dynamically on precomputed R1s.
</t>
<t>
Signature calculation and verification follows the process
in <xref target="sig-processing" />.
</t>
</section>
<section title="SEQ">
<figure>
<artwork>
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Update ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type 385
Length 4
Update ID 32-bit sequence number
</artwork>
</figure>
<t>
The Update ID is an unsigned quantity, initialized by a
host to zero upon moving to ESTABLISHED state. The Update
ID has scope within a single HIP association, and not
across multiple associations or multiple hosts. The Update
ID is incremented by one before each new UPDATE that is
sent by the host; the first UPDATE packet originated by a
host has an Update ID of 0.
</t>
</section>
<section title="ACK">
<figure>
<artwork>
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| peer Update ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type 449
Length variable (multiple of 4)
peer Update ID 32-bit sequence number corresponding to the
Update ID being ACKed.
</artwork>
</figure>
<t>
The ACK parameter includes one or more Update IDs that have
been received from the peer. The Length field identifies
the number of peer Update IDs that are present in the
parameter.
</t>
</section>
<section title="ENCRYPTED">
<figure>
<artwork>
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IV /
/ /
/ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ /
/ Encrypted data /
/ /
/ +-------------------------------+
/ | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type 641
Length length in octets, excluding Type, Length, and
Padding
Reserved zero when sent, ignored when received
IV Initialization vector, if needed, otherwise
nonexistent. The length of the IV is inferred from
the HIP_CIPHER.
Encrypted The data is encrypted using an encryption algorithm
data as defined in the HIP_CIPHER parameter.
</artwork>
</figure>
<t>
The ENCRYPTED parameter encapsulates another parameter, the
encrypted data, which holds one or more HIP parameters in
block encrypted form.
</t>
<t>
Consequently, the first fields in the encapsulated
parameter(s) are Type and Length of the first such
parameter, allowing the contents to be easily parsed after
decryption.
</t>
<t>
The field labelled "Encrypted data" consists of the output
of one or more HIP parameters concatenated together that
have been passed through an encryption algorithm. Each of
these inner parameters is padded according to the rules of
<xref target="tlvformat"/> for padding individual
parameters. As a result, the concatenated parameters will
be a block of data that is 8-byte aligned.
</t>
<t>
Some encryption algorithms require that the data to be
encrypted must be a multiple of the cipher algorithm block
size. In this case, the above block of data MUST include
additional padding, as specified by the encryption
algorithm. The size of the extra padding is selected so
that the length of the unencrypted data block is a multiple
of the cipher block size. The encryption algorithm may
specify padding bytes other than zero; for example, <xref
target="FIPS.197.2001">AES</xref> uses the PKCS5 padding
scheme (see section 6.1.1 of <xref target="RFC2898"/>) where
the remaining n bytes to fill the block each have the value
n. This yields an "unencrypted data" block that is
transformed to an "encrypted data" block by the cipher
suite. This extra padding added to the set of parameters to
satisfy the cipher block alignment rules is not counted in
HIP TLV length fields, and this extra padding should be
removed by the cipher suite upon decryption.
</t>
<t>
Note that the length of the cipher suite output may be
smaller or larger than the length of the set of parameters
to be encrypted, since the encryption process may compress
the data or add additional padding to the data.
</t>
<t>
Once this encryption process is completed, the Encrypted
data field is ready for inclusion in the Parameter. If
necessary, additional Padding for 8-byte alignment is then
added according to the rules of <xref target="tlvformat"/>.
</t>
</section>
<section anchor="notify" title="NOTIFICATION">
<t>
The NOTIFICATION parameter is used to transmit
informational data, such as error conditions and state
transitions, to a HIP peer. A NOTIFICATION parameter may
appear in the NOTIFY packet type. The use of the
NOTIFICATION parameter in other packet types is for further
study.
</t>
<figure>
<artwork>
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Notify Message Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| /
/ Notification Data /
/ +---------------+
/ | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type 832
Length length in octets, excluding Type, Length, and
Padding
Reserved zero when sent, ignored when received
Notify Message specifies the type of notification
Type
Notification informational or error data transmitted in addition
Data to the Notify Message Type. Values for this field
are type specific (see below).
Padding any Padding, if necessary, to make the parameter a
multiple of 8 bytes.
</artwork>
</figure>
<t>
Notification information can be error messages specifying
why an SA could not be established. It can also be status
data that a process managing an SA database wishes to
communicate with a peer process. The table below lists the
Notification messages and their corresponding values.
</t>
<t>
To avoid certain types of attacks, a Responder SHOULD avoid
sending a NOTIFICATION to any host with which it has not
successfully verified a puzzle solution.
</t>
<t>
Types in the range 0-16383 are intended for reporting
errors and in the range 16384-65535 for other status
information. An implementation that receives a NOTIFY
packet with a NOTIFICATION error parameter in response to a
request packet (e.g., I1, I2, UPDATE) SHOULD assume that
the corresponding request has failed entirely.
Unrecognized error types MUST be ignored except that they
SHOULD be logged.
</t>
<t>
Notify payloads with status types MUST be ignored if not
recognized.
</t>
<!--TH: We have to add notifies for unsupported DH and HIT Suites -->
<figure>
<artwork>
NOTIFICATION PARAMETER - ERROR TYPES Value
------------------------------------ -----
UNSUPPORTED_CRITICAL_PARAMETER_TYPE 1
Sent if the parameter type has the "critical" bit set and the
parameter type is not recognized. Notification Data contains
the two-octet parameter type.
INVALID_SYNTAX 7
Indicates that the HIP message received was invalid because
some type, length, or value was out of range or because the
request was rejected for policy reasons. To avoid a denial-
of-service attack using forged messages, this status may only be
returned for packets whose HIP_MAC (if present) and SIGNATURE have
been verified. This status MUST be sent in response to any
error not covered by one of the other status types, and should
not contain details to avoid leaking information to someone
probing a node. To aid debugging, more detailed error
information SHOULD be written to a console or log.
NO_DH_PROPOSAL_CHOSEN 14
None of the proposed group IDs was acceptable.
INVALID_DH_CHOSEN 15
The DH Group ID field does not correspond to one offered
by the Responder.
NO_HIP_PROPOSAL_CHOSEN 16
None of the proposed HIT Suites or HIP Encryption Algorithms was
acceptable.
INVALID_HIP_CIPHER_CHOSEN 17
The HIP_CIPHER Crypto ID does not correspond to
one offered by the Responder.
AUTHENTICATION_FAILED 24
Sent in response to a HIP signature failure, except when
the signature verification fails in a NOTIFY message.
CHECKSUM_FAILED 26
Sent in response to a HIP checksum failure.
HIP_MAC_FAILED 28
Sent in response to a HIP HMAC failure.
ENCRYPTION_FAILED 32
The Responder could not successfully decrypt the
ENCRYPTED parameter.
INVALID_HIT 40
Sent in response to a failure to validate the peer's
HIT from the corresponding HI.
BLOCKED_BY_POLICY 42
The Responder is unwilling to set up an association
for some policy reason (e.g., received HIT is NULL
and policy does not allow opportunistic mode).
SERVER_BUSY_PLEASE_RETRY 44
The Responder is unwilling to set up an association as it is
suffering under some kind of overload and has chosen to shed load
by rejecting the Initiator's request. The Initiator may retry;
however, the Initiator MUST find another (different) puzzle
solution for any such retries. Note that the Initiator may need
to obtain a new puzzle with a new I1/R1 exchange.
NOTIFY MESSAGES - STATUS TYPES Value
------------------------------ -----
I2_ACKNOWLEDGEMENT 16384
The Responder has an I2 from the Initiator but had to queue the
I2 for processing. The puzzle was correctly solved and the
Responder is willing to set up an association but currently has a
number of I2s in the processing queue. R2 will be sent after the
I2 has been processed.
</artwork>
</figure>
</section>
<section anchor="sec-echo-request-signed" title="ECHO_REQUEST_SIGNED">
<figure>
<artwork>
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opaque data (variable length) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type 897
Length variable
Opaque data opaque data, supposed to be meaningful only to the
node that sends ECHO_REQUEST_SIGNED and receives a
corresponding ECHO_RESPONSE_SIGNED or
ECHO_RESPONSE_UNSIGNED.
</artwork>
</figure>
<t>
The ECHO_REQUEST_SIGNED parameter contains an opaque blob
of data that the sender wants to get echoed back in the
corresponding reply packet.
</t>
<t>
The ECHO_REQUEST_SIGNED and corresponding echo response
parameters MAY be used for any purpose where a node wants
to carry some state in a request packet and get it back in
a response packet. The ECHO_REQUEST_SIGNED is covered by
the HIP_MAC and SIGNATURE. A HIP packet can contain only
one ECHO_REQUEST_SIGNED or ECHO_REQUEST_UNSIGNED parameter.
The ECHO_REQUEST_SIGNED parameter MUST be responded to with
a corresponding echo response. ECHO_RESPONSE_SIGNED SHOULD
be used, but if it is not possible, e.g., due to a
middlebox-provided response, it MAY be responded to with an
ECHO_RESPONSE_UNSIGNED.
</t>
</section>
<section anchor="sec-echo-request-unsigned"
title="ECHO_REQUEST_UNSIGNED">
<figure>
<artwork>
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opaque data (variable length) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type 63661
Length variable
Opaque data opaque data, supposed to be meaningful only to the
node that sends ECHO_REQUEST_UNSIGNED and receives a
corresponding ECHO_RESPONSE_UNSIGNED.
</artwork>
</figure>
<t>
The ECHO_REQUEST_UNSIGNED parameter contains an opaque blob
of data that the sender wants to get echoed back in the
corresponding reply packet.
</t>
<t>
The ECHO_REQUEST_UNSIGNED and corresponding echo response
parameters MAY be used for any purpose where a node wants
to carry some state in a request packet and get it back in
a response packet. The ECHO_REQUEST_UNSIGNED is not
covered by the HIP_MAC and SIGNATURE. A HIP packet can
contain one or more ECHO_REQUEST_UNSIGNED parameters. It
is possible that middleboxes add ECHO_REQUEST_UNSIGNED
parameters in HIP packets passing by. The sender has to
create the Opaque field so that it can later identify and
remove the corresponding ECHO_RESPONSE_UNSIGNED parameter.
</t>
<t>
The ECHO_REQUEST_UNSIGNED parameter MUST be responded to
with an ECHO_RESPONSE_UNSIGNED parameter.
</t>
</section>
<section anchor="echo_response_signed"
title="ECHO_RESPONSE_SIGNED">
<figure>
<artwork>
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opaque data (variable length) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type 961
Length variable
Opaque data opaque data, copied unmodified from the
ECHO_REQUEST_SIGNED or ECHO_REQUEST_UNSIGNED
parameter that triggered this response.
</artwork>
</figure>
<t>
The ECHO_RESPONSE_SIGNED parameter contains an opaque blob
of data that the sender of the ECHO_REQUEST_SIGNED wants to
get echoed back. The opaque data is copied unmodified from
the ECHO_REQUEST_SIGNED parameter.
</t>
<t>
The ECHO_REQUEST_SIGNED and ECHO_RESPONSE_SIGNED parameters
MAY be used for any purpose where a node wants to carry
some state in a request packet and get it back in a
response packet. The ECHO_RESPONSE_SIGNED is covered by
the HIP_MAC and SIGNATURE.
</t>
</section>
<section anchor="echo_response_unsigned"
title="ECHO_RESPONSE_UNSIGNED">
<figure>
<artwork>
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opaque data (variable length) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type 63425
Length variable
Opaque data opaque data, copied unmodified from the
ECHO_REQUEST_SIGNED or ECHO_REQUEST_UNSIGNED
parameter that triggered this response.
</artwork>
</figure>
<t>
The ECHO_RESPONSE_UNSIGNED parameter contains an opaque
blob of data that the sender of the ECHO_REQUEST_SIGNED or
ECHO_REQUEST_UNSIGNED wants to get echoed back. The opaque
data is copied unmodified from the corresponding echo
request parameter.
</t>
<t>
The echo request and ECHO_RESPONSE_UNSIGNED parameters MAY
be used for any purpose where a node wants to carry some
state in a request packet and get it back in a response
packet. The ECHO_RESPONSE_UNSIGNED is not covered by the
HIP_MAC and SIGNATURE.
</t>
</section>
</section>
<section title="HIP Packets">
<t>
There are eight basic HIP packets (see <xref
target="table_hip_packets" />). Four are for the HIP base
exchange, one is for updating, one is for sending
notifications, and two are for closing a HIP association.
</t>
<?rfc compact="no"?>
<texttable title="HIP packets and packet type numbers"
anchor="table_hip_packets">
<ttcol width="25%" align="center">Packet type</ttcol>
<ttcol align="left">Packet name</ttcol>
<c>1</c><c>I1 - the HIP Initiator Packet</c>
<c>2</c><c>R1 - the HIP Responder Packet</c>
<c>3</c><c>I2 - the Second HIP Initiator Packet</c>
<c>4</c><c>R2 - the Second HIP Responder Packet</c>
<c>16</c><c>UPDATE - the HIP Update Packet</c>
<c>17</c><c>NOTIFY - the HIP Notify Packet</c>
<c>18</c><c>CLOSE - the HIP Association Closing Packet</c>
<c>19</c><c>CLOSE_ACK - the HIP Closing Acknowledgment Packet</c>
</texttable>
<?rfc compact="yes"?>
<t>Packets consist of the fixed header as described in <xref
target="ssec-payload" />, followed by the parameters. The
parameter part, in turn, consists of zero or more TLV-coded
parameters.</t>
<t>
In addition to the base packets, other packet types will be
defined later in separate specifications. For example,
support for mobility and multi-homing is not included in this
specification.
