One document matched: draft-ietf-pcp-authentication-01.txt
Differences from draft-ietf-pcp-authentication-00.txt
Network Working Group M. Wasserman
Internet-Draft S. Hartman
Intended status: Experimental Painless Security
Expires: April 22, 2013 D. Zhang
Huawei
October 19, 2012
Port Control Protocol (PCP) Authentication Mechanism
draft-ietf-pcp-authentication-01.txt
Abstract
An IPv4 or IPv6 host can use the Port Control Protocol (PCP) to
flexibly manage the IP address and port mapping information on
Network Address Translators (NATs) or firewalls, to facilitate
communications with remote hosts. However, the un-controlled
generation or deletion of IP address mappings on such network devices
may cause security risks and should be avoided. In some cases the
client may need to prove that it is authorized to modify, create or
delete PCP mappings. This document proposes an in-band
authentication mechanism for PCP that can be used in those cases.
The Extensible Authentication Protocol (EAP) is used to perform
authentication between PCP devices.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 22, 2013.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Separate vs. Inline Key Management . . . . . . . . . . . . . . 5
4. Separate Key Management . . . . . . . . . . . . . . . . . . . 5
5. Protocol Details . . . . . . . . . . . . . . . . . . . . . . . 6
5.1. Session Initiation . . . . . . . . . . . . . . . . . . . . 6
5.2. Session Termination . . . . . . . . . . . . . . . . . . . 8
6. PA Security Association . . . . . . . . . . . . . . . . . . . 8
7. Packet Format . . . . . . . . . . . . . . . . . . . . . . . . 9
7.1. Authentication OpCode Format . . . . . . . . . . . . . . . 9
7.2. Nonce Option . . . . . . . . . . . . . . . . . . . . . . . 11
7.3. Authentication Tag Option . . . . . . . . . . . . . . . . 11
7.4. EAP Payload Option . . . . . . . . . . . . . . . . . . . . 12
7.5. PRF Option . . . . . . . . . . . . . . . . . . . . . . . . 12
7.6. Hash Algorithm Option . . . . . . . . . . . . . . . . . . 13
7.7. Session Lifetime Option . . . . . . . . . . . . . . . . . 13
8. Processing Rules . . . . . . . . . . . . . . . . . . . . . . . 13
8.1. Authentication Data Generation . . . . . . . . . . . . . . 13
8.2. Authentication Data Validation . . . . . . . . . . . . . . 14
8.3. Sequence Number . . . . . . . . . . . . . . . . . . . . . 14
8.4. Retransmission Policies . . . . . . . . . . . . . . . . . 15
8.5. MTU Considerations . . . . . . . . . . . . . . . . . . . . 16
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
10. Security Considerations . . . . . . . . . . . . . . . . . . . 16
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 17
12. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . . 17
12.1. Changes from wasserman-pcp-authentication-02 to
ietf-pcp-authentication-00 . . . . . . . . . . . . . . . . 17
12.2. Changes from wasserman-pcp-authentication-01 to -02 . . . 17
12.3. Changes from wasserman-pcp-authentication-00 to -01 . . . 18
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18
13.1. Normative References . . . . . . . . . . . . . . . . . . . 18
13.2. Informative References . . . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19
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1. Introduction
Using the Port Control Protocol (PCP) [I-D.ietf-pcp-base], an IPv4 or
IPv6 host can flexibly manage the IP address mapping information on
its network address translators (NATs) and firewalls, and control
their policies in processing incoming and outgoing IP packets.
