One document matched: draft-ietf-dhc-sedhcpv6-10.xml
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<rfc category="std" docName="draft-ietf-dhc-sedhcpv6-10" ipr="trust200902">
<front>
<title abbrev="SeDHCPv6">Secure DHCPv6</title>
<author fullname="Sheng Jiang" initials="S." surname="Jiang">
<organization>Huawei Technologies Co., Ltd</organization>
<address>
<postal>
<street>Q14, Huawei Campus, No.156 Beiqing Road</street>
<city>Hai-Dian District, Beijing, 100095</city>
<country>CN</country>
</postal>
<email>jiangsheng@huawei.com</email>
</address>
</author>
<author fullname="Lishan Li" initials="L." surname="Li">
<organization>Tsinghua University</organization>
<address>
<postal>
<street></street>
<city>Beijing</city>
<code>100084</code>
<country>P.R.China</country>
</postal>
<phone>+86-15201441862</phone>
<email>lilishan9248@126.com</email>
</address>
</author>
<author fullname="Yong Cui" initials="Y." surname="Cui">
<organization>Tsinghua University</organization>
<address>
<postal>
<street></street>
<city>Beijing</city>
<code>100084</code>
<country>P.R.China</country>
</postal>
<phone>+86-10-6260-3059</phone>
<email>yong@csnet1.cs.tsinghua.edu.cn</email>
</address>
</author>
<author fullname="Tatuya Jinmei" initials="T." surname="Jinmei">
<organization>Infoblox Inc.</organization>
<address>
<postal>
<street>3111 Coronado Drive</street>
<city>Santa Clara</city>
<region>CA</region>
<country>US</country>
</postal>
<email>jinmei@wide.ad.jp</email>
</address>
</author>
<author fullname="Ted Lemon" initials="T." surname="Lemon">
<organization>Nominum, Inc.</organization>
<address>
<postal>
<street>2000 Seaport Blvd</street>
<city>Redwood City, CA</city>
<code>94063</code>
<country>USA</country>
</postal>
<phone>+1-650-381-6000</phone>
<email>Ted.Lemon@nominum.com</email>
</address>
</author>
<author fullname="Dacheng Zhang" initials="D." surname="Zhang">
<address>
<postal>
<street></street>
<city>Beijing</city>
<country>CN</country>
</postal>
<email>dacheng.zhang@gmail.com</email>
</address>
</author>
<date month="" year="2015" />
<area>Internet Area</area>
<workgroup>DHC Working Group</workgroup>
<keyword>Secure</keyword>
<keyword>DHCPv6</keyword>
<keyword>Public Key</keyword>
<abstract>
<t>The Dynamic Host Configuration Protocol for IPv6 (DHCPv6) enables
DHCPv6 servers to pass configuration parameters. It offers configuration
flexibility. If not being secured, DHCPv6 is vulnerable to various
attacks. This document analyzes the security issues of DHCPv6 and
specifies a secure DHCPv6 mechanism for the authentication and
encryption between DHCPv6 client and DHCPv6 server.</t>
</abstract>
</front>
<middle>
<section title="Introduction">
<t>The Dynamic Host Configuration Protocol for IPv6 (DHCPv6, <xref
target="RFC3315"></xref>) enables DHCPv6 servers to pass configuration
parameters and offers configuration flexibility. If not being secured,
DHCPv6 is vulnerable to various attacks.</t>
<t>This document analyzes the security issues of DHCPv6 in details and
provides the following mechanisms for improving the security of DHCPv6
between client and server:<list style="symbols">
<t>the authentication of the DHCPv6 client and the DHCPv6 server to
defend against active attack, such as spoofing attack.</t>
<t>the encryption between the DHCPv6 client and the DHCPv6 server in
order to protect the DHCPv6 from passive attack, such as pervasive
monitoring.</t>
<t>the integrity check of DHCPv6 messages by the recipient of the
message based on signature.</t>
<t>anti-replay protection based on timestamps.</t>
</list></t>
<t>Note: this secure mechanism in this document does not protect outer
options in Relay-Forward and Relay-Reply messages, either added by a
relay agent toward a server or added by a server toward a relay agent,
because they are only transported within operator networks and
considered less vulnerable. Communication between a server and a relay
agent, and communications between relay agents, may be secured through
the use of IPsec, as described in section 21.1 in <xref
target="RFC3315"></xref>.</t>
<t>The security mechanisms specified in this document achieves the
DHCPv6 authentication and encryption based on the sender's public key
certificate. We introduce two new DHCPv6 messages: Encrypted-Query
message and Encrypted-Response message and four new DHCPv6 options:
certificate option, signature option, timestamp option and
encrypted-message option for the DHCPv6 authentication and encryption.