</t>
<t>
See <xref target="notation">Notation</xref> for used operations.
</t>
<t>
In the future, an OPTIONAL upper-layer payload MAY follow the
HIP header. The Next Header field in the header indicates if
there is additional data following the HIP header. The HIP
packet, however, MUST NOT be fragmented. This limits the
size of the possible additional data in the packet.
</t>
<section anchor="I1" title="I1 - the HIP Initiator Packet">
<t>The HIP header values for the I1 packet:</t>
<figure>
<artwork>
Header:
Packet Type = 1
SRC HIT = Initiator's HIT
DST HIT = Responder's HIT, or NULL
IP ( HIP ( DH_GROUP_LIST ) )
</artwork>
</figure>
<t>The I1 packet contains the fixed HIP header and the
Initiator's DH_GROUP_LIST.</t>
<t>Valid control bits: none</t>
<t>
The Initiator gets the Responder's HIT either from a DNS
lookup of the Responder's FQDN, from some other repository,
or from a local table. If the Initiator does not know the
Responder's HIT, it may attempt to use opportunistic mode
by using NULL (all zeros) as the Responder's HIT. See also
<xref target="op_mode">"HIP Opportunistic Mode"</xref>.
</t>
<t>
Since this packet is so easy to spoof even if it were
signed, no attempt is made to add to its generation or
processing cost.
</t>
<t>
The Initiator includes a DH_GROUP_LIST parameter in the I1
to inform the Responder of its preferred DH Group IDs.
Note that the DH_GROUP_LIST in the I1 packet is not
protected by a signature.
</t>
<t>
Implementations MUST be able to handle a storm of received
I1 packets, discarding those with common content that
arrive within a small time delta.
</t>
</section>
<section anchor="R1" title="R1 - the HIP Responder Packet">
<t>The HIP header values for the R1 packet:</t>
<figure>
<artwork>
Header:
Packet Type = 2
SRC HIT = Responder's HIT
DST HIT = Initiator's HIT
IP ( HIP ( [ R1_COUNTER, ]
PUZZLE,
DIFFIE_HELLMAN,
HIP_CIPHER,
HOST_ID,
HIT_SUITE_LIST,
DH_GROUP_LIST,
[ ECHO_REQUEST_SIGNED, ]
HIP_SIGNATURE_2 )
<, ECHO_REQUEST_UNSIGNED >i)
</artwork>
</figure>
<t>
Valid control bits: A
</t>
<t>
If the Responder's HI is an anonymous one, the A control
MUST be set.
</t>
<t>
The Initiator's HIT MUST match the one received in I1. If
the Responder has multiple HIs, the Responder's HIT used
MUST match Initiator's request. If the Initiator used
opportunistic mode, the Responder may select freely among
its HIs. See also <xref target="op_mode">"HIP
Opportunistic Mode"</xref>.
</t>
<t>
The R1 generation counter is used to determine the
currently valid generation of puzzles. The value is
increased periodically, and it is RECOMMENDED that it is
increased at least as often as solutions to old puzzles are
no longer accepted.
</t>
<t>
The Puzzle contains a Random #I and the difficulty K.
The difficulty K indicates the number of lower-order
bits, in the puzzle hash result, that must be zeros; see
<xref target="puzzle_exchange"/>. The Random #I is not
covered by the signature and must be zeroed during the
signature calculation, allowing the sender to select and
set the #I into a precomputed R1 just prior sending it to
the peer.
</t>
<t>
The Responder selects the Diffie-Hellman public value based
on the Initiator's preference expressed in the
DH_GROUP_LIST parameter in the I1. The Responder sends back
its own preference based on which it chose the DH public
value as DH_GROUP_LIST. This allows the Initiator to
determine whether its own DH_GROUP_LIST in the I1 was
manipulated by an attacker.
</t>
<t>
The Diffie-Hellman public value is ephemeral, and one value
SHOULD be used only for one connection. Once the Responder
has received a valid response to an R1 packet, that
Diffie-Hellman value SHOULD be deprecated. Because it is
possible that the Responder has sent the same
Diffie-Hellman value to different hosts simultaneously in
corresponding R1 packets, those responses should also be
accepted. However, as a defense against I1 storms, an
implementation MAY propose, and re-use if not avoidable,
the same Diffie-Hellman value for a period of time, for
example, 15 minutes. By using a small number of different
puzzles for a given Diffie-Hellman value, the R1 packets
can be precomputed and delivered as quickly as I1 packets
arrive. A scavenger process should clean up unused
Diffie-Hellman values and puzzles.
</t>
<t>
Re-using Diffie-Hellman public keys opens up the potential
security risk of more than one Initiator ending up with the
same keying material (due to faulty random number
generators). Also, more than one Initiator using the same
Responder public key half may lead to potentially easier
cryptographic attacks and to imperfect forward security.
</t>
<t>
However, these risks involved in re-using the same key are
statistical; that is, the authors are not aware of any
mechanism that would allow manipulation of the protocol so
that the risk of the re-use of any given Responder
Diffie-Hellman public key would differ from the base
probability. Consequently, it is RECOMMENDED that
implementations avoid re-using the same DH key with
multiple Initiators, but because the risk is considered
statistical and not known to be manipulable, the
implementations MAY re-use a key in order to ease
resource-constrained implementations and to increase the
probability of successful communication with legitimate
clients even under an I1 storm. In particular, when it is
too expensive to generate enough precomputed R1 packets to
supply each potential Initiator with a different DH key,
the Responder MAY send the same DH key to several
Initiators, thereby creating the possibility of multiple
legitimate Initiators ending up using the same
Responder-side public key. However, as soon as the
Responder knows that it will use a particular DH key, it
SHOULD stop offering it. This design is aimed to allow
resource-constrained Responders to offer services under I1
storms and to simultaneously make the probability of DH
key re-use both statistical and as low as possible.
</t>
<t>
If a future version of this protocol is considered, we
strongly recommend that these issues be studied again.
Especially, the current design allows hosts to become
potentially more vulnerable to a statistical,
low-probability problem during I1 storm attacks than what
they are if no attack is taking place; whether this is
acceptable or not should be reconsidered in the light of
any new experience gained.
</t>
<t>
The HIP_CIPHER contains the encryption algorithms
supported by the Responder to encrypt the ENCRYPTED
parameter, in the order of preference. All implementations MUST support
AES <xref target="RFC3602" />.
</t>
<t>
The HIT_SUITE_LIST parameter is an ordered list of the
Responder's preferred and supported HIT Suites. The list
allows the Initiator to determine whether its own source
HIT is suitable.
</t>
<t>
The ECHO_REQUEST_SIGNED and ECHO_REQUEST_UNSIGNED contains
data that the sender wants to receive unmodified in the
corresponding response packet in the ECHO_RESPONSE_SIGNED
or ECHO_RESPONSE_UNSIGNED parameter.
</t>
<t>
The signature is calculated over the whole HIP envelope,
after setting the Initiator's HIT, header checksum, as well
as the Opaque field and the Random #I in the PUZZLE
parameter temporarily to zero, and excluding any parameters
that follow the signature, as described in <xref
target="HIP_SIGNATURE_2" />. This allows the Responder to
use precomputed R1s. The Initiator SHOULD validate this
signature. It SHOULD check that the Responder's HI
received matches with the one expected, if any.
</t>
</section>
<section anchor="I2" title="I2 - the Second HIP Initiator Packet">
<t>The HIP header values for the I2 packet:</t>
<figure>
<artwork>
Header:
Type = 3
SRC HIT = Initiator's HIT
DST HIT = Responder's HIT
IP ( HIP ( [R1_COUNTER,]
SOLUTION,
DIFFIE_HELLMAN,
HIP_CIPHER,
ENCRYPTED { HOST_ID } or HOST_ID,
[ ECHO_RESPONSE_SIGNED ,]
HIP_MAC,
HIP_SIGNATURE
<, ECHO_RESPONSE_UNSIGNED>i ) )
</artwork>
</figure>
<t>
Valid control bits: A
</t>
<t>
The HITs used MUST match the ones used previously.
</t>
<t>
If the Initiator's HI is an anonymous one, the A control
MUST be set.
</t>
<t>
The Initiator MAY include an unmodified copy of the
R1_COUNTER parameter received in the corresponding R1
packet into the I2 packet.
</t>
<t>
The Solution contains the Random #I from R1 and the
computed #J. The low-order K bits of the RHASH(I | ... |
J) MUST be zero.
</t>
<t>
The Diffie-Hellman value is ephemeral. If precomputed, a
scavenger process should clean up unused Diffie-Hellman
values. The Responder may re-use Diffie-Hellman values
under some conditions as specified in <xref target="R1" />.
</t>
<t>
The HIP_CIPHER contains the single encryption
transform selected by the Initiator, that will be used to
encrypt the ENCRYPTED parameter. The chosen cipher MUST
correspond to one offered by the Responder in the R1. All
implementations MUST support AES m <xref target="RFC3602"
/>.
</t>
<t>
The Initiator's HI MAY be encrypted using the
HIP_CIPHER encryption algorithm. The keying material
is derived from the Diffie-Hellman exchanged as defined in
<xref target="keymat" />.
</t>
<t>
The ECHO_RESPONSE_SIGNED and ECHO_RESPONSE_UNSIGNED contain
the unmodified Opaque data copied from the corresponding
echo request parameter.
</t>
<t>
The HMAC is calculated over the whole HIP envelope,
excluding any parameters after the HIP_MAC, as described in
<xref target="hmac-processing" />. The Responder MUST
validate the HIP_MAC.
</t>
<t>
The signature is calculated over the whole HIP envelope,
excluding any parameters after the HIP_SIGNATURE, as
described in <xref target="hip-signature" />. The
Responder MUST validate this signature. It MAY use either
the HI in the packet or the HI acquired by some other
means.
</t>
</section>
<section anchor="R2" title="R2 - the Second HIP Responder Packet">
<t>The HIP header values for the R2 packet:</t>
<figure>
<artwork>
Header:
Packet Type = 4
SRC HIT = Responder's HIT
DST HIT = Initiator's HIT
IP ( HIP ( HIP_MAC_2, HIP_SIGNATURE ) )
</artwork>
</figure>
<t>Valid control bits: none</t>
<t>
The HIP_MAC_2 is calculated over the whole HIP envelope,
with Responder's HOST_ID parameter concatenated with the
HIP envelope. The HOST_ID parameter is removed after the
HMAC calculation. The procedure is described in <xref
target="hmac-processing" />.
</t>
<t>
The signature is calculated over the whole HIP envelope.
</t>
<t>
The Initiator MUST validate both the HIP_MAC and the signature.
</t>
</section>
<section anchor="UPDATE" title="UPDATE - the HIP Update Packet">
<t>Support for the UPDATE packet is MANDATORY.</t>
<t>The HIP header values for the UPDATE packet:</t>
<figure>
<artwork>
Header:
Packet Type = 16
SRC HIT = Sender's HIT
DST HIT = Recipient's HIT
IP ( HIP ( [SEQ, ACK, ] HIP_MAC, HIP_SIGNATURE ) )
</artwork>
</figure>
<t>Valid control bits: None</t>
<t>
The UPDATE packet contains mandatory HIP_MAC and
HIP_SIGNATURE parameters, and other optional parameters.
</t>
<t>
The UPDATE packet contains zero or one SEQ parameter. The
presence of a SEQ parameter indicates that the receiver
MUST ACK the UPDATE. An UPDATE that does not contain a SEQ
parameter is simply an ACK of a previous UPDATE and itself
MUST NOT be ACKed.
</t>
<t>
An UPDATE packet contains zero or one ACK parameters. The
ACK parameter echoes the SEQ sequence number of the UPDATE
packet being ACKed. A host MAY choose to ACK more than one
UPDATE packet at a time; e.g., the ACK may contain the last
two SEQ values received, for robustness to ACK loss. ACK
values are not cumulative; each received unique SEQ value
requires at least one corresponding ACK value in reply.
Received ACKs that are redundant are ignored.
</t>
<t>
The UPDATE packet may contain both a SEQ and an ACK
parameter. In this case, the ACK is being piggybacked on
an outgoing UPDATE. In general, UPDATEs carrying SEQ
SHOULD be ACKed upon completion of the processing of the
UPDATE. A host MAY choose to hold the UPDATE carrying ACK
for a short period of time to allow for the possibility of
piggybacking the ACK parameter, in a manner similar to TCP
delayed acknowledgments.
</t>
<t>
A sender MAY choose to forgo reliable transmission of a
particular UPDATE (e.g., it becomes overcome by events).
The semantics are such that the receiver MUST acknowledge
the UPDATE, but the sender MAY choose to not care about
receiving the ACK.
</t>
<t>
UPDATEs MAY be retransmitted without incrementing SEQ. If
the same subset of parameters is included in multiple
UPDATEs with different SEQs, the host MUST ensure that the
receiver's processing of the parameters multiple times will
not result in a protocol error.
</t>
</section>
<section title="NOTIFY - the HIP Notify Packet">
<t>
The NOTIFY packet is OPTIONAL. The NOTIFY packet MAY be
used to provide information to a peer. Typically, NOTIFY
is used to indicate some type of protocol error or
negotiation failure. NOTIFY packets are unacknowledged.
The receiver can handle the packet only as informational,
and SHOULD NOT change its HIP state (<xref target="states"
/>) based purely on a received NOTIFY packet.
