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Versions: 00 01 02 draft-ietf-dhc-sedhcpv6

DHC Working Group                                               S. Jiang
Internet-Draft                              Huawei Technologies Co., Ltd
Intended status: Standards Track                                 S. Shen
Expires: April 11, 2014                                            CNNIC
                                                        October 08, 2013


                     Secure DHCPv6 with Public Key
                      draft-jiang-dhc-sedhcpv6-01

Abstract

   The Dynamic Host Configuration Protocol for IPv6 (DHCPv6) enables
   DHCPv6 servers to pass configuration parameters.  It offers
   configuration flexibility.  If not secured, DHCPv6 is vulnerable to
   various attacks, particularly spoofing attacks.  This document
   analyzes the security issues of DHCPv6 and specifies a Secure DHCPv6
   mechanism.  This mechanism is based on public/private key pairs.  The
   authority of the sender may depend on either pre-configuration
   mechanism or Public Key Infrastructure.

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 11, 2014.

Copyright Notice

   Copyright (c) 2013 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
   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



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   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language and Terminology . . . . . . . . . . . .   3
   3.  Security Overview of DHCPv6 . . . . . . . . . . . . . . . . .   3
   4.  Secure DHCPv6 Overview  . . . . . . . . . . . . . . . . . . .   4
     4.1.  New Components  . . . . . . . . . . . . . . . . . . . . .   5
     4.2.  Support for algorithm agility . . . . . . . . . . . . . .   5
   5.  Extensions for Secure DHCPv6  . . . . . . . . . . . . . . . .   6
     5.1.  Public Key Option . . . . . . . . . . . . . . . . . . . .   6
     5.2.  Certificate Option  . . . . . . . . . . . . . . . . . . .   6
     5.3.  Signature Option  . . . . . . . . . . . . . . . . . . . .   7
   6.  Processing Rules and Behaviors  . . . . . . . . . . . . . . .   8
     6.1.  Processing Rules of Sender  . . . . . . . . . . . . . . .   8
     6.2.  Processing Rules of Recipient . . . . . . . . . . . . . .   9
     6.3.  Processing Rules of Relay Agent . . . . . . . . . . . . .  11
     6.4.  Timestamp Check . . . . . . . . . . . . . . . . . . . . .  11
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  12
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  14
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  14
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  14
     10.2.  Informative References . . . . . . . . . . . . . . . . .  15
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  15

1.  Introduction

   The Dynamic Host Configuration Protocol for IPv6 (DHCPv6, [RFC3315])
   enables DHCPv6 servers to pass configuration parameters.  It offers
   configuration flexibility.  If not secured, DHCPv6 is vulnerable to
   various attacks, particularly spoofing attacks.

   This document analyzes the security issues of DHCPv6 in details.
   This document provides mechanisms for improving the security of
   DHCPv6:

   o  the identity of a DHCPv6 message sender, which can be a DHCPv6
      server, a relay agent or a client, can be verified by a recipient.

   o  the integrity of DHCPv6 messages can be checked by the recipient
      of the message.





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   The security mechanisms specified in this document is based on self-
   generated public/private key pairs.  It also integrates timestamps
   for anti-replay.  The authentication procedure defined in this
   document may depend on either deployed Public Key Infrastructure
   (PKI, [RFC5280]) or pre-configured sender's public key.  However, the
   deployment of PKI or pre-configuration is out of the scope.

   Secure DHCPv6 is applicable in environments where physical security
   on the link is not assured (such as over wireless) and attacks on
   DHCPv6 are a concern.

2.  Requirements Language and Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   [RFC2119] 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 [RFC2119] key
   words.

3.  Security Overview of DHCPv6

   DHCPv6 is a client/server protocol that provides managed
   configuration of devices.  It enables DHCPv6 server to automatically
   configure relevant network parameters on clients.  In the basic
   DHCPv6 specification [RFC3315], security of DHCPv6 message can be
   improved in a few respects.

   a.  The basic DHCPv6 specifications can optionally authenticate the
       origin of messages and validate the integrity of messages using
       an authentication option with a symmetric key pair.  [RFC3315]
       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; [RFC3315] provides no
       mechanism for doing this.

       For the key of the hash function, there are two key management
       mechanisms.  Firstly, the key management is done out of band,
       usually through some manual process.  For example, operators can
       set up a key database for both servers and clients which the
       client obtains a key before running DHCPv6.