The certificate option is used for the DHCPv6 authentication. It also
integrates signature option for the integrity check and timestamps
option for anti-replay protection. The Encryption-Query message,
Encryption-Response message, and encrypted-message option are used for
the DHCPv6 encryption.</t>
<!--
<t>The security mechanism specified in this document is based on DHCPv6
client/server's certificates with associated private keys. It also
integrates message signatures for the integrity
and timestamps for anti-replay. The sender authentication procedure
using certificates defined in this document depends on deployed Public
Key Infrastructure (PKI, <xref target="RFC5280"></xref>). However, the
deployment of PKI is out of the scope of this document.</t>
-->
</section>
<section title="Requirements Language and 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"></xref> when they appear in ALL CAPS. When these words
are not in ALL CAPS (such as "should" or "Should"), they have their
usual English meanings, and are not to be interpreted as <xref
target="RFC2119"></xref> key words.</t>
</section>
<section title="Terminology">
<t>This section defines terminology specific to secure DHCPv6 used in
this document.</t>
<t><list hangIndent="16" style="hanging">
<t hangText="secure DHCPv6 client:">A node that initiates the DHCPv6
request on a link to obtain the DHCPv6 configuration parameters from
one or more DHCPv6 servers. The configuration process is
authenticated and encrypted using the defined mechanisms in this
document.</t>
<t hangText="secure DHCPv6 server:">A node that responds to requests
from clients using the authentication and encryption mechanism
defined in this document.</t>
</list></t>
</section>
<section title="Security Issues of DHCPv6">
<t>DHCPv6 is a client/server protocol that provides managed
configuration of devices. It enables a DHCPv6 server to automatically
configure relevant network parameters on clients. The basic DHCPv6
specification <xref target="RFC3315"></xref> defines security
mechanisms, but they have significant flaws and can be improved</t>
<t>The basic DHCPv6 specifications can optionally authenticate the
origin of message and validate the integrity of messages using an
authentication option with a symmetric key pair. <xref
target="RFC3315"></xref> relies on pre-established secret keys. For any
kind of meaningful security, each DHCPv6 client would need to be
configured with its own secret key; <xref target="RFC3315"></xref>
provides no mechanism for doing this.</t>
<!--
<t>For the keyed hash function, there are two key management mechanisms.
The first one is a key management done out of band, usually through some
manual process. The second approach is to use Public Key Infrastructure
(PKI).</t>
-->
<t>For the out of band approach, operators can set up a key database for
both servers and clients from which the client obtains a key before
running DHCPv6. Manual key distribution runs counter to the goal of
minimizing the configuration data needed at each host.</t>
<t><xref target="RFC3315"></xref> provides an additional mechanism for
preventing off-network timing attacks using the Reconfigure message: the
Reconfigure Key authentication method. However, this method provides
little message integrity or source integrity check, and it protects only
the Reconfigure message. This key is transmitted in plaintext.</t>
<t>In addition, the current DHCPv6 messages are still transmitted in
clear text and the privacy information within the DHCPv6 message is not
protected from passive attack, such as pervasive monitoring. The IETF
has expressed strong agreement that PM is an attack that needs to be
mitigated where possible in <xref target="RFC7258"></xref>.</t>
<t>In comparison, the security mechanism defined in this document
provides the authentication and encryption mechanism based on the public
key certificates on the client or server. The DHCPv6 authentication can
protect DHCPv6 from active attack, such as spoofing attack. And the
DHCPv6 encryption defends against passive attack, such as pervasive
monitoring attack.</t>
</section>
<section title="secure DHCPv6 overview">
<section title="Solution Overview">
<t>This solution provides the authentication and encryption mechanisms
based on the public certificates of the DHCPv6 client and server.
Before the standard DHCPv6 configuration process, the
Information-request and Reply messages are exchanged to select one
authenticated DHCPv6 server. The following DHCPv6 configuration
process is encrypted to avoid the privacy disclosure. We introduce two
new DHCPv6 messages: Encrypted-Query message, Encrypted-Response
message and four new DHCPv6 options: encrypted-message option,
certificate option, signature option, timestamp option. Based on the
new defined messages and options, the corresponding authentication and
encryption mechanisms are proposed.</t>
<t>The following figure illustrates the secure DHCPv6 procedure. The
DHCPv6 client first sends an Information-request message to the
standard multicast address to all DHCPv6 servers. The
Information-request message is used to request the servers for server
authentication information, without going through any address, prefix
or non-security option assignment process. The information-request is
sent without client's privacy information, such as client identifier
option to minimize information leak and increase client's privacy.