</t>
<t>The HIP header values for the NOTIFY packet:</t>
<figure>
<artwork>
Header:
Packet Type = 17
SRC HIT = Sender's HIT
DST HIT = Recipient's HIT, or zero if unknown
IP ( HIP (<NOTIFICATION>i, [HOST_ID, ] HIP_SIGNATURE) )
</artwork>
</figure>
<t>Valid control bits: None</t>
<t>
The NOTIFY packet is used to carry one or more NOTIFICATION
parameters.
</t>
</section>
<section anchor="CLOSE"
title="CLOSE - the HIP Association Closing Packet">
<t>The HIP header values for the CLOSE packet:</t>
<figure>
<artwork>
Header:
Packet Type = 18
SRC HIT = Sender's HIT
DST HIT = Recipient's HIT
IP ( HIP ( ECHO_REQUEST_SIGNED, HIP_MAC, HIP_SIGNATURE ) )
</artwork>
</figure>
<t>Valid control bits: none</t>
<t>
The sender MUST include an ECHO_REQUEST_SIGNED used to
validate CLOSE_ACK received in response, and both an
HIP_MAC and a signature (calculated over the whole HIP
envelope).
</t>
<t>
The receiver peer MUST validate both the HIP_MAC and the
signature if it has a HIP association state, and MUST reply
with a CLOSE_ACK containing an ECHO_RESPONSE_SIGNED
corresponding to the received ECHO_REQUEST_SIGNED.
</t>
</section>
<section anchor="CLOSE_ACK"
title="CLOSE_ACK - the HIP Closing Acknowledgment Packet">
<t>
The HIP header values for the CLOSE_ACK packet:
</t>
<figure>
<artwork>
Header:
Packet Type = 19
SRC HIT = Sender's HIT
DST HIT = Recipient's HIT
IP ( HIP ( ECHO_RESPONSE_SIGNED, HIP_MAC, HIP_SIGNATURE ) )
</artwork>
</figure>
<t>Valid control bits: none</t>
<t>
The sender MUST include both an HMAC and signature
(calculated over the whole HIP envelope).
</t>
<t>
The receiver peer MUST validate both the HMAC and the
signature.
</t>
</section>
</section>
<section anchor="ICMP" title="ICMP Messages">
<t>
When a HIP implementation detects a problem with an incoming
packet, and it either cannot determine the identity of the
sender of the packet or does not have any existing HIP
association with the sender of the packet, it MAY respond
with an ICMP packet. Any such replies MUST be rate-limited
as described in <xref target="RFC2463" />. In most cases,
the ICMP packet will have the Parameter Problem type (12 for
ICMPv4, 4 for ICMPv6), with the Pointer field pointing to the
field that caused the ICMP message to be generated.
</t>
<section title="Invalid Version">
<t>
If a HIP implementation receives a HIP packet that has an
unrecognized HIP version number, it SHOULD respond,
rate-limited, with an ICMP packet with type Parameter
Problem, the Pointer pointing to the VER./RES. byte in the
HIP header.
</t>
</section>
<section
title="Other Problems with the HIP Header and Packet Structure">
<t>
If a HIP implementation receives a HIP packet that has
other unrecoverable problems in the header or packet
format, it MAY respond, rate-limited, with an ICMP packet
with type Parameter Problem, the Pointer pointing to the
field that failed to pass the format checks. However, an
implementation MUST NOT send an ICMP message if the
checksum fails; instead, it MUST silently drop the packet.
</t>
</section>
<section title="Invalid Puzzle Solution">
<t>
If a HIP implementation receives an I2 packet that has an
invalid puzzle solution, the behavior depends on the
underlying version of IP. If IPv6 is used, the
implementation SHOULD respond with an ICMP packet with type
Parameter Problem, the Pointer pointing to the beginning of
the Puzzle solution #J field in the SOLUTION payload in the
HIP message.
</t>
<t>
If IPv4 is used, the implementation MAY respond with an
ICMP packet with the type Parameter Problem, copying enough
of bytes from the I2 message so that the SOLUTION parameter
fits into the ICMP message, the Pointer pointing to the
beginning of the Puzzle solution #J field, as in the IPv6
case. Note, however, that the resulting ICMPv4 message
exceeds the typical ICMPv4 message size as defined in <xref
target="RFC0792" />.
</t>
</section>
<section anchor="non-existing-hip" title="Non-Existing HIP Association">
<t>
If a HIP implementation receives a CLOSE or UPDATE packet,
or any other packet whose handling requires an existing
association, that has either a Receiver or Sender HIT that
does not match with any existing HIP association, the
implementation MAY respond, rate-limited, with an ICMP
packet with the type Parameter Problem, and with the
Pointer pointing to the beginning of the first HIT that
does not match.
</t>
<t>
A host MUST NOT reply with such an ICMP if it receives any
of the following messages: I1, R2, I2, R2, and NOTIFY.
When introducing new packet types, a specification SHOULD
define the appropriate rules for sending or not sending
this kind of ICMP reply.
</t>
</section>
</section>
</section>
<section anchor="packet_processing" title="Packet Processing">
<t>
Each host is assumed to have a single HIP protocol
implementation that manages the host's HIP associations and
handles requests for new ones. Each HIP association is
governed by a conceptual state machine, with states defined
above in <xref target="state-machine" />. The HIP
implementation can simultaneously maintain HIP associations
with more than one host. Furthermore, the HIP implementation
may have more than one active HIP association with another
host; in this case, HIP associations are distinguished by their
respective HITs. It is not possible to have more than one HIP
association between any given pair of HITs. Consequently, the
only way for two hosts to have more than one parallel
association is to use different HITs, at least at one end.
</t>
<t>
The processing of packets depends on the state of the HIP
association(s) with respect to the authenticated or apparent
originator of the packet. A HIP implementation determines
whether it has an active association with the originator of the
packet based on the HITs. In the case of user data carried in
a specific transport format, the transport format document
specifies how the incoming packets are matched with the active
associations.
</t>
<section title="Processing Outgoing Application Data">
<t>
In a HIP host, an application can send application-level data
using an identifier specified via the underlying API. The
API can be a backwards-compatible API (see <xref
target="RFC5338" />), using identifiers that look similar to
IP addresses, or a completely new API, providing enhanced
services related to Host Identities. Depending on the HIP
implementation, the identifier provided to the application
may be different; for example, it can be a HIT or an IP
address.
</t>
<t>
The exact format and method for transferring the data from the
source HIP host to the destination HIP host is defined in the
corresponding transport format document. The actual data is
transferred in the network using the appropriate source and
destination IP addresses.
</t>
<t>
In this document, conceptual processing rules are defined
only for the base case where both hosts have only single
usable IP addresses; the multi-address multi-homing case will
be specified separately.
</t>
<t>
The following conceptual algorithm describes the steps that
are required for handling outgoing datagrams destined to a
HIT.
<list style="numbers">
<t>
If the datagram has a specified source address, it MUST
be a HIT. If it is not, the implementation MAY replace
the source address with a HIT. Otherwise, it MUST drop
the packet.
</t>
<t>
If the datagram has an unspecified source address, the
implementation must choose a suitable source HIT for the
datagram.
</t>
<t>
If there is no active HIP association with the given
<source, destination> HIT pair, one must be created
by running the base exchange. While waiting for the base
exchange to complete, the implementation SHOULD queue at
least one packet per HIP association to be formed, and it
MAY queue more than one.
</t>
<t>
Once there is an active HIP association for the given
<source, destination> HIT pair, the outgoing
datagram is passed to transport handling. The possible
transport formats are defined in separate documents, of
which the ESP transport format for HIP is mandatory for
all HIP implementations.
</t>
<t>
Before sending the packet, the HITs in the datagram are
replaced with suitable IP addresses. For IPv6, the rules
defined in <xref target="RFC3484" /> SHOULD be followed.
Note that this HIT-to-IP-address conversion step MAY also
be performed at some other point in the stack, e.g.,
before wrapping the packet into the output format.
</t>
</list>
</t>
</section>
<section title="Processing Incoming Application Data">
<t>
The following conceptual algorithm describes the incoming
datagram handling when HITs are used at the receiving host as
application-level identifiers. More detailed steps for
processing packets are defined in corresponding transport
format documents.
</t>
<t>
<list style="numbers">
<t>
The incoming datagram is mapped to an existing HIP
association, typically using some information from the
packet. For example, such mapping may be based on the ESP
Security Parameter Index (SPI).
</t>
<t>
The specific transport format is unwrapped, in a way
depending on the transport format, yielding a packet that
looks like a standard (unencrypted) IP packet. If
possible, this step SHOULD also verify that the packet
was indeed (once) sent by the remote HIP host, as
identified by the HIP association.
<vspace blankLines='1' />
Depending on the used transport mode, the verification
method can vary. While the HI (as well as HIT) is used as
the higher-layer identifier, the verification method has
to verify that the data packet was sent by a node
identity and that the actual identity maps to this
particular HIT. When using ESP transport format <xref
target="RFC5202" />, the verification is done using the
SPI value in the data packet to find the corresponding SA
with associated HIT and key, and decrypting the packet
with that associated key.
</t>
<t>
The IP addresses in the datagram are replaced with the
HITs associated with the HIP association. Note that this
IP-address-to-HIT conversion step MAY also be performed
at some other point in the stack.
</t>
<t>
The datagram is delivered to the upper layer. When
demultiplexing the datagram, the right upper-layer socket
is based on the HITs.
</t>
</list>
</t>
</section>
<section title="Solving the Puzzle">
<t>
This subsection describes the puzzle-solving details.
</t>
<t>
In R1, the values I and K are sent in network byte order.
Similarly, in I2, the values I and J are sent in network byte
order. The hash is created by concatenating, in network byte
order, the following data, in the following order and using
the RHASH algorithm:
<list>
<t>
n-bit random value I (where n is RHASH-len/2), in network
byte order, as appearing in R1 and I2.
</t>
<t>
128-bit Initiator's HIT, in network byte order, as
appearing in the HIP Payload in R1 and I2.
</t>
<t>
128-bit Responder's HIT, in network byte order, as
appearing in the HIP Payload in R1 and I2.
</t>
<t>
n-bit random value J (where n is RHASH-len/2), in
network byte order, as appearing in I2.
</t>
</list>
In order to be a valid response puzzle, the K low-order bits
of the resulting RHASH digest must be zero.
</t>
<t>
Notes:
<list>
<t>
i) The length of the data to be hashed is variable
depending on the output length of the Responder's hash
function RHASH.
</t>
<t>
ii) All the data in the hash input MUST be in network
byte order.
</t>
<t>
iii) The order of the Initiator's and Responder's HITs
are different in the R1 and I2 packets; see <xref
target="ssec-payload" />. Care must be taken to copy the
values in the right order to the hash input.
</t>
</list>
</t>
<t>
The following procedure describes the processing steps
involved, assuming that the Responder chooses to
precompute the R1 packets:
</t>
<t>
<list style="hanging">
<t hangText="Precomputation by the Responder:">
<vspace blankLines="0" />
Sets up the puzzle difficulty K.
<vspace blankLines="0" />
Creates a signed R1 and caches it.
<vspace blankLines="0" />
</t>
<t hangText="Responder:">
<vspace blankLines="0" />
Selects a suitable cached R1.
<vspace blankLines="0" />
Generates a random number I.
<vspace blankLines="0" />
Sends I and K in an R1.
<vspace blankLines="0" />
Saves I and K for a Delta time.
<vspace blankLines="0" />
</t>
<t hangText="Initiator:">
<vspace blankLines="0" />
Generates repeated attempts to solve the puzzle
until a matching J is found:
<vspace blankLines="0" />
Ltrunc( RHASH( I | HIT-I | HIT-R | J ), K ) == 0
<vspace blankLines="0" />
Sends I and J in an I2.
<vspace blankLines="1" />
</t>
<t hangText="Responder:">
<vspace blankLines="0" />
Verifies that the received I is a saved one.
<vspace blankLines="0" />
Finds the right K based on I.
<vspace blankLines="0" />
Computes V := Ltrunc( RHASH( I | HIT-I | HIT-R | J ), K )
<vspace blankLines="0" />
Rejects if V != 0
<vspace blankLines="0" />
Accept if V == 0
<vspace blankLines="0" />
</t>
</list>
</t>
</section>
<section title="HIP_MAC and SIGNATURE Calculation and Verification">
<t>
The following subsections define the actions for processing
HIP_MAC, HIP_MAC_2, HIP_SIGNATURE and HIP_SIGNATURE_2
parameters.
</t>
<section anchor="hmac-processing" title="HMAC Calculation">
<t>
The following process applies both to the HIP_MAC and
HIP_MAC_2 parameters. When processing HIP_MAC_2, the
difference is that the HIP_MAC calculation includes a
pseudo HOST_ID field containing the Responder's information
as sent in the R1 packet earlier.
</t>
<t>
Both the Initiator and the Responder should take some care
when verifying or calculating the HIP_MAC_2. Specifically,
the Responder should preserve other parameters than the
HOST_ID when sending the R2. Also, the Initiator has to
preserve the HOST_ID exactly as it was received in the R1
packet.
</t>
<t>
The scope of the calculation for HIP_MAC and HIP_MAC_2 is:
</t>
<figure>
<artwork>
HMAC: { HIP header | [ Parameters ] }
</artwork>
</figure>
<t>
where Parameters include all HIP parameters of the
packet that is being calculated with Type values from 1
to (HIP_MAC's Type value - 1) and exclude parameters with
Type values greater or equal to HIP_MAC's Type value.
</t>
<t>
During HIP_MAC calculation, the following applies:
<list style="symbols">
<t>
In the HIP header, the Checksum field is set to zero.
</t>
<t>
In the HIP header, the Header Length field value is
calculated to the beginning of the HIP_MAC parameter.
</t>
</list>
</t>
<t>
Parameter order is described in <xref target="tlvformat"
/>.