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       Manual key distribution runs counter to the goal of minimizing
       the configuration data needed at each host.  [RFC3315] provides
       an additional mechanism for preventing off-network timing attacks
       using the Reconfigure message: the Reconfigure Key authentication
       method.  However, this method provides no message integrity or
       source integrity check.  This key is transmitted in plaintext.

       In comparison, the public/private key security mechanism allows
       the keys to be generated by the sender, and allows the public key
       database on the recipient to be populated opportunistically or
       manually, depending on the degree of confidence desired in a
       specific application.  PKI security mechanism is simpler in the
       local key management respect.

   b.  Communication between a server and a relay agent, and
       communication between relay agents, can be secured through the
       use of IPsec, as described in section 21.1 in [RFC3315].
       However, IPsec is quite complicated.  A simpler security
       mechanism, which can be easier to deploy, is desirable.

4.  Secure DHCPv6 Overview

   To solve the above mentioned security issues, we introduce the use of
   public/private key pair mechanism into DHCPv6, also with timestamp.
   The authority of the sender may depend on either pre-configuration
   mechanism or PKI.  By combining with the signatures, sender identity
   can be verified and messages protected.

   This document introduces a Secure DHCPv6 mechanism that uses a public
   /private key pair to secure the DHCPv6 protocol.  It has two modes;
   in both modes, the sender has a public/private key pair.  In the
   first mode, the public key of the sender is pre-shared with the
   recipient, either opportunistically or through a manual process.  In
   the second mode, the sender has a certificate for its public key,
   signed by a Certificate Authority that is trust by the recipient.  It
   is possible for the same public key to be used with different
   recipients in both modes.

   In this document, we introduce a public key option, a certificate
   option and a signature options with a corresponding verification
   mechanism.  Timestamp is integrated into signature options.  A DHCPv6
   message (from a server, a relay agent or a client), with either a
   public key or certificate option, and carrying a digital signature,
   can be verified by the recipient for both the timestamp and
   authentication, then process the payload of the DHCPv6 message only
   if the validation is successful.





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   This improves communication security of DHCPv6 messages.  The
   authentication options [RFC3315] may also be used for replay
   protection.

   Because the sender can be a DHCPv6 server, a relay agent or a client,
   the end-to-end security protection can be from DHCPv6 servers to
   relay agents or clients, or from clients to DHCPv6 servers.  Relay
   agents MAY add its own Secure DHCPv6 options in Relay-Forward
   messages when transmitting client messages to the server.

4.1.  New Components

   The components of the solution specified in this document are as
   follows:

   o  The node generates a public/private key pair.  A DHCPv6 option is
      defined that carries the public key.

      The node may also obtain a certificate from a Certificate
      Authority that can be used to establish the trustworthiness of the
      node.  A second option is defined to carry the certificate.
      Because the certificate contains the public key, there is never a
      need to send both options at the same time.

   o  A signature generated using the private key that protects the
      integrity of the DHCPv6 messages and authenticates the identity of
      the sender.

   o  A timestamp, to detect and prevent packet replay.  The secure
      DHCPv6 nodes 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.

4.2.  Support for algorithm agility

   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
   [RFC4270], this document provides a mechanism for negotiating the use
   of more secure hashes in the future.

   In addition to hash algorithm agility, this document also provides a
   mechanism for signature algorithm agility.








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   The support for algorithm agility in this document is mainly a
   unilateral notification mechanism from sender to recipient.  If the
   recipient does not support the algorithm used by the sender, it
   cannot authenticate the message.  Senders in a same administrative
   domain are not required to upgrade to a new algorithm simultaneously.

5.  Extensions for Secure DHCPv6

   This section extends DHCPv6.  Three new options have been defined.
   The new options MUST be supported in the Secure DHCPv6 message
   exchange.

5.1.  Public Key Option

   The Public Key option carries the public key of the sender.  The
   format of the Public Key option is described as follows:

      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_Public_Key        |         option-len            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     .                     Public Key (variable length)              .
     .                                                               .
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     option-code    OPTION_PK_PARAMETER (TBA1).

     option-len     Length of public key in octets.

     Public Key     A variable-length field containing public key.


5.2.  Certificate Option

   The Certificate option carries the certificate of the sender.  The
   format of the Certificate option is described as follows:

      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)              .
     .                                                               .
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



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     option-code    OPTION_CERT_PARAMETER (TBA2).

     option-len     Length of certificate in octets.