Because NATs and firewalls both play important roles in network
security architectures, there are many situations in which
authentication and access control are required to prevent un-
authorized users from accessing such devices. This document proposes
a PCP security extension which enables PCP servers to authenticate
their clients with Extensible Authentication Protocol (EAP). The
following issues are considered in the design of this extension:
o Loss of EAP messages during transportation
o Disordered delivery of EAP messages
o Generation of transport keys
o Integrity protection and data origin authentication for PCP
messages
o Algorithm agility
The mechanism described in this document meets the security
requirements to address the Advanced Threat Model described in the
base PCP specification [I-D.ietf-pcp-base]. This mechanism can be
used to secure PCP in the following situations::
o On security infrastructure equipment, such as corporate firewalls,
that does not create implicit mappings.
o On equipment (such as CGNs or service provider firewalls) that
serve multiple administrative domains and do not have a mechanism
to securely partition traffic from those domains.
o For any implementation that wants to be more permissive in
authorizing explicit mappings than it is in authorizing implicit
mappings.
o For implementations that support the THIRD_PARTY Option (unless
they can meet the constraints outlined in Section 14.1.2.2).
o For implementations that wish to support any deployment scenario
that does not meet the constraints described in Section 14.1.
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2. Terminology
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 RFC 2119 [RFC2119].
Most of the terms used in this document are introduced in
[I-D.ietf-pcp-base].
PCP Client: A PCP device (e.g., a host) which is responsible for
issuing PCP requests to a PCP server. In this document, a PCP client
is also a EAP peer [RFC3748], and it is the responsibility of a PCP
client to provide the credentials when authentication is required.
PCP Server: A PCP device (e.g., a NAT or a firewall) that implements
the server-side of the PCP protocol, via which PCP clients request
and manage explicit mappings. In this document, a PCP server is
integrated with an EAP authenticator [RFC3748]. Therefore, when
necessary, a PCP server can verify the credentials provided by a PCP
client and make an access control decision based on the
authentication result.
PCP Authentication (PCP Auth) Session: A series of PCP message
exchanges transferred between a PCP client and a PCP server in order
to perform authentication, authorization, key distribution and
secured PCP communication. Each PCP Auth session is assigned a
distinctive Session ID. The PCP devices involved within a PCP Auth
session are called session partners. A PCP Auth session has two
session partners.
Session Lifetime: The life period associated with a PCP Auth session,
which decided the lifetime of the current authorization given to the
PCP client.
PCP Security Association (PCP SA): A PCP security association is
formed between a PCP client and a PCP server by sharing cryptographic
keying material and associated context. The formed duplex security
association is used to protect the bidirectional PCP signaling
traffic between the PCP client and PCP server.
Master Session Key (MSK): A key derived by the partners of a PCP Auth
session, using an EAP key generating method (e.g., the one defined in
[RFC5448]).
PCP Auth (PCP Authentication) message: A PCP message containing an
Authentication OpCode for EAP authentication.
non PCP Auth message: A PCP message which is not a PCP Auth message.
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3. Separate vs. Inline Key Management
There is an open question in the working group regarding what
approach should be used for PCP key management. The precursor to
this document originally proposed an inline key management approach
using EAP directly over PCP. There was an alternative proposal on
the list to standardize a separate key management approach using PANA
[RFC5191] (with EAP). The WG will need to make a decision between
these two approaches before this document can be completed.
Both approaches for key management could be used with the integrity
protection mechanism and options described later in this document.
4. Separate Key Management
The separate key management proposal involves running PANA between
the end-points to dynamically generate a security association, and
then using that security association to authenticate PCP message
exchanges.
In pricinpal, the PANA message can be transported either through the
PCP port or through an different port. The latter option has been
abandoned by the working group since it may impose unnecessary
management burdens and cause issues in securely binding the PCP
session to the PANA session initiation.
The first option can be further broken down into two apporaches: The
PANA over PCP solution and the demultiplexing solution. For the
first approach [I-D.ohba-pcp-pana-encap], we would define an AVP for
PANA to indicate that the PANA session was being used for PCP
authentication, not for network access purposes. For the second
approach, we just re-use the PCP port to transport PANA message
[I-D.ohba-pcp-pana].
The first approach introduces little change on PANA. Howerer, there
are criticisms about the existence of overlapping fields on the PANA
and PCP headers that need to be check for consistency.
Compared with the first approach, the second approach does not have
this problem. However, addition work needs to be done to help an PCP
implementation to distinguish a PANA message from a PCP message.
There are some functions of PANA which are not necessary for PCP.