</t>
<figure>
<artwork>
HIP_MAC_2: { HIP header | [ Parameters ] | HOST_ID }
</artwork>
</figure>
<t>
where Parameters include all HIP parameters for the packet
that is being calculated with Type values from 1 to
(HIP_MAC_2's Type value - 1) and exclude parameters with
Type values greater or equal to HIP_MAC_2's Type value.
</t>
<t>
During HIP_MAC_2 calculation, the following applies:
<list style="symbols">
<t>
In the HIP header, the Checksum field is set to zero.
</t>
<t>
In the HIP header, the Header Length field value is
calculated to the beginning of the HIP_MAC_2 parameter
and added to the length of the concatenated HOST_ID
parameter length.
</t>
<t>
HOST_ID parameter is exactly in the form it was received
in the R1 packet from the Responder.
</t>
</list>
</t>
<t>
Parameter order is described in <xref target="tlvformat"
/>, except that the HOST_ID parameter in this calculation is
added to the end.
</t>
<t>
The HIP_MAC parameter is defined in <xref target="HIP_MAC"
/> and the HIP_MAC_2 parameter in <xref target="HIP_MAC_2"
/>. The HMAC calculation and verification process (the
process applies both to HIP_MAC and HIP_MAC_2 except where
HIP_MAC_2 is mentioned separately) is as follows:
</t>
<t>Packet sender:
<list style="numbers">
<t>
Create the HIP packet, without the HIP_MAC, HIP_SIGNATURE,
HIP_SIGNATURE_2, or any other parameter with greater Type
value than the HIP_MAC parameter has.
</t>
<t>In case of HIP_MAC_2 calculation, add a HOST_ID (Responder)
parameter to the end of the packet.
</t>
<t>
Calculate the Header Length field in the HIP header
including the added HOST_ID parameter in case of HIP_MAC_2.
</t>
<t>
Compute the HMAC using either HIP-gl or HIP-lg integrity
key retrieved from KEYMAT as defined in <xref
target="keymat" />.
</t>
<t>
In case of HIP_MAC_2, remove the HOST_ID parameter from the
packet.
</t>
<t>
Add the HIP_MAC parameter to the packet and any
parameter with greater Type value than the HIP_MAC's
(HIP_MAC_2's) that may follow, including possible
HIP_SIGNATURE or HIP_SIGNATURE_2 parameters
</t>
<t>
Recalculate the Length field in the HIP header.
</t>
</list>
</t>
<t>Packet receiver:
<list style="numbers">
<t>Verify the HIP header Length field.</t>
<t>
Remove the HIP_MAC or HIP_MAC_2 parameter, as well as
all other parameters that follow it with greater Type
value including possible HIP_SIGNATURE or
HIP_SIGNATURE_2 fields, saving the contents if they
will be needed later.
</t>
<t>
In case of HIP_MAC_2, build and add a HOST_ID parameter
(with Responder information) to the packet. The HOST_ID
parameter should be identical to the one previously
received from the Responder.
</t>
<t>
Recalculate the HIP packet length in the HIP header and
clear the Checksum field (set it to all zeros). In
case of HIP_MAC_2, the length is calculated with the
added HOST_ID parameter.
</t>
<t>
Compute the HMAC using either HIP-gl or HIP-lg
integrity key as defined in <xref target="keymat" />
and verify it against the received HMAC.
</t>
<t>
Set Checksum and Header Length field in the HIP header
to original values.
</t>
<t>
In case of HIP_MAC_2, remove the HOST_ID parameter from
the packet before further processing.
</t>
</list>
</t>
</section>
<section anchor="sig-processing" title="Signature Calculation">
<t>
The following process applies both to the HIP_SIGNATURE and
HIP_SIGNATURE_2 parameters. When processing
HIP_SIGNATURE_2, the only difference is that instead of
HIP_SIGNATURE parameter, the HIP_SIGNATURE_2 parameter is
used, and the Initiator's HIT and PUZZLE Opaque and Random
#I fields are cleared (set to all zeros) before computing
the signature. The HIP_SIGNATURE parameter is defined in
<xref target="hip-signature" /> and the HIP_SIGNATURE_2
parameter in <xref target="HIP_SIGNATURE_2" />.
</t>
<t>
The scope of the calculation for HIP_SIGNATURE and
HIP_SIGNATURE_2 is:
</t>
<figure>
<artwork>
HIP_SIGNATURE: { HIP header | [ Parameters ] }
</artwork>
</figure>
<t>
where Parameters include all HIP parameters for the packet
that is being calculated with Type values from 1 to
(HIP_SIGNATURE's Type value - 1).
</t>
<t>
During signature calculation, the following apply:
<list style="symbols">
<t>
In the HIP header, the Checksum field is set to zero.
</t>
<t>
In the HIP header, the Header Length field value is
calculated to the beginning of the HIP_SIGNATURE
parameter.
</t>
</list>
</t>
<t>
Parameter order is described in <xref target="tlvformat" />.
</t>
<figure>
<artwork>
HIP_SIGNATURE_2: { HIP header | [ Parameters ] }
</artwork>
</figure>
<t>
where Parameters include all HIP parameters for the packet
that is being calculated with Type values from 1 to
(HIP_SIGNATURE_2's Type value - 1).
</t>
<t>
During signature calculation, the following apply:
<list style="symbols">
<t>
In the HIP header, the Initiator's HIT field and
Checksum fields are set to zero.
</t>
<t>
In the HIP header, the Header Length field value is
calculated to the beginning of the HIP_SIGNATURE_2
parameter.
</t>
<t>
PUZZLE parameter's Opaque and Random #I fields are set
to zero.
</t>
</list>
</t>
<t>
Parameter order is described in <xref target="tlvformat" />.
</t>
<t>
Signature calculation and verification process (the process
applies both to HIP_SIGNATURE and HIP_SIGNATURE_2 except
in the
case where HIP_SIGNATURE_2 is separately mentioned):
</t>
<t>Packet sender:
<list style="numbers">
<t>
Create the HIP packet without the HIP_SIGNATURE
parameter or any parameters that follow the
HIP_SIGNATURE parameter.
</t>
<t>
Calculate the Length field and zero the Checksum field
in the HIP header. In case of HIP_SIGNATURE_2, set
Initiator's HIT field in the HIP header as well as
PUZZLE parameter's Opaque and Random #I fields to
zero.
</t>
<t>
Compute the signature using the private key
corresponding to the Host Identifier (public key).
</t>
<t>
Add the HIP_SIGNATURE parameter to the packet.
</t>
<t>
Add any parameters that follow the HIP_SIGNATURE
parameter.
</t>
<t>
Recalculate the Length field in the HIP header, and
calculate the Checksum field.
</t>
</list>
</t>
<t>Packet receiver:
<list style="numbers">
<t>Verify the HIP header Length field.</t>
<t>
Save the contents of the HIP_SIGNATURE parameter and
any parameters following the HIP_SIGNATURE parameter
and remove them from the packet.
</t>
<t>
Recalculate the HIP packet Length in the HIP header and
clear the Checksum field (set it to all zeros). In
case of HIP_SIGNATURE_2, set Initiator's HIT field in
HIP header as well as PUZZLE parameter's Opaque and
Random #I fields to zero.
</t>
<t>
Compute the signature and verify it against the
received signature using the packet sender's Host
Identifier (public key).
</t>
<t>
Restore the original packet by adding removed
parameters (in step 2) and resetting the values that
were set to zero (in step 3).
</t>
</list>
</t>
<t>
The verification can use either the HI received from a HIP
packet, the HI from a DNS query, if the FQDN has been
received in the HOST_ID packet, or one received by some
other means.
</t>
</section>
</section>
<section anchor="keymat" title="HIP KEYMAT Generation">
<t>
HIP keying material is derived from the Diffie-Hellman
session key, Kij, produced during the HIP base exchange
(<xref target="auth_dh" />). The Initiator has Kij during
the creation of the I2 packet, and the Responder has Kij once
it receives the I2 packet. This is why I2 can already
contain encrypted information.
</t>
<t>The KEYMAT is derived by feeding Kij into HKDF <xref target="RFC5869"/>
using the RHASH hash function.</t>
<figure>
<artwork>
where
info = sort(HIT-I | HIT-R)
salt = I | J
</artwork>
</figure>
<t>
Sort(HIT-I | HIT-R) is defined as the network byte order
concatenation of the two HITs, with the smaller HIT preceding
the larger HIT, resulting from the numeric comparison of the
two HITs interpreted as positive (unsigned) 128-bit integers
in network byte order.
</t>
<t>
I and J values are from the puzzle and its solution that were
exchanged in R1 and I2 messages when this HIP association was
set up. Both hosts have to store I and J values for the HIP
association for future use.
</t>
<t>
The initial keys are drawn sequentially in the order that is
determined by the numeric comparison of the two HITs, with
comparison method described in the previous paragraph.
HOST_g denotes the host with the greater HIT value, and
HOST_l the host with the lower HIT value.
</t>
<t>The drawing order for initial keys:
<list>
<t>HIP-gl encryption key for HOST_g's outgoing HIP packets</t>
<t>HIP-gl integrity (HMAC) key for HOST_g's outgoing HIP
packets</t>
<t>HIP-lg encryption key (currently unused) for HOST_l's
outgoing HIP packets</t>
<t>HIP-lg integrity (HMAC) key for HOST_l's outgoing HIP
packets</t>
</list>
</t>
<t>The number of bits drawn for a given algorithm is the
"natural" size of the keys. For the mandatory algorithms, the
following sizes apply:
<list style="hanging">
<t hangText="AES">128 or 256 bits</t>
<t hangText="SHA-1">160 bits</t>
<t hangText="SHA-256">256 bits</t>
<t hangText="SHA-384">384 bits</t>
<t hangText="NULL">0 bits</t>
</list>
</t>
<t>
If other key sizes are used, they must be treated as different
encryption algorithms and defined separately.
</t>
</section>
<section title="Initiation of a HIP Exchange">
<t>
An implementation may originate a HIP exchange to another
host based on a local policy decision, usually triggered by
an application datagram, in much the same way that an IPsec
IKE key exchange can dynamically create a Security
Association. Alternatively, a system may initiate a HIP
exchange if it has rebooted or timed out, or otherwise lost
its HIP state, as described in <xref target="reboot" />.
</t>
<t>
The implementation prepares an I1 packet and sends it to the
IP address that corresponds to the peer host. The IP address
of the peer host may be obtained via conventional mechanisms,
such as DNS lookup. The I1 contents are specified in <xref
target="I1" />. The selection of which Host Identity to use,
if a host has more than one to choose from, is typically a
policy decision.
</t>
<t>
The following steps define the conceptual processing rules for
initiating a HIP exchange:
<list style="numbers">
<t>
The Initiator gets one or more of the Responder's HITs and one or more
addresses either from a DNS lookup of the Responder's
FQDN, from some other repository, or from a local table.
If the Initiator does not know the Responder's HIT, it
may attempt opportunistic mode by using NULL (all zeros)
as the Responder's HIT. See also <xref target="op_mode">
"HIP Opportunistic Mode" </xref>. If the Initiator can
choose from multiple Responder HITs, it selects a HIT for
which the Initiator supports the HIT Suite.
</t>
<t>
The Initiator sends an I1 to one of the Responder's
addresses. The selection of which address to use is a
local policy decision.
</t>
<t>
The Initiator includes the DH_GROUP_LIST in the I1
packet. The selection and order of DH Group IDs in the
DH_GROUP_LIST MUST be stored by the Initiator because
this list is needed for later R1 processing. In most
cases, the preferences regarding the DH Groups will be
static, so no per-association storage is necessary.
</t>
<t>
Upon sending an I1, the sender transitions to state
I1-SENT, starts a timer whose timeout value SHOULD be
larger than the worst-case anticipated RTT, and SHOULD
increment a timeout counter associated with the I1.
</t>
<t>
Upon timeout, the sender SHOULD retransmit the I1 and
restart the timer, up to a maximum of I1_RETRIES_MAX
tries.
</t>
</list>
</t>
<section anchor="multi-i1" title="Sending Multiple I1s in Parallel">
<t>
For the sake of minimizing the session establishment
latency, an implementation MAY send the same I1 to more
than one of the Responder's addresses. However, it MUST
NOT send to more than three (3) addresses in parallel.
Furthermore, upon timeout, the implementation MUST refrain
from sending the same I1 packet to multiple addresses. That
is, if it retries to initialize the connection after
timeout, it MUST NOT send the I1 packet to more than one
destination address. These limitations are placed in order
to avoid congestion of the network, and potential DoS
attacks that might happen, e.g., because someone's claim to
have hundreds or thousands of addresses could generate a
huge number of I1 messages from the Initiator.
</t>
<t>
As the Responder is not guaranteed to distinguish the
duplicate I1s it receives at several of its addresses
(because it avoids storing states when it answers back an
R1), the Initiator may receive several duplicate R1s.
</t>
<t>
The Initiator SHOULD then select the initial preferred
destination address using the source address of the
selected received R1, and use the preferred address as a
source address for the I2. Processing rules for received
R1s are discussed in <xref target="inr1" />.
</t>
</section>
<section title="Processing Incoming ICMP Protocol Unreachable
Messages">
<t>
A host may receive an ICMP 'Destination Protocol
Unreachable' message as a response to sending a HIP I1
packet. Such a packet may be an indication that the peer
does not support HIP, or it may be an attempt to launch an
attack by making the Initiator believe that the Responder
does not support HIP.
</t>
<t>
When a system receives an ICMP 'Destination Protocol
Unreachable' message while it is waiting for an R1, it MUST
NOT terminate the wait. It MAY continue as if it had not
received the ICMP message, and send a few more I1s.
