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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: December 21, 2014                                         CNNIC
                                                                D. Zhang
                                            Huawei Technologies Co., Ltd
                                                               T. Jinmei
                                                            WIDE Project
                                                           June 19, 2014


                     Secure DHCPv6 with Public Key
                       draft-ietf-dhc-sedhcpv6-03

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 clients and DHCPv6
   servers.  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 December 21, 2014.

Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.




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   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
   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.  Overview of Secure DHCPv6 Mechanism with Public Key . . . . .   4
     4.1.  New Components  . . . . . . . . . . . . . . . . . . . . .   6
     4.2.  Support for algorithm agility . . . . . . . . . . . . . .   6
     4.3.  Applicability . . . . . . . . . . . . . . . . . . . . . .   7
   5.  Extensions for Secure DHCPv6  . . . . . . . . . . . . . . . .   7
     5.1.  Public Key Option . . . . . . . . . . . . . . . . . . . .   7
     5.2.  Certificate Option  . . . . . . . . . . . . . . . . . . .   8
     5.3.  Signature Option  . . . . . . . . . . . . . . . . . . . .   9
     5.4.  Status Codes  . . . . . . . . . . . . . . . . . . . . . .  10
   6.  Processing Rules and Behaviors  . . . . . . . . . . . . . . .  11
     6.1.  Processing Rules of Sender  . . . . . . . . . . . . . . .  11
     6.2.  Processing Rules of Recipient . . . . . . . . . . . . . .  12
     6.3.  Processing Rules of Relay Agent . . . . . . . . . . . . .  14
     6.4.  Timestamp Check . . . . . . . . . . . . . . . . . . . . .  14
   7.  Deployment Consideration  . . . . . . . . . . . . . . . . . .  16
     7.1.  Authentication on a client  . . . . . . . . . . . . . . .  16
     7.2.  Authentication on a server  . . . . . . . . . . . . . . .  16
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  17
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  18
   10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  20
   11. Change log [RFC Editor: Please remove]  . . . . . . . . . . .  20
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  21
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  21
     12.2.  Informative References . . . . . . . . . . . . . . . . .  22
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  22

1.  Introduction

   The Dynamic Host Configuration ProtocoFl 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.




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   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.

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

   o  anti-replay protection based on timestamp checking.

   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.



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   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.

   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.  Overview of Secure DHCPv6 Mechanism with Public Key

   In order to enable a DHCPv6 client and a server mutually authenticate
   each other without previous key deployment, 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.  In order to
   enable DHCPv6 clients and DHCPv6 servers to perform mutual
   authentication, this solution provides two public key based
   mechanisms with different security strengths.  One is stronger and
   only the certificate signed by a trusted CA or preconfigured public
   key can be accepted.  The other one, called as leap of faith (LoF)
   mechanism, is relatively weak.  It allows a client/server pair that
   lacks essential trust relationship to build up their trust
   relationship at run time for subsequent exchanges based on faith.



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   This design simplifies the precondition of deploying DHCPv6
   authentication and provides limited protection of DHCPv6 message.

   In the proposed solution, either public/private key pairs or
   certificates can be used in authentication.  When using public/
   private key pairs directly, the public key of the sender is pre-
   shared with the recipient, either opportunistically or through a
   manual process.  When using certificates, the sender has a
   certificate for its public key, signed by a CA 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 option 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
   clients or from clients to DHCPv6 servers.

   The recipient may choose to further process the message from a sender
   for which no authentication 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.  In opposite, once the recipient
   has determined that it is being attacked, it can either forget that
   sender, or remember that sender in a blacklist and drop further
   packets associated with that sender.

   This improves communication security of DHCPv6 messages.

   Secure DHCPv6 messages are commonly large.  IP fragments [RFC2460]
   are highly possible.  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 configureed to pass ICMP Packet
   Too Big messages [RFC4443].







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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.  Another 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.  The real time provision
      is out of scope.

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.  A
   recipient MAY support various algorithms simultaneously, and the
   differenet senders in a same administrative domain may be allowed to
   use various algorithms simultaneously.

   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 a AlgorithmNotSupported status code
   (defined in Section 5.4).  Upon receiving this status code, the
   client MAY resend the message protected with the mandatory algorithm
   (defined in Section 5.3).




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4.3.  Applicability

   By default, a secure DHCPv6 enabled client SHOULD start with secure
   mode by sending secure DHCPv6 messages.  If the recipient is secure
   DHCPv6 enabled server, their communication would be in secure mode.
   In the scenario where the secure DHCPv6 enabled client and server
   fail to build up secure communication between them, the secure DHCPv6
   enabled client MAY choose to send unsecured DHCPv6 message towards
   the server.