     Certificate    A variable-length field containing certificate.


5.3.  Signature Option

   The Signature option allows public key-based signatures to be
   attached to a DHCPv6 message.  The Signature option could be any
   place within the DHCPv6 message.  It protects the entire DHCPv6
   header and options, except for the Authentication Option.  The format
   of the Signature option is described as follows:

     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              |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                     Timestamp (64-bit)                        |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    .                    Signature (variable length)                .
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    option-code    OPTION_SIGNATURE (TBA3).

    option-len     12 + 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 initial values are
                   assigned for SHA-1 is 0x0001.

    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
                   initial values are assigned for RSASSA-PKCS1-v1_5
                   is 0x0001.



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    Timestamp      The current time of day (NTP-format timestamp
                   [RFC5905] in UTC (Coordinated Universal Time), a
                   64-bit unsigned fixed-point number, in seconds
                   relative to 0h on 1 January 1900.). It can reduce
                   the danger of replay attacks.

    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 filed MUST be padded, with all 0, to
                   the next octet boundary if its size is not an even
                   multiple of 8 bits. The padding length depends on
                   the signature algorithm, which is indicated in the
                   SA-id field.


6.  Processing Rules and Behaviors

6.1.  Processing Rules of Sender

   The sender of a Secure DHCPv6 message could be a DHCPv6 server, a
   DHCPv6 relay agent or a DHCPv6 client.

   The node must have a public/private key pair in order to create
   Secure DHCPv6 messages.  The node may have a certificate which is
   signed by a CA trusted by both sender and recipient.

   To support Secure DHCPv6, the Secure DHCPv6 enabled sender MUST
   construct the DHCPv6 message following the rules defined in
   [RFC3315].

   A Secure DHCPv6 message MUST contain the Signature option, in which
   Timestamp field MUST be set correctly, either a Public Key or
   Certificate option, except for Relay-forward and Relay-reply
   Messages.  The Timestamp field SHOULD be set to the current time,
   according to sender's real time clock.





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   If a relay agent adds its own options in a Relay-forward message, it
   MAY contain a Signature option and one of a Public Key or Certificate
   option.  If it does not any add new options it MUST NOT add any
   Public Key or Certificate or Signature option into Relay-forward
   message.  If there are more than a number of Relay agents (the number
   depends on the lengths of public key and signature, typical number is
   four) in the way and each of them adds their own options, it may
   exceed the IPv6 MTU.  However, this can be considered as a rare
   deployment scenario.

   Relay-reply Messages MUST NOT contain any Public Key or Certificate
   option since it appears in the Relay Message Option.  If a server
   adds addition options for relay agents in Relay-reply message, it MAY
   contain a Signature Option.  If it does not add any addition options,
   it MUST NOT add the Signature Option into the Relay-reply message.

   The Signature option MUST be constructed as explained in Section 5.3.
   It protects the message header and the message payload and all DHCPv6
   options except for the Signature option itself and the Authentication
   Option.

6.2.  Processing Rules of Recipient

   When receiving a DHCPv6 message (except for Relay-Forward and Relay-
   Reply messages), a Secure DHCPv6 enabled recipient SHOULD discard the
   DHCPv6 message if the Signature option is absent, or both the Public
   Key and Certificate option is absent, or both the Public Key and
   Certificate option are presented.  If all three options are absent,
   the recipient MAY fall back the unsecure DHCPv6 model.

   The recipient SHOULD first check the authority of this sender.  If
   the sender uses a public key, the recipient SHOULD validate it by
   finding a match public key from the local trust public key list,
   which is pre-configured or recorded from previous communications.  If
   the sender uses certificate, the recipient SHOULD validate the
   sender's certificate following the rules defined in [RFC5280].  An
   implementation may then create a local trust certificate record.

   The recipient may choose to further process the message from a sender
   for which no authorization information exists.  By recording the key
   that was used by the sender, when the first time it is seen, the
   recipient can make a leap of faith that the sender is trustworthy.
   If no evidence to the contrary surfaces, the recipient can then
   validate the sender as trustworthy when it subsequently sees the same
   key used to sign messages from the same server.

   At this point, the recipient has either recognized the authorization
   of the sender, or decided to attempt a leap of faith.  The recipient



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   MUST now authenticate the sender by verifying the Signature and
   checking timestamp.  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.