Alternatively, it MAY take the ICMP message as a hint that
the peer most probably does not support HIP, and return to
state UNASSOCIATED earlier than otherwise. However, at
minimum, it MUST continue waiting for an R1 for a
reasonable time before returning to UNASSOCIATED.
</t>
</section>
</section>
<section anchor="i1process" title="Processing Incoming I1 Packets">
<t>
An implementation SHOULD reply to an I1 with an R1 packet,
unless the implementation is unable or unwilling to set up a
HIP association. If the implementation is unable to set up a
HIP association, the host SHOULD send an ICMP Destination
Protocol Unreachable, Administratively Prohibited, message to
the I1 source address. If the implementation is unwilling to
set up a HIP association, the host MAY ignore the I1. This
latter case may occur during a DoS attack such as an I1
flood.
</t>
<t>
The implementation MUST be able to handle a storm of received
I1 packets, discarding those with common content that arrive
within a small time delta.
</t>
<t>
A spoofed I1 can result in an R1 attack on a system. An R1
sender MUST have a mechanism to rate-limit R1s to an address.
</t>
<t>
It is RECOMMENDED that the HIP state machine does not transition
upon sending an R1.
</t>
<t>
The following steps define the conceptual processing rules
for responding to an I1 packet:
<list style="numbers">
<t>
The Responder MUST check that the Responder's HIT in the
received I1 is either one of its own HITs or NULL.
</t>
<t>
If the Responder is in ESTABLISHED state, the Responder
MAY respond to this with an R1 packet, prepare to drop
existing SAs, and stay at ESTABLISHED state.
</t>
<t>
If the Responder is in I1-SENT state, it must make a
comparison between the sender's HIT and its own (i.e.,
the receiver's) HIT. If the sender's HIT is greater than
its own HIT, it should drop the I1 and stay at I1-SENT.
If the sender's HIT is smaller than its own HIT, it
should send R1 and stay at I1-SENT. The HIT comparison
goes similarly as in <xref target="keymat" />.
</t>
<t>
If the implementation chooses to respond to the I1 with
an R1 packet, it creates a new R1 or selects a
precomputed R1 according to the format described in <xref
target="R1" />. It creates or chooses an R1 that contains
its most preferred DH public value that is also contained
in the DH_GROUP_LIST in the I1 packet. If no suitable DH
Group ID was contained in the DH_GROUP_LIST in the I1
packet, it sends an R1 with an arbitrary DH public key.
</t>
<t>
The R1 MUST contain the received Responder's HIT, unless
the received HIT is NULL, in which case the Responder
SHOULD select a HIT that is constructed with the MUST
algorithm in <xref target="HI"/>, which is currently RSA.
Other than that, selecting the HIT is a local policy
matter.
</t>
<t>
The Responder sends the R1 to the source IP address of
the I1 packet.
</t>
</list>
</t>
<section title="R1 Management">
<t>
All compliant implementations MUST produce R1 packets. An
R1 packet MAY be precomputed. An R1 packet MAY be reused
for time Delta T, which is implementation dependent, and
SHOULD be deprecated and not used once a valid response I2
packet has been received from an Initiator. During an I1
message storm, an R1 packet may be re-used beyond this
limit. R1 information MUST NOT be discarded until Delta S
after T. Time S is the delay needed for the last I2
to arrive back to the Responder.
</t>
<t>
<!--TH: I added this short paragraph on different groups.
Depending on how we handle crypto agility and
pre-creation we will have to change it or we can
possibly skip it. If we want to optimize pre-creation
with signed hashes or hash trees we need to extend it.
However, I think we should try to keep it simple and
refrain from optimizing pre-creation.-->
Implementations that support multiple DH groups MAY
pre-compute R1 packets for each supported group so that
incoming I1 packets with different DH Group IDs in the
DH_GROUP_LIST can be served quickly.
</t>
<t>
An implementation MAY keep state about received I1s and
match the received I2s against the state, as discussed in
<xref target="hip-cookie" />.
</t>
</section>
<section title="Handling Malformed Messages">
<t>
If an implementation receives a malformed I1 message, it
SHOULD NOT respond with a NOTIFY message, as such practice
could open up a potential denial-of-service danger.
Instead, it MAY respond with an ICMP packet, as defined in
<xref target="ICMP" />.
</t>
</section>
</section>
<section anchor="inr1" title="Processing Incoming R1 Packets">
<t>
A system receiving an R1 MUST first check to see if it has
sent an I1 to the originator of the R1 (i.e., it is in state
I1-SENT). If so, it SHOULD process the R1 as described
below, send an I2, and go to state I2-SENT, setting a timer
to protect the I2. If the system is in state I2-SENT, it MAY
respond to an R1 if the R1 has a larger R1 generation
counter; if so, it should drop its state due to processing
the previous R1 and start over from state I1-SENT. If the
system is in any other state with respect to that host, it
SHOULD silently drop the R1.
</t>
<t>
When sending multiple I1s, an Initiator SHOULD wait for a
small amount of time after the first R1 reception to allow
possibly multiple R1s to arrive, and it SHOULD respond to an
R1 among the set with the largest R1 generation counter.
</t>
<t>
The following steps define the conceptual processing rules
for responding to an R1 packet:
<list style="numbers">
<t>
A system receiving an R1 MUST first check to see if it
has sent an I1 to the originator of the R1 (i.e., it has
a HIP association that is in state I1-SENT and that is
associated with the HITs in the R1). Unless the I1 was
sent in opportunistic mode (see <xref target="op_mode"
/>), the IP addresses in the received R1 packet SHOULD be
ignored and, when looking up the right HIP association,
the received R1 SHOULD be matched against the
associations using only the HITs. If a match exists, the
system should process the R1 as described below.
</t>
<t>
Otherwise, if the system is in any other state than
I1-SENT or I2-SENT with respect to the HITs included in
the R1, it SHOULD silently drop the R1 and remain in the
current state.
</t>
<t>
If the HIP association state is I1-SENT or I2-SENT, the
received Initiator's HIT MUST correspond to the HIT used
in the original, and the I1 and the Responder's HIT MUST
correspond to the one used, unless the I1 contained a
NULL HIT.
</t>
<t>
The system SHOULD validate the R1 signature before
applying further packet processing, according to <xref
target="HIP_SIGNATURE_2" />.
</t>
<t>
If the HIP association state is I1-SENT, and multiple
valid R1s are present, the system MUST select from among
the R1s with the largest R1 generation counter.
</t>
<!--TH: Changed the SHOULD in the previous section to MUST
because otherwise, an attacker could replay old R1s
with an outdated HIT_SUITE_LIST and force the
Initiator to abort the connection. -->
<!--TH: Added restart option for the Initiator here. Do we
need to define what an acceptable time span is?-->
<t>
The system MUST check that the Initiator HIT Suite is
contained in the HIT_SUITE_LIST parameter in the R1
packet (i.e., the Initiator's HIT Suite is supported by the
Responder). If the HIT Suite is supported by the
Responder, the system proceeds normally. Otherwise, the
system MAY stay in state I1-sent and restart the BEX by
sending a new I1 packet with a Initiator HIT that is
supported by the Responder and hence is contained in the
HIT_SUITE_LIST in the R1 packet. The system MAY abort
the BEX if no suitable source HIT is available. The
system SHOULD wait for acceptable time span to allow
further R1 packets with higher R1 generation counters to
arrive before restarting or aborting the BEX.
</t>
<t>
The system MUST check that the DH Group ID in the DH
parameter in the R1 matches the first DH Suite ID in the
Responder's DH_GROUP_LIST in the R1 that was also
contained in the Initiator's DH_GROUP_LIST in the I1. If
the two DH Group ID of the DH parameter does not express
the Responder's best choice, the Initiator can conclude
that the DH_GROUP_LIST in the I1 was adversely modified.
In such case, the Initiator MAY send a new I1 packet,
however, it SHOULD not change its preference in the
DH_GROUP_LIST in the new I1. Alternatively, the
Initiator MAY abort the HIP exchange.
</t>
<t>
If the HIP association state is I2-SENT, the system MAY
reenter state I1-SENT and process the received R1 if it
has a larger R1 generation counter than the R1 responded
to previously.
</t>
<t>
The R1 packet may have the A bit set -- in this case,
the system MAY choose to refuse it by dropping the R1 and
returning to state UNASSOCIATED. The system SHOULD consider
dropping the R1 only if it used a NULL HIT in I1. If the
A bit is set, the Responder's HIT is anonymous and should
not be stored.
</t>
<t>
The system SHOULD attempt to validate the HIT against the
received Host Identity by using the received Host
Identity to construct a HIT and verify that it matches
the Sender's HIT.
</t>
<t>
The system MUST store the received R1 generation counter
for future reference.
</t>
<t>
The system attempts to solve the puzzle in R1. The
system MUST terminate the search after exceeding the
remaining lifetime of the puzzle. If the puzzle is not
successfully solved, the implementation may either resend
I1 within the retry bounds or abandon the HIP exchange.
</t>
<t>
The system computes standard Diffie-Hellman keying
material according to the public value and Group ID
provided in the DIFFIE_HELLMAN parameter. The
Diffie-Hellman keying material Kij is used for key
extraction as specified in <xref target="keymat" />. If
the received Diffie-Hellman Group ID is not supported,
the implementation may either resend I1 within the retry
bounds or abandon the HIP exchange.
</t>
<t>
The system selects the HIP_CIPHER ID from the choices
presented in the R1 packet and uses the selected values
subsequently when generating and using encryption keys,
and when sending the I2. If the proposed alternatives
are not acceptable to the system, it may either resend I1
within the retry bounds or abandon the HIP exchange.
</t>
<t>
The system initializes the remaining variables in the
associated state, including Update ID counters.
</t>
<t>
The system prepares and sends an I2, as described in
<xref target="I2" />.
</t>
<t>
The system SHOULD start a timer whose timeout value
should be larger than the worst-case anticipated RTT, and
MUST increment a timeout counter associated with the I2.
The sender SHOULD retransmit the I2 upon a timeout and
restart the timer, up to a maximum of I2_RETRIES_MAX
tries.
</t>
<t>
If the system is in state I1-SENT, it shall transition
to state I2-SENT. If the system is in any other state,
it remains in the current state.
</t>
</list>
</t>
<section title="Handling Malformed Messages">
<t>
If an implementation receives a malformed R1 message, it
MUST silently drop the packet. Sending a NOTIFY or ICMP
would not help, as the sender of the R1 typically doesn't
have any state. An implementation SHOULD wait for some
more time for a possibly good R1, after which it MAY try
again by sending a new I1 packet.
</t>
</section>
</section>
<section anchor="ini2" title="Processing Incoming I2 Packets">
<t>
Upon receipt of an I2, the system MAY perform initial checks
to determine whether the I2 corresponds to a recent R1 that
has been sent out, if the Responder keeps such state. For
example, the sender could check whether the I2 is from an
address or HIT that has recently received an R1 from it. The
R1 may have had Opaque data included that was echoed back in
the I2. If the I2 is considered to be suspect, it MAY be
silently discarded by the system.
</t>
<t>
Otherwise, the HIP implementation SHOULD process the I2.
This includes validation of the puzzle solution, generating
the Diffie-Hellman key, decrypting the Initiator's Host
Identity, verifying the signature, creating state, and
finally sending an R2.
</t>
<t>
The following steps define the conceptual processing rules
for responding to an I2 packet:
<list style="numbers">
<t>
The system MAY perform checks to verify that the I2
corresponds to a recently sent R1. Such checks are
implementation dependent. See <xref target="resp-cookie"
/> for a description of an example implementation.
</t>
<t>
The system MUST check that the Responder's HIT
corresponds to one of its own HITs.
</t>
<t>
The system MUST further check that the Initiator's HIT
Suite is supported. The Responder SHOULD drop I2 packets
with unsupported Initiator HITs silently.
</t>
<t>
If the system's state machine is in the R2-SENT state,
the system MAY check if the newly received I2 is similar
to the one that triggered moving to R2-SENT. If so, it
MAY retransmit a previously sent R2, reset the R2-SENT
timer, and the state machine stays in R2-SENT.
</t>
<t>
If the system's state machine is in the I2-SENT state,
the system makes a comparison between its local and
sender's HITs (similarly as in <xref target="keymat" />).
If the local HIT is smaller than the sender's HIT, it
should drop the I2 packet, use the peer Diffie-Hellman
key and nonce I from the R1 packet received earlier, and
get the local Diffie-Hellman key and nonce J from the I2
packet sent to the peer earlier. Otherwise, the system
should process the received I2 packet and drop any
previously derived Diffie-Hellman keying material Kij it
might have formed upon sending the I2 previously. The
peer Diffie-Hellman key and the nonce J are taken from
the just arrived I2 packet. The local Diffie-Hellman key
and the nonce I are the ones that were earlier sent in
the R1 packet.
</t>
<t>
If the system's state machine is in the I1-SENT state,
and the HITs in the I2 match those used in the previously
sent I1, the system uses this received I2 as the basis
for the HIP association it was trying to form, and stops
retransmitting I1 (provided that the I2 passes the below
additional checks).
</t>
<t>
If the system's state machine is in any other state than
R2-SENT, the system SHOULD check that the echoed R1
generation counter in I2 is within the acceptable range.
Implementations MUST accept puzzles from the current
generation and MAY accept puzzles from earlier
generations. If the newly received I2 is outside the
accepted range, the I2 is stale (perhaps replayed) and
SHOULD be dropped.
</t>
<t>
The system MUST validate the solution to the puzzle by
computing the hash described in <xref target="I2" /> using
the same RHASH algorithm.