When receiving the Information-request message, the server sends the
Reply message that contains the server's certificate option, signature
option, timestamp option, and server identifier option. Upon the
receipt of the Reply message, the DHCPv6 client verifies the server's
identity according to the contained server authentication information
in Reply message. If there are multiple authenticated DHCPv6 servers,
the client selects one authenticated DHCPv6 server for the following
DHCPv6 configuration process. If there are no authenticated DHCPv6
servers or existing servers failed authentication, the client behavior
is policy specific. Depending on its policy, it can choose to connect
repeat the server discovery process after certain delay or attempt to
connect to a different network.</t>
<t>After the server's authentication, the first DHCPv6 message sent
from client to server, such as Solicit message, contains the client's
certificate option, signature option and timestamp option for client
authentication. The DHCPv6 message sent from client to server is
encrypted with the server's public key and encapsulated into the
encrypted-message option. The DHCPv6 client sends the Encrypted-Query
message to server, which carries the server identifier option and the
encrypted-message option. When the DHCPv6 server receives the
Encrypted-Query message, it decrypts the message using its private
key. If the decrypted message contains the client's certificate
option, signature option, timestamp option, the DHCPv6 server verifies
the client's identity according to the contained client authentication
information. After the client's authentication, the server sends the
Encrypted-Response message to the client, which contains the
encrypted-message option. The encrypted-message option contains the
encrypted DHCPv6 message sent from server to client, which is
encrypted using the client's public key. The message that fails client
authentication, MUST be dropped. And the server sends the
corresponding error status code to client.</t>
<figure align="center" title="Secure DHCPv6 Procedure">
<artwork><![CDATA[
+-------------+ +-------------+
|DHCPv6 Client| |DHCPv6 Server|
+-------------+ +-------------+
| Information-request |
|----------------------------------------->|
| Option Request option |
| |
| Reply |
|<-----------------------------------------|
| certificate option |
| signature option |
| timestamp option |
| server identifier option |
| |
| Encryption-Query |
|----------------------------------------->|
| encrypted-message option |
| server identifier option |
| |
| Encryption-Response |
|<-----------------------------------------|
| encrypted-message option |
| |
]]></artwork>
</figure>
<t>It is worth noticing that the signature on a Secure DHCPv6 message
can be expected to significantly increase the size of the message. One
example is normal DHCPv6 message length plus a 1 KB for a X.509
certificate and signature and 256 Byte for a signature. IPv6 fragments
<xref target="RFC2460"></xref> are highly possible. In practise, the
total length would be various in a large range. Hence, deployment of
Secure DHCPv6 should also consider the issues of IP fragment, PMTU,
etc. Also, if there are firewalls between secure DHCPv6 clients and
secure DHCPv6 servers, it is RECOMMENDED that the firewalls are
configured to pass ICMP Packet Too Big messages <xref
target="RFC4443"></xref>.</t>
</section>
<section title="New Components">
<t>The new components of the solution specified in this document are
as follows:</t>
<t><list style="symbols">
<t>Servers and clients that use certificates first generate a
public/private key pair and then obtain a public key certificate
from a Certificate Authority that signs the public key. One option
is defined to carry the certificate.</t>
<t>A signature generated using the private key which is used by
the receiver to verify the integrity of the DHCPv6 messages and
then the authentication of the client/server. Another option is
defined to carry the signature.</t>
<t>A timestamp that can be used to detect replayed packet. The
secure DHCPv6 client/server need to meet some accuracy
requirements and be synced to global time, while the timestamp
checking mechanism allows a configurable time value for clock
drift. The real time provision is out of scope of this document.
Another option is defined to carry the current time of the
client/server.</t>
<t>An encrypted-message option that contains the encrypted DHCPv6
message.</t>
<t>An Encrypted-Query message that sent from client to server. The
Encrypted-Query message contains the encrypted-message option and
server identifier option.</t>
<t>An Encrypted-Response message that sent from server to client.
The Encrypted-Response message contains the encrypted-message
option.</t>
</list></t>
</section>
<section title="Support for Algorithm Agility">
<t>Hash functions are used to provide message integrity checks. In
order to provide a means of addressing problems that may emerge in the
future with existing hash algorithms, as recommended in <xref
target="RFC4270"></xref>, this document provides a mechanism for
negotiating the use of more secure hashes in the future.</t>
<t>In addition to hash algorithm agility, this document also provides
a mechanism for signature algorithm agility.</t>
<t>The support for algorithm agility in this document is mainly a
unilateral notification mechanism from sender to recipient. A
recipient MAY support various algorithms simultaneously among
different senders, and the different senders in the same
administrative domain may be allowed to use various algorithms
simultaneously. It is NOT RECOMMENDED that the same sender and
recipient use various algorithms in a single communication
session.</t>
<t>If the recipient does not support the algorithm used by the sender,
it cannot authenticate the message. In the client-to-server case, the
server SHOULD reply with an AlgorithmNotSupported status code (defined
in <xref target="StatusCodes"></xref>). Upon receiving this status
code, the client MAY resend the message protected with the mandatory
algorithm (defined in <xref target="SigOption"></xref>).</t>
</section>
<section title="Imposed Additional Constraints">
<t>The client/server that supports the identity verification MAY
impose additional constraints for the verification. For example, it
may impose limits on minimum and maximum key lengths.</t>
<t><list style="hanging">
<t hangText="Minbits">The minimum acceptable key length for public
keys. An upper limit MAY also be set for the amount of computation
needed when verifying packets that use these security
associations. The appropriate lengths SHOULD be set according to
the signature algorithm and also following prudent cryptographic
practice. For example, minimum length 1024 and upper limit 2048
may be used for RSA <xref target="RSA"></xref>.</t>
</list></t>
</section>
<section title="Applicability">
<t>Secure DHCPv6 is applicable in environments where physical security
on the link is not assured and attacks on DHCPv6 are a concern, such
as enterprise network. In enterprise network, the security policy is
strict and the clients are stable terminals. The PKI model is used for
the secure DHCPv6 deployment. The deployment of PKI is out of the
scope of this document. The server is always considered to have
connectivity to authorized CA and verify the clients' certificates.
The client performs the server authentication locally. The trusted
servers' certificates or trusted CAs' certificates, which form a
certification path <xref target="RFC5280"></xref>, is deployed in the
client to achieve the server authentication. The DHCPv6 client obtains
the trusted certificates through the pre-configuration method or out
of band, such as QR code. After the mutual authentication, the DHCPv6
message is encrypted with the recipient's public key, which is
contained in the certificate.</t>
</section>
</section>
<section title="DHCPv6 Client Behavior">
<t>For the security DHCPv6 client, it must have a public certificate.