   The signature field verification MUST show that the signature has
   been calculated as specified in Section 5.3.  Only the messages that
   get through both the signature verifications and timestamp check are
   accepted as secured DHCPv6 messages and continue to be handled for
   their contained DHCPv6 options as defined in [RFC3315].  Messages
   that do not pass the above tests MUST be discarded or treated as
   unsecure messages.

   The recipient MAY record the verified public key or certificate for
   future authentications.

   Furthermore, the node that supports the verification of the Secure
   DHCPv6 messages MAY record the following information:

   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 [RSA].

   A Relay-forward message without any addition option to Relay Message
   option or a Relay-forward message with both addition options and the
   Signature option is accepted for a Secure DHCPv6 enabled server.
   Otherwise, the message SHOULD be discarded or treated as unsecure
   message.  If Signature option is presented in the Relay-forward
   message, the signature verification and timestamp check are needed.
   The server MUST also verify signature for the encapsulated client
   DHCPv6 message in the Relay Message Option.

   A Relay-reply message without any addition option to Relay Message
   option or a Relay-reply message with both addition options and the
   Signature Option is accepted for a Secure DHCPv6 enabled server.
   Otherwise, the message SHOULD be discarded or treated as unsecure
   message.  If the Signature Option is presented in the Relay-reply
   message, the signature verification and timestamp check are needed.
   The relay agents obtain the public key or certificate of the server
   from the Public Key or Certificate option encapsulated in the Relay
   Message option.





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6.3.  Processing Rules of Relay Agent

   To support Secure DHCPv6, relay agents MUST follow the same
   processing rules defined in [RFC3315].

   In the client-relay-server scenario, the relay agent MAY verify the
   signature as a recipient before relaying the client message further,
   following verification procedure define in Section 6.2.  In the case
   of failure, it MUST discard the DHCPv6 message.  However, the
   verification procedure on relay agents does not save the load of the
   DHCPv6 server.  The server still MUST verify the signature by itself
   in order to prevent the attack between the relay agent and server.

   In the server-relay-client scenario, if the Signature Option and
   addition options are presented, the relay agent MUST verify the
   signature before relaying the server message further, following
   verification procedure define in Section 6.2.  In the case of
   failure, it MUST discard the DHCPv6 message.

   The relay agent MAY also verify the signature for the encapsulated
   DHCPv6 message in the Relay Message Option.  This can be helpful if
   the DHCPv6 response traverses a separate administrative domain, or if
   the relay agent is in a separate administrative domain.  However,
   this is not necessary because the DHCPv6 client validation will catch
   any modification to the response.

6.4.  Timestamp Check

   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.

   To facilitate timestamp checking, each recipient SHOULD store the
   following information for each sender:

   o  The receive time of the last received and accepted DHCPv6 message.
      This is called RDlast.

   o  The time stamp in the last received and accepted DHCPv6 message.
      This is called TSlast.

   An accepted secure DHCPv6 message is any successfully verified (for
   both timestamp check and signature verification) DHCPv6 message from
   the given peer.  It initiates the update of the above variables.

   Recipients MUST then check the Timestamp field as follows:



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   o  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:

         -Delta < (RDnew - TSnew) < +Delta

      The RDnew and TSnew values SHOULD be stored in the cache as RDlast
      and TSlast.

   o  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:

         TSnew + fuzz > TSlast + (RDnew - RDlast) x (1 - drift) - fuzz

      If this inequality does not hold, the recipient SHOULD silently
      discard the message.  If, on the other hand, the inequality holds,
      the recipient SHOULD process the message.

      Moreover, if the above inequality holds and TSnew > TSlast, the
      recipient SHOULD update RDlast and TSlast.  Otherwise, the
      recipient MUST NOT update RDlast or TSlast.

   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.

7.  Security Considerations

   This document provides new security features to the DHCPv6 protocol.

   Using public key based security mechanism and its verification
   mechanism in DHCPv6 message exchanging provides the authentication
   and data integrity protection.  Timestamp mechanism provides anti-
   replay function.

   The Secure DHCPv6 mechanism is based on the pre-condition that the
   recipient knows the public key of senders or the sender's certificate
   can be verified through a trust CA.  It prevents DHCPv6 server
   spoofing.  The clients may decline the DHCPv6 messages from unknown/
   unverified servers, which may be fake servers; or may prefer DHCPv6
   messages from known/verified servers over unsigned messages or



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   messages from unknown/unverified servers.  The pre-configuration
   operation also needs to be protected, which is out of scope.  The
   deployment of PKI is also out of scope.