</t>
<t>
The I2 MUST have a single value in the HIP_CIPHER
parameter, which MUST match one of the values offered
to the Initiator in the R1 packet.
</t>
<t>
The system must derive Diffie-Hellman keying material Kij
based on the public value and Group ID in the
DIFFIE_HELLMAN parameter. This key is used to derive the
HIP association keys, as described in <xref
target="keymat" />. If the Diffie-Hellman Group ID is
unsupported, the I2 packet is silently dropped.
</t>
<t>
The encrypted HOST_ID is decrypted by the Initiator
encryption key defined in <xref target="keymat" />. If
the decrypted data is not a HOST_ID parameter, the I2
packet is silently dropped.
</t>
<t>
The implementation SHOULD also verify that the
Initiator's HIT in the I2 corresponds to the Host
Identity sent in the I2. (Note: some middleboxes may not
able to make this verification.)
</t>
<t>
The system MUST verify the HMAC according to the
procedures in <xref target="HIP_MAC" />.
</t>
<t>
The system MUST verify the HIP_SIGNATURE according to
<xref target="hip-signature" /> and <xref target="I2"
/>.
</t>
<t>
If the checks above are valid, then the system proceeds
with further I2 processing; otherwise, it discards the I2
and its state machine remains in the same state.
</t>
<t>
The I2 packet may have the A bit set -- in this case, the
system MAY choose to refuse it by dropping the I2 and the
state machine returns to state UNASSOCIATED. If the A
bit is set, the Initiator's HIT is anonymous and should
not be stored.
</t>
<t>
The system initializes the remaining variables in the
associated state, including Update ID counters.
</t>
<t>
Upon successful processing of an I2 when the system's
state machine is in state UNASSOCIATED, I1-SENT, I2-SENT,
or R2-SENT, an R2 is sent and the system's state machine
transitions to state R2-SENT.
</t>
<t>
Upon successful processing of an I2 when the system's
state machine is in state ESTABLISHED, the old HIP
association is dropped and a new one is installed, an R2
is sent, and the system's state machine transitions to
R2-SENT.
</t>
<t>
Upon the system's state machine transitioning to R2-SENT,
the system starts a timer. The state machine transitions
to ESTABLISHED if some data has been received on the
incoming HIP association, or an UPDATE packet has been
received (or some other packet that indicates that the
peer system's state machine has moved to ESTABLISHED).
If the timer expires (allowing for maximal
retransmissions of I2s), the state machine transitions to
ESTABLISHED.
</t>
</list>
</t>
<section title="Handling Malformed Messages">
<t>
If an implementation receives a malformed I2 message, the
behavior SHOULD depend on how many checks the message has
already passed. If the puzzle solution in the message has
already been checked, the implementation SHOULD report the
error by responding with a NOTIFY packet. Otherwise, the
implementation MAY respond with an ICMP message as defined
in <xref target="ICMP" />.
</t>
</section>
</section>
<section anchor="inc_r2" title="Processing Incoming R2 Packets">
<t>
An R2 received in states UNASSOCIATED, I1-SENT, or
ESTABLISHED results in the R2 being dropped and the state
machine staying in the same state. If an R2 is received in
state I2-SENT, it SHOULD be processed.
</t>
<t>
The following steps define the conceptual processing rules
for an incoming R2 packet:
<list style="numbers">
<t>
The system MUST verify that the HITs in use correspond to
the HITs that were received in the R1.
</t>
<t>
The system MUST verify the HIP_MAC_2 according to the
procedures in <xref target="HIP_MAC_2" />.
</t>
<t>
The system MUST verify the HIP signature according to the
procedures in <xref target="hip-signature" />.
</t>
<t>
If any of the checks above fail, there is a high
probability of an ongoing man-in-the-middle or other
security attack. The system SHOULD act accordingly, based
on its local policy.
</t>
<t>
If the system is in any other state than I2-SENT, the
R2 is silently dropped.
</t>
<t>
Upon successful processing of the R2, the state machine
moves to state ESTABLISHED.
</t>
</list>
</t>
</section>
<section anchor="send_upd" title="Sending UPDATE Packets">
<t>
A host sends an UPDATE packet when it wants to update some
information related to a HIP association. There are a number
of likely situations, e.g., mobility management and rekeying
of an existing ESP Security Association. The following
paragraphs define the conceptual rules for sending an UPDATE
packet to the peer. Additional steps can be defined in other
documents where the UPDATE packet is used.
</t>
<t>
The system first determines whether there are any outstanding
UPDATE messages that may conflict with the new UPDATE message
under consideration. When multiple UPDATEs are outstanding
(not yet acknowledged), the sender must assume that such
UPDATEs may be processed in an arbitrary order. Therefore,
any new UPDATEs that depend on a previous outstanding UPDATE
being successfully received and acknowledged MUST be
postponed until reception of the necessary ACK(s) occurs.
One way to prevent any conflicts is to only allow one
outstanding UPDATE at a time. However, allowing multiple
UPDATEs may improve the performance of mobility and
multihoming protocols.
</t>
<t>
The following steps define the conceptual processing rules
for sending UPDATE packets.
</t>
<t>
<list style="numbers">
<t>
The first UPDATE packet is sent with Update ID of zero.
Otherwise, the system increments its own Update ID value
by one before continuing the below steps.
</t>
<t>
The system creates an UPDATE packet that contains a SEQ
parameter with the current value of Update ID. The
UPDATE packet may also include an ACK of the peer's
Update ID found in a received UPDATE SEQ parameter, if
any.
</t>
<t>
The system sends the created UPDATE packet and starts an
UPDATE timer. The default value for the timer is 2 *
RTT estimate. If multiple UPDATEs are outstanding,
multiple timers are in effect.
</t>
<t>
If the UPDATE timer expires, the UPDATE is resent. The
UPDATE can be resent UPDATE_RETRY_MAX times. The UPDATE
timer SHOULD be exponentially backed off for subsequent
retransmissions. If no acknowledgment is received from
the peer after UPDATE_RETRY_MAX times, the HIP
association is considered to be broken and the state
machine should move from state ESTABLISHED to state
CLOSING as depicted in <xref target="hipstates" />. The
UPDATE timer is cancelled upon receiving an ACK from the
peer that acknowledges receipt of the UPDATE.
</t>
</list>
</t>
</section>
<section title="Receiving UPDATE Packets">
<t>
When a system receives an UPDATE packet, its processing
depends on the state of the HIP association and the presence
and values of the SEQ and ACK parameters. Typically, an
UPDATE message also carries optional parameters whose
handling is defined in separate documents.
</t>
<t>
For each association, the peer's next expected in-sequence
Update ID ("peer Update ID") is stored. Initially, this
value is zero. Update ID comparisons of "less than" and
"greater than" are performed with respect to a circular
sequence number space.
</t>
<t>
The sender may send multiple outstanding UPDATE messages.
These messages are processed in the order in which they are
received at the receiver (i.e., no resequencing is
performed). When processing UPDATEs out-of-order, the
receiver MUST keep track of which UPDATEs were previously
processed, so that duplicates or retransmissions are ACKed
and not reprocessed. A receiver MAY choose to define a
receive window of Update IDs that it is willing to process at
any given time, and discard received UPDATEs falling outside
of that window.
</t>
<t>
The following steps define the conceptual processing rules
for receiving UPDATE packets.
</t>
<t>
<list style="numbers">
<t>
If there is no corresponding HIP association, the
implementation MAY reply with an ICMP Parameter Problem,
as specified in <xref target="non-existing-hip" />.
</t>
<t>
If the association is in the ESTABLISHED state and the
SEQ (but not ACK) parameter is present, the UPDATE is
processed and replied to as described in <xref
target="upd_seq" />.
</t>
<t>
If the association is in the ESTABLISHED state and the
ACK (but not SEQ) parameter is present, the UPDATE is
processed as described in <xref target="upd_ack" />.
</t>
<t>
If the association is in the ESTABLISHED state and there
is both an ACK and SEQ in the UPDATE, the ACK is first
processed as described in <xref target="upd_ack" />, and
then the rest of the UPDATE is processed as described in
<xref target="upd_seq" />.
</t>
</list>
</t>
<section anchor="upd_seq"
title="Handling a SEQ Parameter in a Received UPDATE Message">
<t>
The following steps define the conceptual processing rules
for handling a SEQ parameter in a received UPDATE packet.
</t>
<t>
<list style="numbers">
<t>
If the Update ID in the received SEQ is not the next
in the sequence of Update IDs and is greater than the
receiver's window for new UPDATEs, the packet MUST be
dropped.
</t>
<t>
If the Update ID in the received SEQ corresponds to an
UPDATE that has recently been processed, the packet is
treated as a retransmission. The HIP_MAC verification
(next step) MUST NOT be skipped. (A byte-by-byte
comparison of the received and a stored packet would be
OK, though.) It is recommended that a host cache
UPDATE packets sent with ACKs to avoid the cost of
generating a new ACK packet to respond to a replayed
UPDATE. The system MUST acknowledge, again, such
(apparent) UPDATE message retransmissions but SHOULD
also consider rate-limiting such retransmission
responses to guard against replay attacks.
</t>
<t>
The system MUST verify the HIP_MAC in the UPDATE
packet. If the verification fails, the packet MUST be
dropped.
</t>
<t>
The system MAY verify the SIGNATURE in the UPDATE
packet. If the verification fails, the packet SHOULD
be dropped and an error message logged.
</t>
<t>
If a new SEQ parameter is being processed, the
parameters in the UPDATE are then processed. The
system MUST record the Update ID in the received SEQ
parameter, for replay protection.
</t>
<t>
An UPDATE acknowledgment packet with ACK parameter is
prepared and sent to the peer. This ACK parameter may
be included in a separate UPDATE or piggybacked in an
UPDATE with SEQ parameter, as described in <xref
target="UPDATE" />. The ACK parameter MAY acknowledge
more than one of the peer's Update IDs.
</t>
</list>
</t>
</section>
<section anchor="upd_ack"
title="Handling an ACK Parameter in a Received UPDATE Packet">
<t>
The following steps define the conceptual processing rules
for handling an ACK parameter in a received UPDATE packet.
</t>
<t>
<list style="numbers">
<t>
The sequence number reported in the ACK must match
with an earlier sent UPDATE packet that has not
already been acknowledged. If no match is found or if
the ACK does not acknowledge a new UPDATE, the packet
MUST either be dropped if no SEQ parameter is present,
or the processing steps in <xref target="upd_seq" />
are followed.
</t>
<t>
The system MUST verify the HIP_MAC in the UPDATE
packet. If the verification fails, the packet MUST be
dropped.
</t>
<t>
The system MAY verify the SIGNATURE in the UPDATE
packet. If the verification fails, the packet SHOULD
be dropped and an error message logged.
</t>
<t>
The corresponding UPDATE timer is stopped (see <xref
target="send_upd" />) so that the now acknowledged
UPDATE is no longer retransmitted. If multiple UPDATEs
are newly acknowledged, multiple timers are stopped.
</t>
</list>
</t>
</section>
</section>
<section title="Processing NOTIFY Packets">
<t>
Processing NOTIFY packets is OPTIONAL. If processed, any
errors in a received NOTIFICATION parameter SHOULD be logged.
Received errors MUST be considered only as informational, and
the receiver SHOULD NOT change its HIP state (<xref
target="states" />) purely based on the received NOTIFY
message.
</t>
</section>
<section title="Processing CLOSE Packets">
<t>
When the host receives a CLOSE message, it responds with a
CLOSE_ACK message and moves to CLOSED state. (The
authenticity of the CLOSE message is verified using both
HIP_MAC and SIGNATURE). This processing applies whether or
not the HIP association state is CLOSING in order to handle
CLOSE messages from both ends that cross in flight.
</t>
<t>
The HIP association is not discarded before the host moves
from the UNASSOCIATED state.
</t>
<t>
Once the closing process has started, any need to send data
packets will trigger creating and establishing of a new HIP
association, starting with sending an I1.
</t>
<t>
If there is no corresponding HIP association, the CLOSE packet
is dropped.
</t>
</section>
<section title="Processing CLOSE_ACK Packets">
<t>
When a host receives a CLOSE_ACK message, it verifies that it
is in CLOSING or CLOSED state and that the CLOSE_ACK was in
response to the CLOSE (using the included
ECHO_RESPONSE_SIGNED in response to the sent
ECHO_REQUEST_SIGNED).
</t>
<t>
The CLOSE_ACK uses HIP_MAC and SIGNATURE for verification.
The state is discarded when the state changes to UNASSOCIATED
and, after that, the host MAY respond with an ICMP Parameter
Problem to an incoming CLOSE message (see <xref
target="non-existing-hip" />).
</t>
</section>
<section title="Handling State Loss">
<t>
In the case of system crash and unanticipated state loss, the
system SHOULD delete the corresponding HIP state, including
the keying material. That is, the state SHOULD NOT be stored
on stable storage. If the implementation does drop the state
(as RECOMMENDED), it MUST also drop the peer's R1 generation
counter value, unless a local policy explicitly defines that
the value of that particular host is stored. An
implementation MUST NOT store R1 generation counters by
default, but storing R1 generation counter values, if done,
MUST be configured by explicit HITs.
</t>
</section>
</section>
<section anchor="sec-policy" title="HIP Policies">
<t>
There are a number of variables that will influence the HIP
exchanges that each host must support. All HIP implementations
MUST support more than one simultaneous HI, at least one of
which SHOULD be reserved for anonymous usage. Although
anonymous HIs will be rarely used as Responders' HIs, they will
be common for Initiators. Support for more than two HIs is
RECOMMENDED.