The client may be pre-configured with a public key certificate, which is
signed by a CA trusted by the server, and its corresponding private
key.</t>
<t>The DHCPv6 client multicasts the Information-request message to the
DHCPv6 servers. The Information-request message MUST NOT include any
option which may reveal the private information of the client, such as
the client identifier option. The information-request message is used by
the DHCPv6 client to request the server's identity verification
information without having addresses, prefixes or any non-security
options assigned to it. The Option Request option in the
Information-request message MUST contain the option code of certificate
option, signature option, timestamp option, and server identifier
option.</t>
<t>When receiving the Reply messages from DHCPv6 servers, a secure
DHCPv6 client SHOULD discard any DHCPv6 messages that meet any of the
following conditions:<list style="symbols">
<t>the signature option is missing,</t>
<t>multiple signature options are present,</t>
<t>the certificate option is missing.</t>
</list></t>
<t>And then the client SHOULD first check the support of the hash and
signature algorithms that the server used. If the check fails, the Reply
message SHOULD be dropped. If both hash and signature algorithms are
supported, the client then checks the authority of this server. The
client SHOULD also use the same algorithms in the return messages.</t>
<t>The client SHOULD validate the certificate according to the rules
defined in <xref target="RFC5280"></xref>. An implementation may create
a local trust certificate record for verified certificates in order to
avoid repeated verification procedure in the future. A certificate that
finds a match in the local trust certificate list is treated as
verified. At this point, the client has either recognized the
authentication of the server, or decided to drop the message.</t>
<t>The client MUST now authenticate the server by verifying the
signature and checking timestamp (see details in <xref
target="timestampCheck"></xref>), if there is a timestamp option. The
order of two procedures is left as an implementation decision. It is
RECOMMENDED to check timestamp first, because signature verification is
much more computationally expensive.</t>
<t>The signature field verification MUST show that the signature has
been calculated as specified in <xref target="SigOption"></xref>. Only
the messages that get through both the signature verification and
timestamp check (if there is a timestamp option) are accepted. Reply
message that does not pass the above tests MUST be discarded.</t>
<t>If there are multiple authenticated DHCPv6 servers, the client
selects one DHCPv6 server for the following network parameters
configuration. If there are no authenticated DHCPv6 servers or existing
servers failed authentication, the client behavior is policy specific.
Depending on its policy, it can choose to connect using plain,
unencrypted DHCPv6, repeat the server discovery process after certain
delay or attempt to connect to a different network. The client MUST NOT
conduct the server discovery process immediately to avoid the packet
storm.</t>
<t>Once the server has been authenticated, the DHCPv6 client sends the
Encrypted-Query message to the DHCPv6 server. The Encrypted-Query
message is constructed with the encrypted-message option, which MUST be
constructed as explained in <xref target="EncryMesOption"></xref>, and
server identifier option. The encrypted-message option contains the
DHCPv6 message that is encrypted using the selected server's public key.
The server identifier option is externally visible to avoid extra of
decryption cost by those unselected servers.</t>
<t>The information for client authentication is contained in the
Solicit/Information-request message, which is encrypted and then
encapsulated into the Encrypted-Query message to avoid client privacy
disclosure. The Solicit/Information-request message MUST contain the
certificate option, which MUST be constructed as explained in <xref
target="CertOption"></xref>. In addition, one and only one signature
option MUST be contained, which MUST be constructed as explained in
<xref target="SigOption"></xref>. It protects the message header and all
DHCPv6 options except for the Authentication Option. One and only one
Timestamp option, which MUST be constructed as explained in <xref
target="TimeStampOption"></xref>. The Timestamp field SHOULD be set to
the current time, according to sender's real time clock.</t>
<t>For the received Encrypted-Response message, the client extracts the
encrypted-message option and decrypts it using its private key to obtain
the original DHCPv6 message. Then it handles the message as per <xref
target="RFC3315"></xref>. If the client fails to get the proper
parameters from the chosen server, it sends the Encrypted-Query message
to another authenticated server for parameters configuration until the
client obtains the proper parameters.</t>
<t>When the client receives a Reply message with an error status code,
the error status code indicates the failure reason on the server side.
According to the received status code, the client MAY take follow-up
action:</t>
<t><list style="symbols">
<t>Upon receiving an AlgorithmNotSupported error status code, the
client SHOULD resend the message protected with one of the mandatory
algorithms.</t>
<t>Upon receiving an AuthenticationFail error status code, the
client is not able to build up the secure communication with the
recipient. However, there may be other DHCPv6 servers available that
successfully complete authentication. The client MAY use the
AuthenticationFail as a hint and switch to other public key
certificate if it has another one; but otherwise treat the message
containing the status code as if it had not been received. But it
SHOULD NOT retry with the same certificate. However, if the client
decides to retransmit using the same certificate after receiving
AuthenticationFail, it MUST NOT retransmit immediately and MUST
follow normal retransmission routines defined in <xref
target="RFC3315"></xref>.</t>
<t>Upon receiving a TimestampFail error status code, the client MAY
resend the message with an adjusted timestamp according to the
returned clock from the DHCPv6 server. The client SHOULD NOT change
its own clock, but only compute an offset for the communication
session.</t>
<t>Upon receiving a SignatureFail error status code, the client MAY
resend the message following normal retransmission routines defined
in <xref target="RFC3315"></xref>.</t>
</list></t>
</section>
<section title="DHCPv6 Server Behavior">
<t>For the secure DHCPv6 server, it also MUST have a public certificate.