   A secure DHCPv6 enabled server MAY also provide services for
   unsecured clients.  In such case, the resources allocated for
   unsecured clients SHOULD be separated and restricted, in order to
   protect against bidding down attacks.

   In the scenario where the recipient is a legacy DHCPv6 server that
   does not support secure mechanism, the DHCPv6 server (for all of
   known DHCPv6 implementations) would just omit or disregard unknown
   options (secure options defined in this document) and still process
   the known options.  The reply message would be unsecured, of course.
   It is up to the local policy of the client whether to accept the
   messages.  If the client accepts the unsecured messages from the
   DHCPv6 server, the subsequent exchanges will be in the unsecured
   mode.

   In the scenario where a legacy client sends an unsecured message to a
   secure DHCPv6 enabled server, there are two possibilities depending
   on the server policy.  If the server's policy requires the
   authentication, an UnspecFail (value 1, [RFC3315]) error status code,
   SHOULD be returned.  In such case, the client cannot build up the
   connection with the server.  If the server has been configured to
   support unsecured clients, the server would fall back to the
   unsecured DHCPv6 mode, and reply unsecured messages toward the
   client.  The resources allocated for unsecured clients SHOULD be
   separated and restricted.

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:





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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_PK_PARAMETER       |         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 and
                  identify the algorithm with which the key is used
                  (e.g., RSA, DSA, or Diffie-Hellman).  The algorithm
                  is identified using the AlgorithmIdentifier structure
                  specified in section 4.1.1.2, [RFC5280].  The object
                  identifiers for the supported algorithms and the
                  methods for encoding the public key materials
                  (public key and parameters) are specified in
                  [RFC3279], [RFC4055], and [RFC4491].

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_CERT_PARAMETER     |         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. The
                  length of a certificate is various.



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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, including itself, 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     10 + 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.

   Timestamp      The current time of day (NTP-format timestamp
                  [RFC5905] in UTC (Coordinated Universal Time), a
                  64-bit unsigned fixed-point number, in seconds



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                  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 the Authentication Option.  It
   allows to be created after signature has been calculated and filled
   with the valid signature.  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.

5.4.  Status Codes

   o  AlgorithmNotSupported (TBD4): indicates that the DHCPv6 server
      does not support algorithms that sender used.

   o  AuthFailNotSupportLoF (TBD5): indicates that the DHCPv6 client
      fails authentication check and the DHCPv6 server does not support
      the leaf of faith mode

   o  AuthFailSupportLoF (TBD6): indicates that the DHCPv6 client fails
      authentication check.  Although the DHCPv6 server does support the
      leaf of faith, its list that stores public keys or unverifiable
      certificates in the leap of faith mode currently exceeds.

   o  TimestampFail (TBD7): indicates the message from DHCPv6 client
      fails the timstamp check.




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   o  SignatureFail (TBD8): indicates the message from DHCPv6 client
      fails the signature check.

6.  Processing Rules and Behaviors

   This section only covers the scenario where both DHCPv6 client and
   DHCPv6 server are secure enabled.

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 Public Key or a Certificate option,
   which MUST be constructed as explained in Section 5.1 or Section 5.2.

   A Secure DHCPv6 message, except for Relay-forward and Relay-reply
   messages, MUST contain one and only one Signature option, which MUST
   be constructed as explained in Section 5.3.  It protects the message
   header and all DHCPv6 options except for 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
   additional Public Key or Certificate option or Signature Option,
   aside from those present in the innermost encapsulated message from
   the client or server.

   If the sender is a DHCPv6 client, in the failure cases, it 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:

   o  Upon receiving a AlgorithmNotSupported error status code, the
      client MAY resend the message protected with the mandatory
      algorithms.

   o  Upon receiving an AuthFailNotSupportLoF error status code, the
      client is not able to build up the secure communication with the



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      recipient.  The client MAY switch to other certificate or public
      key if it has.  But it SHOULD NOT retry with the same certificate/
      public-key.  It MAY retry with the same certificate/public-key
      following normal retransmission routines defined in [RFC3315].

   o  Upon receiving an AuthFailSupportLoF error status code, the client
      is not able to build up the secure communication with the
      recipient.  The client MAY switch to other certificate or public
      key if it has.  The client MAY retry with the same certificate/
      public-key following normal retransmission routines defined in
      [RFC3315].

   o  Upon receiving a TimestampFail error status code, the client MAY
      fall back to unsecured mode.

   o  Upon receiving a SignatureFail error status code, the client MAY
      resend the message following normal retransmission routines
      defined in [RFC3315].