</t>
<t>
Many Initiators would want to use a different HI for different
Responders. The implementations SHOULD provide for an ACL of
Initiator's HIT to Responder's HIT. This ACL SHOULD also
include preferred transform and local lifetimes.
</t>
<t>
The value of K used in the HIP R1 packet can also vary by
policy. K should never be greater than 20, but for trusted
partners it could be as low as 0.
</t>
<t>
Responders would need a similar ACL, representing which hosts
they accept HIP exchanges, and the preferred transform and
local lifetimes. Wildcarding SHOULD be supported for this ACL
also.
</t>
</section>
<section anchor="sec-considerations" title="Security Considerations">
<t>
HIP is designed to provide secure authentication of hosts. HIP
also attempts to limit the exposure of the host to various
denial-of-service and man-in-the-middle (MitM) attacks. In so
doing, HIP itself is subject to its own DoS and MitM attacks
that potentially could be more damaging to a host's ability to
conduct business as usual.
</t>
<t>
Denial-of-service attacks often take advantage of the cost of
start of state for a protocol on the Responder compared to the
'cheapness' on the Initiator. HIP makes no attempt to increase
the cost of the start of state on the Initiator, but makes an
effort to reduce the cost to the Responder. This is done by
having the Responder start the 3-way exchange instead of the
Initiator, making the HIP protocol 4 packets long. In doing
this, packet 2 becomes a 'stock' packet that the Responder MAY
use many times, until some Initiator has provided a valid
response to such an R1 packet. During an I1 storm, the host
may reuse the same DH value also even if some Initiator has
provided a valid response using that particular DH value.
However, such behavior is discouraged and should be avoided.
Using the same Diffie-Hellman values and random puzzle #I value
has some risks. This risk needs to be balanced against a
potential storm of HIP I1 packets.
</t>
<t>
This shifting of the start of state cost to the Initiator in
creating the I2 HIP packet, presents another DoS attack. The
attacker spoofs the I1 HIP packet and the Responder sends out
the R1 HIP packet. This could conceivably tie up the
'Initiator' with evaluating the R1 HIP packet, and creating the
I2 HIP packet. The defense against this attack is to simply
ignore any R1 packet where a corresponding I1 was not sent.
</t>
<t>
A second form of DoS attack arrives in the I2 HIP packet. Once
the attacking Initiator has solved the puzzle, it can send
packets with spoofed IP source addresses with either an invalid
encrypted HIP payload component or a bad HIP signature. This
would take resources in the Responder's part to reach the point
to discover that the I2 packet cannot be completely processed.
The defense against this attack is after N bad I2 packets, the
Responder would discard any I2s that contain the given
Initiator HIT. This will shut down the attack. The attacker
would have to request another R1 and use that to launch a new
attack. The Responder could up the value of K while under
attack. On the downside, valid I2s might get dropped too.
</t>
<t>
A third form of DoS attack is emulating the restart of state
after a reboot of one of the partners. A restarting host would
send an I1 to a peer, which would respond with an R1 even if it
were in the ESTABLISHED state. If the I1 were spoofed, the
resulting R1 would be received unexpectedly by the spoofed host
and would be dropped, as in the first case above.
</t>
<t>
A fourth form of DoS attack is emulating the end of state. HIP
relies on timers plus a CLOSE/CLOSE_ACK handshake to explicitly
signal the end of a HIP association. Because both CLOSE and
CLOSE_ACK messages contain an HIP_MAC, an outsider cannot close
a connection. The presence of an additional SIGNATURE allows
middleboxes to inspect these messages and discard the
associated state (for e.g., firewalling, SPI-based NATing,
etc.). However, the optional behavior of replying to CLOSE
with an ICMP Parameter Problem packet (as described in <xref
target="non-existing-hip" />) might allow an IP spoofer sending
CLOSE messages to launch reflection attacks.
</t>
<t>
A fifth form of DoS attack is replaying R1s to cause the
Initiator to solve stale puzzles and become out of
synchronization with the Responder. The R1 generation counter
is a monotonically increasing counter designed to protect
against this attack, as described in <xref target="hip-replay"
/>.
</t>
<t>
Man-in-the-middle attacks are difficult to defend against,
without third-party authentication. A skillful MitM could
easily handle all parts of HIP, but HIP indirectly provides the
following protection from a MitM attack. If the Responder's HI
is retrieved from a signed DNS zone, a certificate, or through
some other secure means, the Initiator can use this to validate
the R1 HIP packet.
</t>
<t>
Likewise, if the Initiator's HI is in a secure DNS zone, a
trusted certificate, or otherwise securely available, the
Responder can retrieve the HI (after having got the I2 HIP
packet) and verify that the HI indeed can be trusted. However,
since an Initiator may choose to use an anonymous HI, it
knowingly risks a MitM attack. The Responder may choose not to
accept a HIP exchange with an anonymous Initiator.
</t>
<t>
The HIP Opportunistic Mode concept has been introduced in this
document, but this document does not specify what the semantics
of such a connection setup are for applications. There are
certain concerns with opportunistic mode, as discussed in <xref
target="op_mode" />.
</t>
<t>
NOTIFY messages are used only for informational purposes and
they are unacknowledged. A HIP implementation cannot rely
solely on the information received in a NOTIFY message because
the packet may have been replayed. It SHOULD NOT change any
state information based purely on a received NOTIFY message.
</t>
<t>
Since not all hosts will ever support HIP, ICMP 'Destination
Protocol Unreachable' messages are to be expected and present a
DoS attack. Against an Initiator, the attack would look like
the Responder does not support HIP, but shortly after receiving
the ICMP message, the Initiator would receive a valid R1 HIP
packet. Thus, to protect from this attack, an Initiator should
not react to an ICMP message until a reasonable delta time to
get the real Responder's R1 HIP packet. A similar attack
against the Responder is more involved. Normally, if an I1
message received by a Responder was a bogus one sent by an
attacker, the Responder may receive an ICMP message from the IP
address the R1 message was sent to. However, a sophisticated
attacker can try to take advantage of such a behavior and try
to break up the HIP exchange by sending such an ICMP message to
the Responder before the Initiator has a chance to send a valid
I2 message. Hence, the Responder SHOULD NOT act on such an
ICMP message. Especially, it SHOULD NOT remove any minimal
state created when it sent the R1 HIP packet (if it did create
one), but wait for either a valid I2 HIP packet or the natural
timeout (that is, if R1 packets are tracked at all). Likewise,
the Initiator should ignore any ICMP message while waiting for
an R2 HIP packet, and should delete any pending state only
after a natural timeout.
</t>
</section>
<section anchor="iana" title="IANA Considerations">
<!--TH we create a new namespace with the HIT suites - this should be
mentioned here. -->
<t>
IANA has reserved protocol number 139 for the Host Identity Protocol.
</t>
<t>
This document defines a new 128-bit value under the CGA Message
Type namespace <xref target="RFC3972"/>, 0xF0EF F02F BFF4 3D0F
E793 0C3C 6E61 74EA, to be used for HIT generation as specified
in ORCHID <xref target="RFC4843-bis" />.
</t>
<t>
This document also creates a set of new namespaces. These are
described below.
</t>
<t>
<list style='hanging'>
<t hangText='Packet Type'><vspace blankLines='1'/>
The 7-bit Packet Type field in a HIP protocol packet
describes the type of a HIP protocol message. It is defined
in <xref target='ssec-payload'/>. The current values are
defined in Sections <xref target='I1' format="counter"/>
through <xref target='CLOSE_ACK' format="counter"/>.
</t>
<t>
New values are assigned through <xref target='RFC2434'>IETF
Consensus</xref>.
</t>
<t hangText='HIP Version'><vspace blankLines='1'/>
The four-bit Version field in a HIP protocol packet
describes the version of the HIP protocol. It is defined in
<xref target='ssec-payload'/>. The currently defined values
are 1 and 2. The version of this document is 2. New values
are assigned through IETF Consensus.</t>
<t hangText='HIT Suite'><vspace blankLines='1'/>
The four-bit HIT Suite ID uses the OGA field in the ORCHID
to express the type of the HIT. This document defines two
HIT Suites.
<vspace blankLines='1'/>
The HIT Suite ID is also carried in the four higher-order
bits of the ID field in the HIT_SUITE_LIST parameter. The
four lower-order bits are reserved for future extensions of
the HIT Suite ID space beyond 16 values.
<vspace blankLines='1'/>
At the time being, the HIT Suite uses only four bits
because these bits have to be carried in the HIT. Using
more bits for the HIT Suite ID reduces the cryptographic
strength of the HIT. HIT Suite IDs must be allocated
carefully to avoid namespace exhaustion. Moreover,
deprecated IDs should be reused after an appropriate time
span. If 16 Suite IDs prove insufficient and more HIT Suite
IDs are needed concurrently, more bits can be used for the
HIT Suite ID by using one HIT Suite ID (0) to indicate that
more bits should be used. The HIT_SUITE_LIST parameter
already supports 8-bit HIT Suite IDs, should longer IDs be
needed. Possible extensions of the HIT Suite ID space to
eight-bit and new HIT Suite IDs are defined through IETF
Consensus.
</t>
<!--TH: I have to name the proper number of HIT suites
here.-->
<t hangText='Parameter Type'><vspace blankLines='1'/>
The 16-bit Type field in a HIP parameter describes the type
of the parameter. It is defined in <xref
target='tlvformat'/>. The current values are defined in
Sections <xref target='r1_counter' format="counter"/>
through <xref target='echo_response_unsigned'
format="counter"/>.
<vspace blankLines='1'/>
With the exception of the assigned Type codes, the Type
codes 0 through 1023 and 61440 through 65535 are reserved
for future base protocol extensions, and are assigned
through IETF Consensus.
<vspace blankLines='1'/>
The Type codes 32768 through 49141 are reserved for
experimentation. Types SHOULD be selected in a random
fashion from this range, thereby reducing the probability
of collisions. A method employing genuine randomness (such
as flipping a coin) SHOULD be used.
<vspace blankLines='1'/>
All other Type codes are assigned through First Come First
Served, with <xref target='RFC2434'>Specification Required
</xref>.
</t>
<t hangText='Group ID'><vspace blankLines='1'/>
The eight-bit Group ID values appear in the DIFFIE_HELLMAN
parameter and the DH_GROUP_LIST parameter and are defined in
<xref target='diffie_hellman'/>.
New values either from the reserved or unassigned space are
assigned through IETF Consensus.</t>
<t hangText='HIP Cipher ID'><vspace blankLines='1'/>
The 16-bit Cipher ID values in a HIP_CIPHER parameter are defined in
<xref target='hip_cipher'/>.
New values either from the reserved or unassigned space are
assigned through IETF Consensus.</t>
<t hangText='DI-Type'><vspace blankLines='1'/>
The four-bit DI-Type values in a HOST_ID parameter are
defined in <xref target='host-id'/>. New values are
assigned through IETF Consensus.</t>
<t hangText='Notify Message Type'><vspace blankLines='1'/>
The 16-bit Notify Message Type values in a NOTIFICATION
parameter are defined in <xref target='notify'/>.
</t>
<t>
Notify Message Type values 1-10 are used for informing
about errors in packet structures, values 11-20 for
informing about problems in parameters containing
cryptographic related material, values 21-30 for informing
about problems in authentication or packet integrity
verification. Parameter numbers above 30 can be used for
informing about other types of errors or events. Values
51-8191 are error types reserved to be allocated by IANA.
Values 8192-16383 are error types for experimentation.
Values 16385-40959 are status types to be allocated by
IANA, and values 40960-65535 are status types for
experimentation. New values in ranges 51-8191 and
16385-40959 are assigned through First Come First Served,
with Specification Required.
</t>
</list>
</t>
</section>
<section title="Acknowledgments">
<t>
The drive to create HIP came to being after attending the
MALLOC meeting at the 43rd IETF meeting. Baiju Patel and
Hilarie Orman really gave the original author, Bob Moskowitz,
the assist to get HIP beyond 5 paragraphs of ideas. It has
matured considerably since the early versions thanks to
extensive input from IETFers. Most importantly, its design
goals are articulated and are different from other efforts in
this direction. Particular mention goes to the members of the
NameSpace Research Group of the IRTF. Noel Chiappa provided
valuable input at early stages of discussions about identifier
handling and Keith Moore the impetus to provide resolvability.
Steve Deering provided encouragement to keep working, as a
solid proposal can act as a proof of ideas for a research
group.
</t>
<t>
Many others contributed; extensive security tips were provided
by Steve Bellovin. Rob Austein kept the DNS parts on track.
Paul Kocher taught Bob Moskowitz how to make the puzzle
exchange expensive for the Initiator to respond, but easy for
the Responder to validate. Bill Sommerfeld supplied the
Birthday concept, which later evolved into the R1 generation
counter, to simplify reboot management. Erik Nordmark supplied
the CLOSE-mechanism for closing connections. Rodney Thayer and
Hugh Daniels provided extensive feedback. In the early times
of this document, John Gilmore kept Bob Moskowitz challenged to
provide something of value.
</t>
<t>
During the later stages of this document, when the editing
baton was transferred to Pekka Nikander, the input from the
early implementors was invaluable. Without having actual
implementations, this document would not be on the level it is
now.
</t>
<t>
In the usual IETF fashion, a large number of people have
contributed to the actual text or ideas. The list of these
people include Jeff Ahrenholz, Francis Dupont, Derek Fawcus,
George Gross, Andrew McGregor, Julien Laganier, Miika Komu,
Mika Kousa, Jan Melen, Henrik Petander, Michael Richardson,
Rene Hummen, Tim Shepard, Jorma Wall, and Jukka Ylitalo. Our
apologies to anyone whose name is missing.