The server may be pre-configured a public key certificate, which is
signed by a CA trusted by the server, and its corresponding private
key.</t>
<t>When the DHCPv6 server receives the Information-request message and
the contained Option Request option informs the request for the server
authentication information, it replies the Reply message to the client.
The reply message MUST contain the requested certificate option, which
MUST be constructed as explained in <xref target="CertOption"></xref>.
In addition, the Reply message MUST contain one and only one Signature
option, which MUST be constructed as explained in <xref
target="SigOption"></xref>. It protects the message header and all
DHCPv6 options except for the Authentication Option. Besides, the Reply
message SHOULD contain one and only one Timestamp option, which MUST be
constructed as explained in <xref target="TimeStampOption"></xref>. The
Timestamp field SHOULD be set to the current time, according to server's
real time clock.</t>
<t>Upon the receipt of Encrypted-Query message, the server checks the
server identifier option. It decrypts the encrypted-message option using
its private key if it is the target server. The DHCPv6 server drops the
message that is not for it, thus not paying cost to decrypt the
message.</t>
<t>If the decrypted message is Solicit/Information-request message, the
secure DHCPv6 server SHOULD discard the received message that meet any
of the following conditions:<list style="symbols">
<t>the signature option is missing,</t>
<t>multiple signature options are present,</t>
<t>the certificate option is missing.</t>
</list></t>
<t>In such failure, the server SHOULD reply an UnspecFail (value 1,
<xref target="RFC3315"></xref>) error status code.</t>
<t>The server SHOULD first check the support of the hash and signature
algorithms that the client used. If the check fails, the server SHOULD
reply with an AlgorithmNotSupported error status code, defined in <xref
target="StatusCodes"></xref>, back to the client. If both hash and
signature algorithms are supported, the server then checks the authority
of this client.</t>
<t>If a certificate option is provided, the server SHOULD validate the
certificate according to the rules defined in <xref
target="RFC5280"></xref>. An implementation may create a local trust
certificate record for verified certificates in order to avoid repeated
verification procedure in the future. A certificate that finds a match
in the local trust certificate list is treated as verified.</t>
<t>The message that fails certificate validation, MUST be dropped. In
such failure, the DHCPv6 server SHOULD reply an AuthenticationFail error
status code, defined in <xref target="StatusCodes"></xref>, back to the
client. At this point, the server has either recognized the
authentication of the client, or decided to drop the message.</t>
<t>If the server does not send the timestamp option, the client ignores
the timestamp check and verifies the signature. If there is a timestamp
option, the server MUST now authenticate the client by verifying the
signature and checking timestamp (see details in <xref
target="timestampCheck"></xref>). The order of two procedures is left as
an implementation decision. It is RECOMMENDED to check timestamp first,
because signature verification is much more computationally expensive.
Depending on server's local policy, the message without a Timestamp
option MAY be acceptable or rejected. If the server rejects such a
message, a TimestampFail error status code, defined in <xref
target="StatusCodes"></xref>, should be sent back to the client. The
reply message that carries the TimestampFail error status code SHOULD
carry a timestamp option, which indicates the server's clock for the
client to use.</t>
<t>The signature field verification MUST show that the signature has
been calculated as specified in <xref target="SigOption"></xref>. Only
the clients that get through both the signature verification and
timestamp check (if there is a Timestamp option) are accepted as
authenticated clients and continue to be handled their message as
defined in <xref target="RFC3315"></xref>. Clients that do not pass the
above tests MUST be treated as unauthenticated clients. The DHCPv6
server SHOULD reply a SignatureFail error status code, defined in <xref
target="StatusCodes"></xref>, for the signature verification failure; or
a TimestampFail error status code, defined in <xref
target="StatusCodes"></xref>, for the timestamp check failure, back to
the client.</t>
<t>Once the client has been authenticated, the DHCPv6 server sends the
Encrypted-response message to the DHCPv6 client. The Encrypted-response
message contains the encrypted-message option, which MUST be constructed
as explained in <xref target="EncryMesOption"></xref>. The
encrypted-message option contains the encrypted DHCPv6 message that is
encrypted using the authenticated client's public key.</t>
</section>
<section title="Relay Agent Behavior">
<t>When a DHCPv6 relay agent receives an Encrypted-query or
Encrypted-response message, it may not recognize this message. The
unknown messages MUST be forwarded as describes in <xref
target="RFC7283"></xref>.</t>
<t>When a DHCPv6 relay agent recognizes the Encrypted-query and
Encrypted-response messages, it forwards the message according to
section 20 of <xref target="RFC3315"></xref>. There is nothing more the
relay agents have to do, it neither needs to verify the messages from
client or server, nor add any secure DHCPv6 options. Actually, by
definition in this document, relay agents SHOULD NOT add any secure
DHCPv6 options.</t>
<t>Relay-forward and Relay-reply messages MUST NOT contain any
additional certificate option or signature Option or timestamp Option,
aside from those present in the innermost encapsulated messages from the
client or server.</t>
</section>
<section title="Processing Rules">
<section anchor="timestampCheck" title="Timestamp Check">
<t>In order to check the Timestamp option, defined in <xref
target="TimeStampOption"></xref>, recipients SHOULD be configured with
an allowed timestamp Delta value, a "fuzz factor" for comparisons, and
an allowed clock drift parameter. The recommended default value for
the allowed Delta is 300 seconds (5 minutes); for fuzz factor 1
second; and for clock drift, 0.01 second.</t>
<t>Note: the Timestamp mechanism is based on the assumption that
communication peers have roughly synchronized clocks, with certain
allowed clock drift. So, accurate clock is not necessary. If one has a
clock too far from the current time, the timestamp mechanism would not
work.</t>
<t>To facilitate timestamp checking, each recipient SHOULD store the
following information for each sender, from which at least one
accepted secure DHCPv6 message is successfully verified (for both
timestamp check and signature verification):</t>
<t><list style="symbols">
<t>The receive time of the last received and accepted DHCPv6
message. This is called RDlast.</t>
<t>The timestamp in the last received and accepted DHCPv6 message.