6.2.  Processing Rules of Recipient

   The recipient of a Secure DHCPv6 message could be a DHCPv6 server or
   a DHCPv6 client.  In the failure cases, both DHCPv6 server and client
   SHOULD NOT process received message, and the server SHOULD reply a
   correspondent error status code, while the client does nothing.  The
   specific behavior depends on the configured local policy.

   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 multiple
   Signature option is presented, or both the Public Key and Certificate
   options are absent, or both the Public Key and Certificate option are
   presented.  In such failure, the DHCPv6 server SHOULD reply an
   UnspecFail (value 1, [RFC3315]) error status code.  If all three
   options are absent, the sender MAY be legacy node or in unsecured
   mode, then, the recipient MAY fall back to the unsecured DHCPv6 mode
   if its local policy allows.

   The recipient SHOULD first check the support of algorithms that
   sender used.  If all algorithms are supported, the recipient then
   checks the authority of this sender.  If not, the message is dropped.
   In such failure, the DHCPv6 server SHOULD reply a
   AlgorithmNotSupported error status code, defined in Section 5.4, back
   to the client.

   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



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   verified certificate in order to avoid repeated verification
   procedure in the future.  A sender certificate that finds a match in
   the local trust certificate list is 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 matching 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 authentication 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 (LoF) that the sender is trustworthy.  If no evidence to the
   contrary surfaces, the recipient can then validate the sender as
   trustworthy for subsequent message exchanges.  In opposite, once the
   recipient has determined that it is being attacked, it can either
   forget that key, or remember that key in a blacklist and drop further
   packets associated with that key.

   If recipient does not support the leap of faith mode, the message
   that fails authentication check MUST be dropped.  In such failure,
   the DHCPv6 server SHOULD reply an AuthFailNotSupportLoF error status
   code, defined in Section 5.4, back to the client.

   On the recipient that supports the leap of faith mode, the number of
   cached public keys or unverifiable certificates MAY be limited in
   order to protect against resource exhaustion attacks.  If the
   recipient's list that stores public keys or unverifiable certificates
   in the leap of faith mode exceeds, the message that fails
   authentication check MUST be dropped.  In such failure, the DHCPv6
   server SHOULD reply an AuthFailNotSupportLoF error status code,
   defined in Section 5.4, back to the client.  The resource releasing
   policy against exceeding situations is out of scope.  Giving the
   complexity, the key rollover mechanism is out of scope of this
   document.

   At this point, the recipient has either recognized the authentication
   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 (see details in Section 6.4).  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.



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   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
   unsecured messages.  In the case the recipient is DHCPv6 server, the
   DHCPv6 server SHOULD reply a SignatureFail error status code, defined
   in Section 5.4, for the signature verification failure, or a
   TimestampFail error status code, defined in Section 5.4, for the
   timestamp check failure, back to the client.

   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 invalid.  The message MUST 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, by definition in
   this document, relay agents SHOULD NOT add any secure DHCPv6 options.

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 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.



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   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 timestamp in the last received and accepted DHCPv6 message.
      This is called TSlast.

   A 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

      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.

      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



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   entries.  The specific policy as to which entries are preferred over
   others is left as an implementation decision.

7.  Deployment Consideration

   This document defines two levels of authentication: full
   authentication based on certificate or pre-shared key verification
   and weaker authentication based on leap-of-faith (LoF).  As a
   mechanism, both levels can be applied on servers and clients.
   Depending on the details of expected threats and other constraints,
   some cases may have limited applicability.  This section discusses
   such details.

7.1.  Authentication on a client

   For clients, DHCP authentication generally means authenticating the
   server (the sender of DHCP messages) and verifying message integrity.

   This is satisfied with full authentication.  Due to the configuration
   overhead, however, full authentication may not always be feasible.
   It would still be viable in a controlled environment with skilled
   staff, such as a corporate intranet.

   If LoF is used, message integrity is provided but there is a chance
   for the client to incorrectly trust a malicious server at the
   beginning of the first session with the server (and therefore keep
   trusting it thereafter).  But LoF guarantees the subsequent messages
   are sent by the same server that sent the public key, and therefore
   narrows the attack scope.  This may make sense if the network can be
   reasonably considered secure and requesting pre-configuration is
   deemed to be infeasible.  A small home network would be an example of
   such cases.

   For environments that are neither controlled nor really trustworthy,
   such as a network cafe, full authentication wouldn't be feasible due
   to configuration overhead, while pure LoF, i.e. silently trusting the
   server at the first time, would be too insecure.  But some
   middleground might be justified, such as requiring human intervention
   at the point of LoF.