</t>
<t>
Once the HIP Working Group was founded in early 2004, a number
of changes were introduced through the working group process.
Most notably, the original document was split in two, one
containing the base exchange and the other one defining how to
use ESP. Some modifications to the protocol proposed by Aura,
et al., <xref target="AUR03" /> were added at a later stage.
</t>
</section>
</middle>
<back>
<references title="Normative References">
&RFC0768;
&RFC1035;
&RFC2119;
&RFC2404;
&RFC2410;
&RFC2451;
&RFC2460;
&RFC2463;
&RFC2536;
&RFC2898;
&RFC3110;
&RFC3484;
&RFC3526;
&RFC3602;
&RFC3972;
&RFC4034;
&RFC4307;
&RFC4843-bis; <!-- was RFC4843 -->
&RFC4282;
&RFC4753;
&RFC4868;
&RFC5202;
&RFC5201;
&RFC5702;
&RFC5869;
&fundamental-ecc;
&FIPS95;
&FIPS180-2;
</references>
<references title="Informative References">
&RFC0792;
&RFC4306;
&RFC2434;
&rfc4423-bis; <!-- was RFC4423 -->
&RFC5533;
&RFC5338;
&btns-c-api;
&RFC5206;
&RFC5205;
&RFC5204;
<reference anchor="AUR03">
<front>
<title>Analysis of the HIP Base Exchange Protocol </title>
<author initials="T" surname="Aura"
fullname="Tuomas Aura">
<organization>Microsoft Research</organization>
</author>
<author initials="A" surname="Nagarajan"
fullname="Aarthi Nagarajan">
<organization>Technische Universitat Hamburg</organization>
</author>
<author initials="A" surname="Gurtov"
fullname="Andrei Gurtov">
<organization>Helsinki Institute for Information Technology
</organization>
</author>
<date month="July" year="2003" />
</front>
<seriesInfo name="in Proceedings of"
value="10th Australasian Conference on Information Security and
Privacy" />
</reference>
<reference anchor="KRA03">
<front>
<title>SIGMA: The 'SIGn-and-MAc' Approach to Authenticated
Diffie-Hellman and Its Use in the IKE-Protocols</title>
<author initials="H" surname="Krawczyk"
fullname="Hugo Krawczyk">
<organization></organization>
</author>
<date month="August" year="2003" />
</front>
<seriesInfo name="in Proceedings of"
value="CRYPTO 2003, pages 400-425" />
</reference>
<reference anchor="CRO03">
<front>
<title>Denial of Service via Algorithmic Complexity
Attacks</title>
<author initials="SA" surname="Crosby"
fullname="Scott A. Crosby">
<organization>Rice University</organization>
</author>
<author initials="DS" surname="Wallach"
fullname="Dan S. Wallach">
<organization>Rice University</organization>
</author>
<date month="August" day="4-8" year="2003" />
</front>
<seriesInfo name="in Proceedings of"
value="Usenix Security Symposium 2003" />
<seriesInfo name="" value="Washington, DC." />
</reference>
&FIPS197;
<reference anchor="DIF76">
<front>
<title>New Directions in Cryptography</title>
<author initials="W" surname="Diffie"
fullname="Whitfield Diffie">
<organization />
</author>
<author initials="M.E." surname="Hellman"
fullname="Martin E. Hellman">
<organization />
</author>
<date month="Nov" year="1976" />
</front>
<seriesInfo name="IEEE Transactions on Information Theory"
value="vol. IT-22, number 6, pages 644-654" />
</reference>
<reference anchor="KAU03">
<front>
<title>DoS protection for UDP-based protocols</title>
<author initials="C" surname="Kaufman"
fullname="C. Kaufman">
<organization />
</author>
<author initials="R" surname="Perlman"
fullname="R. Perlman">
<organization />
</author>
<author initials="B" surname="Sommerfeld"
fullname="B. Sommerfeld">
<organization />
</author>
<date month="Oct" year="2003" />
</front>
<seriesInfo name="ACM Conference on Computer and Communications Security"
value="" />
</reference>
</references>
<section anchor="resp-cookie" title="Using Responder Puzzles">
<t>
As mentioned in <xref target="hip-cookie" />, the Responder may
delay state creation and still reject most spoofed I2s by using
a number of pre-calculated R1s and a local selection function.
This appendix defines one possible implementation in detail.
The purpose of this appendix is to give the implementors an
idea on how to implement the mechanism. If the implementation
is based on this appendix, it MAY contain some local
modification that makes an attacker's task harder.
</t>
<t>
The Responder creates a secret value S, that it regenerates
periodically. The Responder needs to remember the two latest
values of S. Each time the S is regenerated, the R1
generation counter value is incremented by one.
</t>
<t>
The Responder generates a pre-signed R1 packet. The signature
for pre-generated R1s must be recalculated when the
Diffie-Hellman key is recomputed or when the R1_COUNTER value
changes due to S value regeneration.
</t>
<t>
When the Initiator sends the I1 packet for initializing a
connection, the Responder gets the HIT and IP address from the
packet, and generates an I value for the puzzle. The I value
is set to the pre-signed R1 packet.
</t>
<figure>
<artwork>
I value calculation:
I = Ltrunc( RHASH ( S | HIT-I | HIT-R | IP-I | IP-R ), n)
where n = RHASH-len/2
</artwork>
</figure>
<t>
The RHASH algorithm is the same that is used to generate
the Responder's HIT value.
</t>
<t>
From an incoming I2 packet, the Responder gets the required
information to validate the puzzle: HITs, IP addresses, and the
information of the used S value from the R1_COUNTER. Using
these values, the Responder can regenerate the I, and verify it
against the I received in the I2 packet. If the I values
match, it can verify the solution using I, J, and difficulty K.
If the I values do not match, the I2 is dropped.
</t>
<figure>
<artwork>
puzzle_check:
V := Ltrunc( RHASH( I2.I | I2.hit_i | I2.hit_r | I2.J ), K )
if V != 0, drop the packet
</artwork>
</figure>
<t>
If the puzzle solution is correct, the I and J values are
stored for later use. They are used as input material when
keying material is generated.
</t>
<t>
Keeping state about failed puzzle solutions depends on the
implementation. Although it is possible for the Responder not
to keep any state information, it still may do so to protect
itself against certain attacks (see <xref target="hip-cookie"
/>).
</t>
</section>
<section anchor="app_generhit" title="Generating a Public Key Encoding
from an HI">
<t>
The following pseudo-code illustrates the process to generate a
public key encoding from an HI for both RSA and DSA.
</t>
<t>
The symbol <spanx style="tt">:=</spanx> denotes assignment; the
symbol <spanx style="tt">+=</spanx> denotes appending. The
pseudo-function <spanx
style="tt">encode_in_network_byte_order</spanx> takes two
parameters, an integer (bignum) and a length in bytes, and
returns the integer encoded into a byte string of the given
length.
</t>
<figure>
<artwork>
switch ( HI.algorithm )
{
case RSA:
buffer := encode_in_network_byte_order ( HI.RSA.e_len,
( HI.RSA.e_len > 255 ) ? 3 : 1 )
buffer += encode_in_network_byte_order ( HI.RSA.e, HI.RSA.e_len )
buffer += encode_in_network_byte_order ( HI.RSA.n, HI.RSA.n_len )
break;
case DSA:
buffer := encode_in_network_byte_order ( HI.DSA.T , 1 )
buffer += encode_in_network_byte_order ( HI.DSA.Q , 20 )
buffer += encode_in_network_byte_order ( HI.DSA.P , 64 +
8 * HI.DSA.T )
buffer += encode_in_network_byte_order ( HI.DSA.G , 64 +
8 * HI.DSA.T )
buffer += encode_in_network_byte_order ( HI.DSA.Y , 64 +
8 * HI.DSA.T )
break;
}
</artwork>
</figure>
</section>
<section title="Example Checksums for HIP Packets">
<t>
The HIP checksum for HIP packets is specified in <xref
target="ssec-crc" />. Checksums for TCP and UDP packets
running over HIP-enabled security associations are specified in
Section 3.5. The examples below use IP addresses of
192.168.0.1 and 192.168.0.2 (and their respective
IPv4-compatible IPv6 formats), and HITs with the prefix of
2001:10 followed by zeros, followed by a decimal 1 or 2,
respectively.
</t>
<t>
The following example is defined only for testing a checksum
calculation. The address format for the IPv4-compatible IPv6
address is not a valid one, but using these IPv6 addresses when
testing an IPv6 implementation gives the same checksum output
as an IPv4 implementation with the corresponding IPv4
addresses.
</t>
<section title="IPv6 HIP Example (I1)">
<figure>
<artwork>
Source Address: ::192.168.0.1
Destination Address: ::192.168.0.2
Upper-Layer Packet Length: 40 0x28
Next Header: 139 0x8b
Payload Protocol: 59 0x3b
Header Length: 4 0x4
Packet Type: 1 0x1
Version: 1 0x1
Reserved: 1 0x1
Control: 0 0x0
Checksum: 446 0x1be
Sender's HIT : 2001:10::1
Receiver's HIT: 2001:10::2
</artwork>
</figure>
</section>
<section title="IPv4 HIP Packet (I1)">
<t>
The IPv4 checksum value for the same example I1 packet is the
same as the IPv6 checksum (since the checksums due to the
IPv4 and IPv6 pseudo-header components are the same).
</t>
</section>
<section title="TCP Segment">
<t>
Regardless of whether IPv6 or IPv4 is used, the TCP and UDP
sockets use the IPv6 pseudo-header format <xref
target="RFC2460"/>, with the HITs used in place of the IPv6
addresses.
</t>
<figure>
<artwork>
Sender's HIT: 2001:10::1
Receiver's HIT: 2001:10::2
Upper-Layer Packet Length: 20 0x14
Next Header: 6 0x06
Source port: 65500 0xffdc
Destination port: 22 0x0016
Sequence number: 1 0x00000001
Acknowledgment number: 0 0x00000000
Header length: 20 0x14
Flags: SYN 0x02
Window size: 65535 0xffff
Checksum: 28618 0x6fca
Urgent pointer: 0 0x0000
0x0000: 6000 0000 0014 0640 2001 0010 0000 0000
0x0010: 0000 0000 0000 0001 2001 0010 0000 0000
0x0020: 0000 0000 0000 0002 ffdc 0016 0000 0001
0x0030: 0000 0000 5002 ffff 6fca 0000
</artwork>
</figure>
</section>
</section>
<section anchor="ecdh-160-group" title="ECDH-160 Group">
<t>
The ECDH-160 group is rated at 80 bits strength. Once this
was considered appropriate for one year of security. Today
should be used only when the host is not powerful enough
(e.g., some PDAs) and when security requirements are low
(e.g., during normal web surfing).
</t>
<!--RM: We need the parameter values here for ECDH-160 with reference source. -->
</section>
<section anchor="hit-suites" title="HIT Suites and HIT Generation">
<t>
The HIT as an ORCHID <xref target="RFC4843-bis" /> consists of
three parts: A 28-bit prefix, a 4-bit encoding of the ORCHID
generation algorithm (OGA) and the representation of the public
key. The OGA is an index pointing to the specific algorithm by
which the public key and the 96-bit hashed encoding is
generated. The OGA is protocol specific and is to be
interpreted as defined below for all protocols that use the
same context ID as HIP. HIP groups sets of valid combinations
of signature and hash algorithms into HIT Suites. These HIT
suites are addressed by an index, which is transmitted in the
OGA field of the ORCHID.
</t>
<t>
The set of used HIT Suites will be extended to counter the
progress in computation capabilities and vulnerabilities in the
employed algorithms. The intended use of the HIT Suites is to
introduce a new HIT Suite and phase out an old one before it
becomes insecure. Since the 4-bit OGA field only permits 15
HIT Suites (the HIT Suite with ID 0 is reserved) to be used in
parallel, phased-out HIT Suites must be reused at some point.
In such a case, there will be a rollover of the HIT Suite ID
and the next newly introduced HIT Suite will start with a lower
HIT Suite index than the previoulsy introduced one. The
rollover effectively deprecates the reused HIT Suite. For a
smooth transition, the HIT Suite should be deprecated a
considerable time before the HIT Suite index is reused.
</t>
<t>
Since the number of HIT Suites is tightly limited to 16, the
HIT Suites must be assigned carefully. Hence, sets of suitable
algorithms are grouped in a HIT Suite.
</t>
<t>
The HIT Suite of the Responder's HIT determines the RHASH and
the hash function to be used for the HMAC in HIP control
packets as well as the signature algorithm family used for
generating the HI. The list of HIT Suites is defined in
<xref target="table_hit_suites" />.
</t>
<t>
The following HIT Suites are defined for HIT generation. The
input for each generation algorithm is the encoding of the HI
as defined in <xref target="gener_hit" />. The output is 96
bits long and is directly used in the ORCHID.
</t>
<texttable title="HIT Suites" anchor="table_hit_suites">
<ttcol align="right">Index</ttcol>
<ttcol align="left">Hash function</ttcol>
<ttcol align="left">Signature algorithm family</ttcol>
<ttcol align="left">Description</ttcol>
<c>0</c> <c></c> <c></c> <c>Reserved</c>
<c>1</c> <c>SHA-1</c> <c>RSA, DSA</c> <c>RSA or DSA HI hashed with SHA-1, truncated to 96 bits</c>
<c>2</c> <c>SHA-256</c> <c>ECDSA</c> <c>ECDSA HI hashed with SHA-256, truncated to 96 bits</c>
<c>3</c> <c>SHA-384</c> <c>ECDSA</c> <c>ECDSA HI hashed with SHA-384, truncated to 96 bits</c>
</texttable>
</section>
</back>
</rfc>
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