   However, when a DHCPv6 client first encounters a new public key or
   new unverified certificate, it can make a leap of faith.  If the
   DHCPv6 server that used that public key or certificate is in fact
   legitimate, then all future communication with that DHCPv6 server can
   be protected by caching the public key.  This does not provide
   complete security, but it limits the opportunity to mount an attack
   on a specific DHCPv6 client to the first time it communicates with a
   new DHCPv6 server.

   Downgrade attacks cannot be avoided if nodes are configured to accept
   both secured and unsecured messages.  A future specification may
   provide a mechanism on how to treat unsecured DHCPv6 messages.

   [RFC6273] 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.

   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.

   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.

8.  IANA Considerations

   This document defines three new DHCPv6 [RFC3315] options.  The IANA
   is requested to assign values for these three options from the DHCP
   Option Codes table of the DHCPv6 Parameters registry.  The three
   options are:

      The Public Key Option (TBA1), described in Section 5.1.



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      The Certificate Option (TBA2), described in Section 5.2.

      The Signature Option (TBA3), described in Section 5.3.

   The IANA is also requested to add two new registry tables to the
   DHCPv6 Parameters registry.  The two tables are the Hash Algorithm
   for Secure DHCPv6 table and the Signature Algorithm for Secure DHCPv6
   table.

   Initial values for these registries are given below.  Future
   assignments are to be made through Standards Action [RFC5226].
   Assignments for each registry consist of a name, a value and a RFC
   number where the registry is defined.

   Hash Algorithm for Secure DHCPv6.  The values in this table are
   16-bit unsigned integers.  The following initial values are assigned
   for Hash Algorithm for Secure DHCPv6 in this document:

          Name        |  Value  |  RFCs
   -------------------+---------+------------
         Reserved     |  0x0000 | this document
         SHA-1        |  0x0001 | this document
         SHA-256      |  0x0002 | this document


   Signature Algorithm for Secure DHCPv6.  The values in this table are
   16-bit unsigned integers.  The following initial values are assigned
   for Signature Algorithm for Secure DHCPv6 in this document:

          Name        |  Value  |  RFCs
   -------------------+---------+------------
         Reserved     |  0x0000 | this document
    RSASSA-PKCS1-v1_5 |  0x0001 | this document


9.  Acknowledgements

   The authors would like to thank Bernie Volz, Ted Lemon, Ralph Droms,
   Jari Arkko, Sean Turner, Stephen Kent, Thomas Huth, David Schumacher,
   Dacheng Zhang, Francis Dupont and other members of the IETF DHC
   working groups for their valuable comments.

   This document was produced using the xml2rfc tool [RFC2629].

10.  References

10.1.  Normative References




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   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3315]  Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
              and M. Carney, "Dynamic Host Configuration Protocol for
              IPv6 (DHCPv6)", RFC 3315, July 2003.

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, May 2008.

   [RFC5905]  Mills, D., Martin, J., Burbank, J., and W. Kasch, "Network
              Time Protocol Version 4: Protocol and Algorithms
              Specification", RFC 5905, June 2010.

10.2.  Informative References

   [RFC2629]  Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629,
              June 1999.

   [RFC4270]  Hoffman, P. and B. Schneier, "Attacks on Cryptographic
              Hashes in Internet Protocols", RFC 4270, November 2005.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.

   [RFC6273]  Kukec, A., Krishnan, S., and S. Jiang, "The Secure
              Neighbor Discovery (SEND) Hash Threat Analysis", RFC 6273,
              June 2011.

   [RSA]      RSA Laboratories, "RSA Encryption Standard, Version 2.1,
              PKCS 1", November 2002.

   [sha-1]    National Institute of Standards and Technology, "Secure
              Hash Standard, FIBS PUB 180-1", April 1995,
              <http://www.itl.nist.gov/fipspubs/fip180-1.htm>.

Authors' Addresses

   Sheng Jiang
   Huawei Technologies Co., Ltd
   Q14, Huawei Campus, No.156 Beiqing Road
   Hai-Dian District, Beijing, 100095
   P.R. China

   Email: jiangsheng@huawei.com



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   Sean Shen
   CNNIC
   4, South 4th Street, Zhongguancun
   Beijing  100190
   P.R. China

   Email: shenshuo@cnnic.cn












































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