This is called TSlast.</t>
</list>A verified (for both timestamp check and signature
verification) secure DHCPv6 message initiates the update of the above
variables in the recipient's record.</t>
<t>Recipients MUST check the Timestamp field as follows:</t>
<t><list style="symbols">
<t>When a message is received from a new peer (i.e., one that is
not stored in the cache), the received timestamp, TSnew, is
checked, and the message is accepted if the timestamp is recent
enough to the reception time of the packet, RDnew:<list
style="empty">
<t>-Delta < (RDnew - TSnew) < +Delta</t>
</list><vspace blankLines="1" />After the signature verification
also succeeds, the RDnew and TSnew values SHOULD be stored in the
cache as RDlast and TSlast.</t>
<t>When a message is received from a known peer (i.e., one that
already has an entry in the cache), the timestamp is checked
against the previously received Secure DHCPv6 message:<list
style="empty">
<t>TSnew + fuzz > TSlast + (RDnew - RDlast) x (1 - drift) -
fuzz</t>
</list><vspace blankLines="1" />If this inequality does not hold
or RDnew < RDlast, the recipient SHOULD silently discard the
message. If, on the other hand, the inequality holds, the
recipient SHOULD process the message. <vspace
blankLines="1" />Moreover, if the above inequality holds and TSnew
> TSlast, the recipient SHOULD update RDlast and TSlast after
the signature verification also successes. Otherwise, the
recipient MUST NOT update RDlast or TSlast.</t>
</list>An implementation MAY use some mechanism such as a timestamp
cache to strengthen resistance to replay attacks. When there is a very
large number of nodes on the same link, or when a cache filling attack
is in progress, it is possible that the cache holding the most recent
timestamp per sender will become full. In this case, the node MUST
remove some entries from the cache or refuse some new requested
entries. The specific policy as to which entries are preferred over
others is left as an implementation decision.</t>
<t>An implementation MAY statefully record the latest timestamps from
senders. In such implementation, the timestamps MUST be strictly
monotonously increasing. This is reasonable given that DHCPv6 messages
are rarely misordered.</t>
</section>
</section>
<section title="Extensions for Secure DHCPv6">
<t>This section describes the extensions to DHCPv6. Five new DHCPv6
options, two new DHCPv6 messages and five status codes are defined.</t>
<section title="New DHCPv6 Options">
<section anchor="CertOption" title="Certificate Option">
<t>The certificate option carries the public key certificate of the
client/server. The format of the certificate option is described as
follows:</t>
<t><figure align="center">
<artwork><![CDATA[ 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_CERTIFICATE | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. Certificate (variable length) .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
option-code OPTION_CERTIFICATE (TBA1).
option-len Length of certificate in octets.
Certificate A variable-length field containing certificate. The
encoding of certificate and certificate data MUST
be in format as defined in Section 3.6, [RFC7296].
The support of X.509 certificate - Signature (4)
is mandatory.
]]></artwork>
</figure></t>
</section>
<section anchor="SigOption" title="Signature Option">
<t>The signature option allows a signature that is signed by the
private key to be attached to a DHCPv6 message. The signature option
could be any place within the DHCPv6 message while it is logically
created after the entire DHCPv6 header and options, except for the
Authentication Option. It protects the entire DHCPv6 header and
options, including itself, except for the Authentication Option. The
format of the Signature option is described as follows:</t>
<t><figure align="center">
<artwork><![CDATA[ 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_SIGNATURE | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| HA-id | SA-id | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| |
. Signature (variable length) .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
option-code OPTION_SIGNATURE (TBA2).
option-len 2 + Length of Signature field in octets.
HA-id Hash Algorithm id. The hash algorithm is used for
computing the signature result. This design is
adopted in order to provide hash algorithm agility.
The value is from the Hash Algorithm for Secure
DHCPv6 registry in IANA. The support of SHA-256 is
mandatory. A registry of the initial assigned values
is defined in Section 8.
SA-id Signature Algorithm id. The signature algorithm is
used for computing the signature result. This
design is adopted in order to provide signature
algorithm agility. The value is from the Signature
Algorithm for Secure DHCPv6 registry in IANA. The
support of RSASSA-PKCS1-v1_5 is mandatory. A
registry of the initial assigned values is defined
in Section 8.
Signature A variable-length field containing a digital
signature. The signature value is computed with
the hash algorithm and the signature algorithm,
as described in HA-id and SA-id. The signature
constructed by using the sender's private key
protects the following sequence of octets:
1. The DHCPv6 message header.
2. All DHCPv6 options including the Signature
option (fill the signature field with zeroes)
except for the Authentication Option.
The signature field MUST be padded, with all 0, to
the next octet boundary if its size is not a
multiple of 8 bits. The padding length depends on
the signature algorithm, which is indicated in the
SA-id field.
