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Versions: (draft-jiang-dhc-sedhcpv6) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21

DHC Working Group                                          S. Jiang, Ed.
Internet-Draft                              Huawei Technologies Co., Ltd
Intended status: Standards Track                                 S. Shen
Expires: August 18, 2014                                           CNNIC
                                                                D. Zhang
                                            Huawei Technologies Co., Ltd
                                                       February 14, 2014


                     Secure DHCPv6 with Public Key
                       draft-ietf-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 for communication between DHCPv6 client and server.  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 August 18, 2014.

Copyright Notice

   Copyright (c) 2014 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



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   (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
   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
     5.4.  Status Codes  . . . . . . . . . . . . . . . . . . . . . .   9
   6.  Processing Rules and Behaviors  . . . . . . . . . . . . . . .   9
     6.1.  Processing Rules of Sender  . . . . . . . . . . . . . . .   9
     6.2.  Processing Rules of Recipient . . . . . . . . . . . . . .  10
     6.3.  Processing Rules of Relay Agent . . . . . . . . . . . . .  11
     6.4.  Timestamp Check . . . . . . . . . . . . . . . . . . . . .  12
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  13
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  15
   10. Change log [RFC Editor: Please remove]  . . . . . . . . . . .  16
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  16
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  16
     11.2.  Informative References . . . . . . . . . . . . . . . . .  16
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  17

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 between client and server:

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



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

   Note: this secure mechanism in this document does not protect the
   relay-relevant options, either added by a relay agent toward a server
   or added by a server toward a relay agent, are considered less
   vulnerable, because they are only transported within operator
   networks.  Communication between a server and a relay agent, and
   communication between relay agents, may be secured through the use of
   IPsec, as described in section 21.1 in [RFC3315].

   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.

      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.





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      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.

      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.

4.  Secure DHCPv6 Overview

   To solve the above mentioned security issues, this document
   introduces 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 trusted 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 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.  Because the sender can be a DHCPv6 server or a client,
   the end-to-end security protection can be from DHCPv6 servers to or
   clients, or from clients to DHCPv6 servers.



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

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.

   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.  In this case, the receiver SHOULD
   reply with a NotSupportAlgorithm status code (defined in
   Section 5.4).  Upon receiving this status code, the sender MAY resend
   the message protected with the mandatory algorithms (defined in
   Section 5.3).  Therefore, the senders in a same administrative domain
   may be allowed to use various algorithms simultaneously.




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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. The
                  key MUST be represented as a lower-case hexadecimal
                  string with the most significant octet of the key
                  first.

5.2.  Certificate Option

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

















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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_Certificate      |         option-len            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   .                    Certificate (variable length)              .
   .                                                               .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   option-code    OPTION_CERT_PARAMETER (TBA2).

   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, [RFC5996].
                  The support of X.509 certificate is mandatory.

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



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                  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.

   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.

   Note: if both signature and authentication option are presented,
   signature option does not protect authentication option.  It is
   because both needs to apply hash algorithm to whole message, so there
   must be a clear order and there could be only one last-created
   option.  In order to avoid update RFC3315 because of changing auth
   option, the authors chose not include authentication option in the
   signature.




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5.4.  Status Codes

   o  NotSupportAlgorithm (TBD4): Indicates the recipient does not
      support algorthims that sender used.

   o  NotSupportFaithModel (TBD5): Indicates the recipient does not
      support the leap of faith model.

   o  FaithListExceed (TBD6): Indicates the recipient's list that stores
      public keys or unverifiable certificates in the leap of faith
      model currently exceeds.

6.  Processing Rules and Behaviors

6.1.  Processing Rules of Sender

   The sender of a Secure DHCPv6 message could be a DHCPv6 server 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, except for Relay-forward and Relay-reply
   messages, MUST contain either a the Public Key or Certificate option,
   which MUST contructed as explained in Section 5.1 or Section 5.2.

   A Secure DHCPv6 message, except for Relay-forward and Relay-reply
   messages, MUST contain the Signature option, which 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.  Within the
   Signature option the Timestamp field SHOULD be set to the current
   time, according to sender's real time clock.

   A Relay-forward and relay-reply message MUST NOT contain any Public
   Key or Certificate option or Signature Option.

   Upon receiving a Reply message with a NotSupportAlgorithm status
   code, the sender MAY resend the message protected with the mandatory
   algorithms.

   Upon receiving a Reply message with a NotSupportFaithModel or
   FaithListExceed status code, the sender is not able to build up the



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   connection with the recipient.  The sender MAY swith to a verifiable
   certificate.  In the latter case, the sender MAY retry later.

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 support of algorthims that
   sender used.  If not, an error NotSupportAlgorithm status code should
   be sent back to the sender, while the message is dropped siliently.
   If all algorthims are supported, the recipient then checks the
   authority of this sender.