For example, it would not be necessary for these servers to support
IP Address Reconfiguration and re-authentication. It may be possible
to address this problem by defining a subset of the PANA protocol
that can be run on PCP Servers if the same PANA server will not be
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used for network access.
Once a secure session has been established using PANA, the Secure
OpCode option described in this draft could be used to associate PCP
requests with a particular PANA session.
Although a separate key management approach using PANA has been
discussed on the PCP mailing list, this approach would require
further documentation if the WG decides to pursue it.
5. Protocol Details
5.1. Session Initiation
To carry out an EAP authentication process between two PCP devices, a
set of PCP Auth messages need to be exchanged. A PCP Auth message
contains an Authentication OpCode and associated Options. The
Authentication OpCode consists of three fields: Session ID, Flag, and
Sequence Number. The Session ID field is used to identify the
session to which the message belongs. The Flag field indicates the
type of the PCP message. The sequence number field is used to detect
the disorder or the duplication occurred during packet delivery.
The message exchanges conveyed within an PCP Auth session is
introduced in the remainder section.
When a PCP client intends to initiate a PCP Auth session with a PCP
server, it sends a PCC-Initiation message to the PCP server. In the
message, the Session ID and Sequence Number fields of the
Authentication OpCode are set as 0; the I bit is set. The PCC-
Initiation message is also attached with a nonce option which
consists of a random nonce selected by the PCP client. The nonce
will be used by the PCP client to check the freshness of the initial
message from the PCP server. After receiving the PCC-Initiation, if
the PCP server would like to initiate a PCP Auth session, it will
reply with a PCP-Auth-Request which contains an EAP Identity Request.
The Sequence Number field in the PCP-Auth-Request is set as 0, and
the Session ID field MUST be filled with the session identifier
assigned by the PCP server for this session. The PCP-Auth-Request
needs to be attached with a nonce option which is learned from the
PCP client. From now on, every PCP Auth message within this session
must be attached with the session identifier. When receiving a PCP
Auth message from an unknown session, a PCP device MUST discard the
message silently. If the PCP client intends to simplify the
authentication process, it can append an EAP Identity Response
message within the PCC-Initiation request so as to inform the PCP
server that it would like to perform EAP authentication and skip the
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step of waiting for the EAP Identity Request.
In the scenario where a PCP server receives a non-PA PCP message from
a PCP client which needs to be authenticated, the PCP server can
reply with a PCP-Auth-Request to initiate a PCP Auth session; the
result code field of the PCP-Auth-Request is set as AUTHENTICATION-
REQUIRED. In addition, the PCP server MUST assign a session ID for
the session and transfer it within the PCP-Auth-Request. In the PCP
Auth messages exchanged afterwards in this session, the session ID
MUST be appended. Therefore, in the subsequent communication, the
PCP client can distinguish the messages in this session from those in
other sessions through the PCP server IP address and the session ID.
When the PCP client receives the initial PCP-Auth-Request message
from the PCP server, it can reply with a PCP-Auth-Answer message to
continue the session or silently discard the request message
according to its local policies.
In a PCP Auth session, PCP-Auth-Request messages are sent from PCP
servers to PCP clients while PCP-Auth-Answer messages are only sent
from PCP clients to PCP servers. Correspondently, an EAP request
message MUST be transported within a PCP-Auth-Request message, and an
EAP answer message MUST be transported within a PCP-Auth-Answer
message. Particularly, when a PCP device receives a PCP-Auth-Request
or a PCP-Auth-Answer message from its partner, the PCP device needs
to reply with a PCP-Auth-Acknowledge message to indicate that the
message has been received. This solution is used to deal with the
conditions where the device cannot generate a response within a pre-
specified period due to certain reasons (e.g., waiting for human
input to construct a EAP message). Therefore, the partner does not
have to un-necessarily retransmit the PCP message.