7.2.  Authentication on a server

   As for authentication on a server, there are several different
   scenarios to consider, each of which has different applicability
   issues.

   A server may have to selectively serve a specific client or deny
   specific clients depending on the identify of the client.  This will



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   require full authentication, since if the server allows LoF any
   malicious user can pretend to be a new legitimate client.  Also, the
   use of certification wouldn't be feasible in this case, since it's
   less likely for all such clients to have valid (and generally
   different) certificates.  So the applicable case may be limited, but
   a controlled environment with skilled staff and a specifically
   expected set of clients such as a corporate intranet may still find
   it useful and viable.

   A server can prevent an attack on the DHCP session with an existing
   client from a malicious client, e.g., by sending a bogus Release
   message: the server would remember the original client's public key
   at the beginning of the DHCP session and authenticate subsequent
   messages (and their sender).  Neither full authentication nor LoF is
   needed for this purpose, since the server does not have to trust the
   public key itself.  So this can be generally used for any usage of
   DHCP.

   A server can prevent an attack by a malicious client that pretends to
   be a valid past client and tries to establish a new DHCP session
   (whether this is a real security threat may be a subject of debate,
   but this is probably at least annoying).  This is similar to the
   first scenario, but full authentication may not necessarily be
   required; since the purpose is to confirm a returning client has the
   same identify as a valid past client, the server only has to remember
   the client's public key at the first time.  So LoF can be used at the
   risk of allowing a malicious client to mount this attack before the
   initial session with a valid client.  An uncontrolled, but reasonably
   reliable network like a home network may use this defense with LoF.

8.  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 discard 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.



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   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.

   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, how the two communicating 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.

9.  IANA Considerations

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



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

             Name        |  Value  |  RFCs
      -------------------+---------+--------------
            SHA-1        |   0x01  | this document
            SHA-256      |   0x02  | this document
            SHA-512      |   0x03  | this document

   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:

             Name        |  Value  |  RFCs
      -------------------+---------+--------------
       RSASSA-PKCS1-v1_5 |   0x01  | 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:










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         Code  |           Name        |   Reference
      ---------+-----------------------+--------------
         TBD4  | AlgorithmNotSupported | this document
         TBD5  | AuthFailNotSupportLoF | this document
         TBD6  |   AuthFailSupportLoF  | this document
         TBD7  |     TimestampFail     | this document
         TBD8  |     SignatureFail     | this document

10.  Acknowledgments

   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, Qi Sun, Suresh Krishnan,
   Tatuya Jinmei and other members of the IETF DHC working groups for
   their valuable comments.

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

11.  Change log [RFC Editor: Please remove]

   draft-ietf-dhc-sedhcpv6-03: addressed comments from WGLC.  Added a
   new section "Deployment Consideration".  Corrected the Public Key
   Field in the Public Key Option.  Added considation for large DHCPv6
   message transmission.  Added TimestampFail error code.  Refined the
   retransmission rules. 2014-06-18.

   draft-ietf-dhc-sedhcpv6-02: addressed comments (applicability
   statement, redesign the error codes and their logic) from IETF89 DHC
   WG meeting and volunteer reviewers. 2014-04-14.

   draft-ietf-dhc-sedhcpv6-01: addressed comments from IETF88 DHC WG
   meeting.  Moved Dacheng Zhang from acknowledgement to be co-author.
   2014-02-14.

   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



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   the suggestion from IESG making a general public key based mechanism.
   2013-06-29.

12.  References

12.1.  Normative References

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

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, December 1998.

   [RFC3279]  Bassham, L., Polk, W., and R. Housley, "Algorithms and
              Identifiers for the Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 3279, April 2002.

   [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.

   [RFC4055]  Schaad, J., Kaliski, B., and R. Housley, "Additional
              Algorithms and Identifiers for RSA Cryptography for use in
              the Internet X.509 Public Key Infrastructure Certificate
              and Certificate Revocation List (CRL) Profile", RFC 4055,
              June 2005.

   [RFC4443]  Conta, A., Deering, S., and M. Gupta, "Internet Control
              Message Protocol (ICMPv6) for the Internet Protocol
              Version 6 (IPv6) Specification", RFC 4443, March 2006.

   [RFC4491]  Leontiev, S. and D. Shefanovski, "Using the GOST R
              34.10-94, GOST R 34.10-2001, and GOST R 34.11-94
              Algorithms with the Internet X.509 Public Key
              Infrastructure Certificate and CRL Profile", RFC 4491, May
              2006.

   [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.





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

12.2.  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.

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










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   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


   Tatuya Jinmei
   WIDE Project
   Japan

   Email: jinmei@wide.ad.jp





































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