]]></artwork>
</figure>Note: if both signature and authentication option are
present, signature option does not protect the Authentication
Option. It allows the Authentication Option be created after
signature has been calculated and filled with the valid signature.
It is because both options need to apply hash algorithm to whole
message, so there must be a clear order and there could be only one
last-created option. changing auth option, the authors chose not
include authentication option in the signature.</t>
</section>
<section anchor="TimeStampOption" title="Timestamp Option">
<t>The Timestamp option carries the current time on the sender. It
adds the anti-replay protection to the DHCPv6 messages. It is
optional.</t>
<t><figure>
<artwork><![CDATA[ 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_TIMESTAMP | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Timestamp (64-bit) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
option-code OPTION_TIMESTAMP (TBA3).
option-len 8, in octets.
Timestamp The current time of day (SeND-format timestamp
in UTC (Coordinated Universal Time). It can reduce
the danger of replay attacks.]]></artwork>
</figure></t>
</section>
<section anchor="EncryMesOption" title="Encrypted-message Option">
<t>The encrypted-message option carries the encrypted DHCPv6 message
with the recipient's public key.</t>
<t>The format of the encrypted-message option is:</t>
<figure align="center" anchor="option-dhcpv6-msg"
title="encrypted-message Option Format">
<artwork><![CDATA[
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 | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. encrypted DHCPv6 message .
. (variable) .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
<t><list style="hanging">
<t hangText="option-code">OPTION_ENCRYPTED_MSG (TBA4).</t>
<t hangText="option-len">Length of the encrypted DHCPv6
message.</t>
<t hangText="encrypted DHCPv6 message">A variable length field
containing the encrypted DHCPv6 message sent by the client or
the server. In Encrypted-Query message, it contains encrypted
DHCPv6 message sent by a client. In Encrypted-response message,
it contains encrypted DHCPv6 message sent by a server.</t>
</list></t>
</section>
</section>
<section title="New DHCPv6 Messages">
<section anchor="EncryQueMES" title="Encrypted-Query Message">
<t>The Encrypted-Query message is sent from DHCPv6 client to DHCPv6
server, which contains the server identifier option and
encrypted-message option.</t>
<t>The format of the Encrypted-Query message is:</t>
<figure align="center" anchor="encrypted-query-format"
title="The format of Encrypted-Query Message">
<artwork><![CDATA[
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| msg-type | transaction-id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. DUID .
| (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. encrypted-message option .
. (variable) .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
<t><list hangIndent="16" style="hanging">
<t hangText="msg-type">ENCRYPTED-QUERY (TBA5)</t>
<t hangText="transaction-id">The transaction ID for this message
exchange.</t>
<t hangText="DUID">The DUID for the server.</t>
<t hangText="encrypted-message option">The encrypted DHCPv6
message.</t>
</list></t>
</section>
<section anchor="EncryRespMES" title="Encrypted-Response Message">
<t>The Encrypted-Response message is sent from DHCPv6 server to
DHCPv6 client, which contains the encrypted-message option.</t>
<t>The format of the Encrypted-Response message is:</t>
<figure align="center" anchor="encrypted-response-format"
title="The format of Encrypted-Response Message">
<artwork><![CDATA[
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| msg-type | transaction-id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. encrypted-message option .
. (variable) .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
<t><list hangIndent="16" style="hanging">
<t hangText="msg-type">ENCRYPTED-RESPONSE (TBA6).</t>
<t hangText="transaction-id">The transaction ID for this message
exchange.</t>
<t hangText="encrypted-message option">The encrypted DHCPv6
message.</t>
</list></t>
</section>
</section>
<section anchor="StatusCodes" title="Status Codes">
<t>The following new status codes, see Section 5.4 of <xref
target="RFC3315"></xref> are defined. <list style="symbols">
<t>AlgorithmNotSupported (TBD7): indicates that the DHCPv6 server
does not support algorithms that sender used.</t>
<t>AuthenticationFail (TBD8): indicates that the DHCPv6 client
fails authentication check.</t>
<t>TimestampFail (TBD9): indicates the message from DHCPv6 client
fails the timestamp check.</t>
<t>SignatureFail (TBD10): indicates the message from DHCPv6 client
fails the signature check.</t>
</list></t>
</section>
</section>
<section anchor="Security" title="Security Considerations">
<t>This document provides the authentication and encryption mechanisms
for DHCPv6.</t>
<t><xref target="RFC6273"></xref> has analyzed possible threats to the
hash algorithms used in SEND. Since the Secure DHCPv6 defined in this
document uses the same hash algorithms in similar way to SEND, analysis
results could be applied as well: current attacks on hash functions do
not constitute any practical threat to the digital signatures used in
the signature algorithm in the Secure DHCPv6.</t>
<t>A server, whose local policy accepts messages without a Timestamp
option, may have to face the risk of replay attacks.</t>
<t>A window of vulnerability for replay attacks exists until the
timestamp expires. Secure DHCPv6 nodes are protected against replay