In this approach, it is mandated for a PCP client and a PCP server to
perform a key-generating EAP method in authentication. Therefore,
after a successful authentication procedure, a Master Session Key
(MSK) will be generated. If the PCP client and the PCP server want
to generate a traffic key using the MSK, they need to agree upon a
Pseudo-Random Function (PRF) for the transport key derivation and a
MAC algorithm to provide data origin authentication for subsequent
PCP packets. On this occasion, the PCP server needs to append the
initial PCP-Auth-Request message with a set of PRF Options and MAC
Algorithm Options. Each PRF Option contains a PRF that the PCP
server supports. Similarly, each MAC Algorithm Option contains a MAC
(Message Authentication Code) algorithm that the PCP server supports.
After receiving the request, the PCP client selects a PRF and a MAC
algorithm which it would like to use, and sends back a PCP-Auth-
Answer with a PRF Option and a MAC Algorithm Option for the selected
algorithm.
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The last PCP-Auth-Request message transported within a PCP Auth
session carries the EAP authentication and PCP authorization results.
The last PCP-Auth-Request and PCP-Auth-Answer messages MUST have the
'C' (Complete) bit set.
If the EAP authentication succeeds, the result code of the last PCP-
Auth-Request is AUTHENTICATION-SUCCESS. In this case, before sending
out the PCP-Auth-Request, the PCP server must derive a transport key
and use it to generate digests to protect the integrity and
authenticity of the PCP-Auth-Request and any subsequent PCP message.
Such digests are transported within Authentication Tag Options. In
addition, the PCP-Auth-Request needs to be appended with a Session
Lifetime Option which indicates the life-time of the PCP Auth session
(i.e., the life-time of the MSK).
If the EAP authentication fails, the result code of the last PCP-
Auth-Request is AUTHENTICATION-FAILED. If the EAP authentication
succeeds but Authorization fails, the result code of the last PCP-
Auth-Request is AUTHORIZATION-FAILED. In the latter two cases, the
PCP Auth session MUST be terminated immediately after the last PCP
authentication message exchange.
5.2. Session Termination
A PCP Auth session can be explicitly terminated by sending a
termination-indicating PCP Auth acknowledge message from either
session partner. After receiving a termination-indicating message
from the session partner, a PCP device MUST respond with a
termination-indicating PCP Auth Acknowledge message and remove the
PCP Auth SA immediately. When the session partner initiating the
termination process receives the acknowledge message, it will remove
the associated PCP Auth SA immediately.
6. PA Security Association
At the beginning of a PCP Auth session, a session SHOULD generate a
PCP Auth SA to maintain its state information during the session.
The parameters of a PCP Auth SA are listed as follows:
o IP address and UDP port number of the PCP client
o IP address and UDP port number of the PCP server
o Session Identifier
o Sequence number for the next outgoing PCP message
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o Sequence number for the next incoming PCP message
o Last outgoing message payload
o Retransmission interval
o MSK
o MAC algorithm: The algorithm that the transport key should use to
generate digests for PCP messages.
o Pseudo-random function: The pseudo random function negotiated in
the initial PCP-Auth-Request and PCP-Auth-Answer exchange for the
transport key derivation
o Transport key: the key derived from the MSK to provide integrity
protection and data origin authentication for the messages in the
PCP Auth session. The life-time of the transport key SHOULD be
identical to the life-time of the session.
Particularly, the transport key is computed in the following way:
Transport key = prf(MSK, "IETF PCP"| Session_ID, key ID), where:
o The prf: The pseudo-random function assigned in the Pseudo-random
function parameter.
o MSK: The master session key generated by the EAP method.
o "IETF PCP": The ASCII code representation of the non-NULL
terminated string (excluding the double quotes around it).
o Session_ID: The ID of the session which the MSK is derived from
o Key ID: The ID assigned for the traffic key
7. Packet Format
7.1. Authentication OpCode Format
The following figure illustrates the format of an authentication
Opcode:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|I C R K T S E| Reserved | Result Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Session ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Flags: The Flags field is two octets. The following bits are
assigned:
I (Initiation): This bit is set in a PCC-Initiation message.
C (Complete): If the message is the last PCP-Auth-Request or PCP-
Auth-Answer message in the session, this bit MUST be set. For
other messages, this bit MUST be cleared.
R (Request): This bit is set in a PCP-Auth-Request message, and
un-set in a PCP-Auth-Answer message.