   If the sender uses certificate, the recipient SHOULD validate the
   sender's certificate following the rules defined in [RFC5280].  An
   implementation may create a local trust certificate record for a
   verified certificate in order to avoid repeated verfication procedure
   in the future.  A sender certificate that finds a match in the local
   trust certificate list are treated as verified.  A fast search index
   may be created for this list.

   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.  A
   local trust public key list is a data table maintained by the
   recipient.  It restores public keys from all trustworthy senders.  A
   fast search index may be created for this list.

   The recipient may choose to further process the message from a sender
   for which no authorization information exists, either non-matched
   public key or certificate cannot be verified.  By recording the
   public key or unverifiable certificate 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 public key or certificate used to
   sign messages from the same sender.  If the recipient does not
   support the leap of faith model, it SHOULD reply a message with an
   error NotSupportFaithModel status code, defined in Section 5.4, back
   to the sender.

   The number of cached public keys or unverifiable certificates MUST be
   limited in order to protect the DHCPv6 server against resource



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   exhaustion attacks.  If the recipient's list that stores public keys
   or unverifiable certificates in the leap of faith model exceeds, an
   error FaithListExceed status code SHOULD be returned to the sender.
   The resource releasing policy against exceeding situations is out of
   scope.

   At this point, the recipient has either recognized the authorization
   of the sender, or decided to attempt a leap of faith.  The recipient
   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 or Relay-reply message with any Public Key,
   Certificate or the Signature option is invilad.  The message SHOULD
   be discarded silently.

6.3.  Processing Rules of Relay Agent

   To support Secure DHCPv6, relay agents just need to follow the same
   processing rules defined in [RFC3315].  There is nothing more the
   relay agents have to do, either verify the messages from client or
   server, or add any secure DHCPv6 options.  Actually, be definition in
   this document, relay agents MUST NOT add any secure DHCPv6 options.




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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.

   Note: the Timestamp mechanism is based on the assumption that
   communication peers have rough 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.

   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):

   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 verified (for both timestamp check and signature verification)
   secure DHCPv6 message initiates the update of the above variables in
   the recipient's record.

   Recipients MUST check the Timestamp field as follows:

   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

      After the signature verification also successes, 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





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      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 after the signature
      verification also successes.  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
   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 a
   new unverifiable certificate, it can make a leap of faith.  If the
   DHCPv6 server that used that public key or unverifiable certificate
   is in fact legitimate, then all future communication with that DHCPv6
   server can be protected by storing the public key or unverifiable
   certificate.  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.  The number of
   cached public keys or unverifiable certificates MUST be limited in
   order to protect the DHCPv6 server against resource exhaustion
   attacks.



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   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.
   In addition, the effectiveness of timestamps is largely dependent
   upon the accuracy of synchronization between communicating nodes.
   However, the two communciating nodes can be synchronized is out of
   scope of this work.

   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 maintained in
   http://www.iana.org/assignments/dhcpv6-parameters.  The three options
   are:

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

      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 maintained in http://www.iana.org/
   assignments/dhcpv6-parameters.  The two tables are the Hash Algorithm



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   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
            SHA-512      |  0x0003 | 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

   IANA is requested to assign the following new DHCPv6 Status Codes,
   defined in Section 5.4, in the DHCPv6 Parameters registry maintained
   in http://www.iana.org/assignments/dhcpv6-parameters:

         Code  |          Name        |   Reference
      ---------+----------------------+--------------
         TBD4  |  NotSupportAlgorithm | this document
         TBD5  | NotSupportFaithModel | this document
         TBD6  |    FaithListExceed   | 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,
   Francis Dupont, Tomek Mrugalski, Gang Chen and other members of the
   IETF DHC working groups for their valuable comments.

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





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10.  Change log [RFC Editor: Please remove]

   draft-ietf-dhc-sedhcpv6-00: adopted by DHC WG. 2013-11-19.

   draft-jiang-dhc-sedhcpv6-02: removed protection between relay agent
   and server due to complexity, following the comments from Ted Lemon,
   Bernie Volz. 2013-10-16.

   draft-jiang-dhc-sedhcpv6-01: update according to review comments from
   Ted Lemon, Bernie Volz, Ralph Droms.  Separated Public Key/
   Certificate option into two options.  Refined many detailed
   processes. 2013-10-08.

   draft-jiang-dhc-sedhcpv6-00: original version, this draft is a
   replacement of draft-ietf-dhc-secure-dhcpv6, which reached IESG and
   dead because of consideration regarding to CGA.  The authors followed
   the suggestion from IESG making a general public key based mechanism.
   2013-06-29.

11.  References

11.1.  Normative References

   [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.

   [RFC5996]  Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen,
              "Internet Key Exchange Protocol Version 2 (IKEv2)", RFC
              5996, September 2010.

11.2.  Informative References

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




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   [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.

Authors' Addresses

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

   Email: jiangsheng@huawei.com


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

   Email: shenshuo@cnnic.cn


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

   Email: zhangdacheng@huawei.com










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