attacks as long as they cache the state created by the message
containing the timestamp. The cached state allows the node to protect
itself against replayed messages. However, once the node flushes the
state for whatever reason, an attacker can re-create the state by
replaying an old message while the timestamp is still valid. In
addition, the effectiveness of timestamps is largely dependent upon the
accuracy of synchronization between communicating nodes. However, how
the two communicating nodes can be synchronized is out of scope of this
work.</t>
<t>Attacks against time synchronization protocols such as NTP [RFC5905]
may cause Secure DHCPv6 nodes to have an incorrect timestamp value. This
can be used to launch replay attacks, even outside the normal window of
vulnerability. To protect against these attacks, it is recommended that
Secure DHCPv6 nodes keep independently maintained clocks or apply
suitable security measures for the time synchronization protocols.</t>
</section>
<section anchor="IANA" title="IANA Considerations">
<t>This document defines five new DHCPv6 <xref target="RFC3315"></xref>
options. The IANA is requested to assign values for these five options
from the DHCPv6 Option Codes table of the DHCPv6 Parameters registry
maintained in http://www.iana.org/assignments/dhcpv6-parameters. The
five options are:</t>
<t><list style="empty">
<t>The Certificate Option (TBA1), described in <xref
target="CertOption"></xref>.</t>
<t>The Signature Option (TBA2), described in <xref
target="SigOption"></xref>.</t>
<t>The Timestamp Option (TBA3),described in <xref
target="TimeStampOption"></xref>.</t>
<t>The Encrypted-message Option (TBA4), described in <xref
target="EncryMesOption"></xref>.</t>
</list></t>
<t>The IANA is also requested to assign value for these two messages
from the DHCPv6 Message Types table of the DHCPv6 Parameters registry
maintained in http://www.iana.org/assignments/dhcpv6-parameters. The two
messages are:</t>
<t><list style="empty">
<t>The Encrypted-Query Message (TBA5), described in <xref
target="EncryQueMES"></xref>.</t>
<t>The Encrypted-Response Message (TBA6), described in <xref
target="EncryRespMES"></xref>.</t>
</list></t>
<t>The IANA is also requested to add two new registry tables to the
DHCPv6 Parameters registry maintained in
http://www.iana.org/assignments/dhcpv6-parameters. The two tables are
the Hash Algorithm for Secure DHCPv6 table and the Signature Algorithm
for Secure DHCPv6 table.</t>
<t>Initial values for these registries are given below. Future
assignments are to be made through Standards Action <xref
target="RFC5226"></xref>. Assignments for each registry consist of a
name, a value and a RFC number where the registry is defined.</t>
<t>Hash Algorithm for Secure DHCPv6. The values in this table are 8-bit
unsigned integers. The following initial values are assigned for Hash
Algorithm for Secure DHCPv6 in this document:</t>
<t><figure>
<artwork><![CDATA[ Name | Value | RFCs
-------------------+---------+--------------
SHA-256 | 0x01 | this document
SHA-512 | 0x02 | this document
]]></artwork>
</figure>Signature Algorithm for Secure DHCPv6. The values in this
table are 8-bit unsigned integers. The following initial values are
assigned for Signature Algorithm for Secure DHCPv6 in this document:</t>
<t><figure>
<artwork><![CDATA[ Name | Value | RFCs
-------------------+---------+--------------
RSASSA-PKCS1-v1_5 | 0x01 | this document
]]></artwork>
</figure>IANA is requested to assign the following new DHCPv6 Status
Codes, defined in <xref target="StatusCodes"></xref>, in the DHCPv6
Parameters registry maintained in
http://www.iana.org/assignments/dhcpv6-parameters:</t>
<t><figure>
<artwork><![CDATA[ Code | Name | Reference
---------+-----------------------+--------------
TBD7 | AlgorithmNotSupported | this document
TBD8 | AuthenticationFail | this document
TBD9 | TimestampFail | this document
TBD10 | SignatureFail | this document
]]></artwork>
</figure></t>
</section>
<section anchor="Acknowledgments" title="Acknowledgements">
<t>The authors would like to thank Tomek Mrugalski, Bernie Volz, Randy
Bush, Yiu Lee, Jianping Wu, Sean Shen, Ralph Droms, Jari Arkko, Sean
Turner, Stephen Farrell, Christian Huitema, Stephen Kent, Thomas Huth,
David Schumacher, Francis Dupont, Gang Chen, Suresh Krishnan, Fred
Templin, Robert Elz, Nico Williams, Erik Kline, Alan DeKok, Bernard
Aboba, Sam Hartman, Qi Sun, Zilong Liu, and other members of the IETF
DHC working group for their valuable comments.</t>
<t>This document was produced using the xml2rfc tool <xref
target="RFC2629"></xref>.</t>
</section>
</middle>
<back>
<references title="Normative References">
<?rfc include='reference.RFC.2119'?>
<?rfc include='reference.RFC.2460'?>
<?rfc include='reference.RFC.3315'?>
<?rfc include='reference.RFC.4443'?>
<?rfc include='reference.RFC.5280'?>
<?rfc include='reference.RFC.5905'?>
<?rfc include='reference.RFC.7296'?>
<?rfc include='reference.RFC.7283'?>
</references>
<references title="Informative References">
<reference anchor="RSA">
<front>
<title>RSA Encryption Standard, Version 2.1, PKCS 1</title>
<author fullname="">
<organization>RSA Laboratories</organization>
</author>
<date month="November" year="2002" />
</front>
</reference>
<?rfc include='reference.RFC.2629'?>
<?rfc include='reference.RFC.4270'?>
<?rfc include='reference.RFC.5226'?>
<?rfc include='reference.RFC.6273'?>
<?rfc include='reference.RFC.7258'?>
</references>
</back>
</rfc>
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