K (acKnowledgement): This bit is set and only set in a PCP-Auth-
Acknowledgement message.
T (Termination): If this bit is set in a PCP-Auth-Acknowledgement
message, the message is used for session-termination indication.
Session ID: This field contains a 32-bit PCP Auth session
identifier.
Sequence Number: This field contains a 32-bit sequence number. In
this solution, a sequence number needs to be incremented on every
new (non-retransmission) outgoing packet in order to provide
ordering guarantee for PCP.
Result Code: This field is two octets. The following values are
defined:
1 AUTHENTICATION-REQUIRED
2 AUTHENTICATION-FAILED
3 AUTHENTICATION-SUCCESS
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4 AUTHORIZATION-FAILED
7.2. Nonce Option
Because the session identifier of PCP Auth session is determined by
the PCP server, a PCP client does not know the session identifier
which will be used when it sends out a PCC-Initiation message. In
order to prevent an attacker from interrupting the authentication
process by sending off-line generated PCP-Auth-Request messages, the
PCP client needs to generate a random number as nonce in the PCC-
Initiation message. The PCP server will append the nonce within the
initial PCP-Auth-Request message. If the PCP-Auth-Request message
does not carry the correct nonce, the message will be discarded
silently.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Code | Reserved | Option-Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Nonce |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Nonce: A random 32 bits number which is transported within a PCC-
Initiate message and the corresponding reply message from the PCP
server.
7.3. Authentication Tag Option
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Code | Reserved | Option-Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Session ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Key ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Authentication Data (Variable) |
~ ~
| |
| |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Option-Length: The length of the Authentication Tag Option (in
octet), including the 8 octet fixed header and the variable length
of the authentication data.
Session ID: A 32-bit field used to indicates the identifier of the
session that the message belongs to and identifies the secret key
used to create the message digest appended to the PCP message.
Key ID: The ID associated with the traffic key used to generate
authentication data. This field is filled with zero if MSK is
directly used to secure the message.
Authentication Data: A variable-length field that carries the
Message Authentication Code for the PCP packet. The generation of
the digest can be various according to the algorithms specified in
different PCP SAs. This field MUST end on a 32-bit boundary,
padded with 0's when necessary.
7.4. EAP Payload Option
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Code | Reserved | Option-Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| EAP Message |
~ ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
EAP Message: The EAP message transferred. Note this field MUST
end on a 32-bit boundary, padded with 0's when necessary.
7.5. PRF Option
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Code | Reserved | Option-Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PRF |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
PRF: The Pseudo-Random Function which the sender supports to
generate an MSK. This field contains an IKEv2 Transform ID of
Transform Type 2 [RFC4306].
7.6. Hash Algorithm Option
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Code | Reserved | Option-Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAC Algorithm ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
MAC Algorithm ID: Indicate the MAC algorithm which the sender
supports to generate authentication data. The MAC Algorithm ID field
contains an IKEv2 Transform ID of Transform Type 3 [RFC4306].
7.7. Session Lifetime Option
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Code | Reserved | Option-Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Session Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Session Lifetime: The life time of the PCP Auth Session, which is
decided by the authorization result.
8. Processing Rules
8.1. Authentication Data Generation
If a PCP SA is generated as the result of a successful EAP
authentication process, every subsequent PCP message within the
session MUST carry an Authentication Tag Option which contains the
digest of the PCP message for data origin authentication and
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integrity protection.
Before generating a digest for a PCP message, a device needs to first
select a traffic key in the session and append the Authentication Tag
Option at the end of the protected PCP message. The length of the
Authentication Data field is decided by the MAC algorithm adopted in
the session. The device then fills the Session ID field and the PCP
SA ID field, and sets the Authentication Data field to 0. After
this, the device generates a digest for the entire PCP message
(including the PCP header and Authentication Tag Option) with the MAC
algorithm and the selected traffic key, and input the generated
digest into the Authentication Data field.
8.2. Authentication Data Validation
When a device receives a PCP packet with an Authentication Tag
Option, it needs to use the session ID transported in the option to
locate the proper SA, and then find the associated transport key
(using key ID) and the MAC algorithm. If no proper SA is found, the
PCP packet MUST be discarded silently. After storing the value of
the Authentication field of the Authentication Tag Option, the device
fills the Authentication field with zeros. Then, the device
generates a digest for the packet (including the PCP header and
Authentication Tag Option) with the transport key and the MAC
algorithm found in the first step. If the value of the newly
generated digest is identical to the stored one, the device can
ensure that the packet has not been tampered with, and the validation
succeeds. Otherwise, the packet MUST be discarded.
8.3. Sequence Number
PCP adopts UDP to transport signaling messages. As an un-reliable
transport protocol, UDP does not guarantee ordered packet delivery
and does not provide any protection from packet loss. In order to
ensure the EAP messages are exchanged in a reliable way, every PCP
packet exchanged during EAP authentication must carry an
monotonically increasing sequence number. During a PCP Auth session,
a PCP device needs to maintain two sequence numbers, one for incoming
packets and one for outgoing packets. When generating an outgoing
PCP packet, the device attaches the outgoing sequence number to the
packet and increments the sequence number maintained in the SA by 1.
When receiving a PCP packet from its session partner, the device will
not accept it if the sequence number carried in the packet does not
match the incoming sequence number the device maintains.
After confirming that the received packet is valid, the device
increments the incoming sequence number maintained in the SA by 1.
However, the above rules are not applied to PCP-Auth-Acknowledgement
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messages. When receiving or sending out a PCP-Auth-Acknowledgement
message, the device does not increase the corresponding sequence
number stored in the SA. Another exception is message
retransmission. When a device does not receive any response message
from its session partner in a certain period, it needs to retransmit
the last sent message with a limited rate. The duplicate messages
and the original message MUST use the identical sequence number.
When the device receives such duplicate messages from its session
partner, it MUST try to answer them by sending the last outgoing
message with a limited rate unless it has received another valid
message with a larger sequence number from its session. In such
cases, the maintained incoming and outgoing sequence numbers will not
be affected by the message retransmission.
8.4. Retransmission Policies
This work provides a retransmission mechanism for reliable PCP Auth
message delivery. The timer, the variables, and the rules used in
this mechanism are adopted from PANA.
The retransmission behavior is controlled and described by the
following variables:
RT: Retransmission timeout from the previous (re)transmission
IRT: Base value for RT for the initial retransmission
MRC: Maximum retransmission count
MRT: Maximum retransmitting time interval
RAND: Randomization factor
With each message transmission or retransmission, the sender sets RT
according to the rules given below.
If RT expires before receiving any reply, the sender re-calculates RT
and retransmits the message. Each of the computations of a new RT
includes a randomization factor (RAND), which is a random number
chosen with a uniform distribution between -0.1 and +0.1. The
randomization factor is included to minimize the synchronization of
messages. The algorithm for choosing a random number does not need
to be cryptographically sound. The algorithm SHOULD produce a
different sequence of random numbers from each invocation. RT for
the first message retransmission is based on IRT:
RT = IRT
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RT for each subsequent message retransmission is based on the
previous value of RT (RTprev):
RT = (2+RAND) * RTprev
MRT specifies an upper bound on the value of RT (disregarding the
randomization added by the use of RAND). If MRT has a value of 0,
there is no upper limit on the value of RT. Otherwise:
if (RT > MRT)
RT = (1+RAND) * MRT
MRC specifies an upper bound on the number of times a sender may
retransmit a message. Unless MRC is zero, the message exchange fails
once the sender has transmitted the message MRC times. In this case,
the sender needs to start a session termination process illustrated
in Section 3.2.
8.5. MTU Considerations
EAP methods are responsible for MTU handling, so no special
facilities are required in this protocol to deal with MTU issues.
9. IANA Considerations
TBD
10. Security Considerations
This section applies only to the in-band key management mechanism.
It will need to be updated if the WG choose to pursue the out-of-band
key management mechanism discussed above.
In this work, after a successful EAP authentication process performed
between two PCP devices, a MSK will be exported. The MSK can be used
to derive the transport keys to generate MAC digests for subsequent
PCP message exchanges. This work does not exclude the possibility of
using the MSK to generate keys for different security protocols to
enable per-packet cryptographic protection. The methods of deriving
the transport key for the security protocols is out of scope of this
document.
However, before a transport key has been generated, the PCP Auth
messages exchanged within a PCP Auth session have little
cryptographic protection, and if there is no already established
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security channel between two session partners, these messages are
subject to man-in-the-middle attacks and DOS attacks. For instance,
the initial PCP-Auth-Request and PCP-Auth-Answer exchange is
vulnerable to spoofing attacks as these messages are not
authenticated and integrity protected. In order to prevent very
basic DOS attacks, a PCP device SHOULD generate state information as
little as possible in the initial PCP-Auth-Request and PCP-Auth-
Answer exchanges. The choice of EAP method is also very important.
The selected EAP method must be resilient to the attacks possibly in
an insecure network environment, and the user-identity
confidentiality, protection against dictionary attacks, and session-
key establishment must be supported.
11. Acknowledgements
12. Change Log
12.1. Changes from wasserman-pcp-authentication-02 to ietf-pcp-
authentication-00
o Added discussion of in-band and out-of-band key management
options, leaving choice open for later WG decision.
o Removed support for fragmenting EAP messages, as that is handled
by EAP methods.
12.2. Changes from wasserman-pcp-authentication-01 to -02
o Add a nonce into the first two exchanged PCP Auth message between
the PCP client and PCP server. When a PCP client initiate the
session, it can use the nonce to detect offline attacks.
o Add the key ID field into the authentication tag option so that a
MSK can generate multiple traffic keys.
o Specify that when a PCP device receives a PCP-Auth-Request or a
PCP-Auth-Answer message from its partner the PCP device needs to
reply with a PCP-Auth-Acknowledge message to indicate that the
message has been received.
o Add the support of fragmenting EAP messages.
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12.3. Changes from wasserman-pcp-authentication-00 to -01
o Editorial changes, added use cases to introduction.
13. References
13.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
13.2. Informative References
[I-D.ietf-pcp-base]
Wing, D., Cheshire, S., Boucadair, M., Penno, R., and P.
Selkirk, "Port Control Protocol (PCP)",
draft-ietf-pcp-base-28 (work in progress), October 2012.
[I-D.ohba-pcp-pana]
Ohba, Y., Tanaka, Y., Das, S., Yegin, A., and T. Tsou,
"Provisioning Message Authentication Key for PCP using
PANA (Side-by-Side Approach)", draft-ohba-pcp-pana-03
(work in progress), October 2012.
[I-D.ohba-pcp-pana-encap]
Ohba, Y., Yegin, A., and S. Das, "Provisioning Message
Authentication Key for PCP using PANA (Encapsulation
Approach)", draft-ohba-pcp-pana-encap-00 (work in
progress), October 2012.
[RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H.
Levkowetz, "Extensible Authentication Protocol (EAP)",
RFC 3748, June 2004.
[RFC4306] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol",
RFC 4306, December 2005.
[RFC5191] Forsberg, D., Ohba, Y., Patil, B., Tschofenig, H., and A.
Yegin, "Protocol for Carrying Authentication for Network
Access (PANA)", RFC 5191, May 2008.
[RFC5448] Arkko, J., Lehtovirta, V., and P. Eronen, "Improved
Extensible Authentication Protocol Method for 3rd
Generation Authentication and Key Agreement (EAP-AKA')",
RFC 5448, May 2009.
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Authors' Addresses
Margaret Wasserman
Painless Security
356 Abbott Street
North Andover, MA 01845
USA
Phone: +1 781 405 7464
Email: mrw@painless-security.com
URI: http://www.painless-security.com
Sam Hartman
Painless Security
356 Abbott Street
North Andover, MA 01845
USA
Email: hartmans@painless-security.com
URI: http://www.painless-security.com
Dacheng Zhang
Huawei
Beijing,
China
Phone:
Fax:
Email: zhangdacheng@huawei.com
URI:
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