[Docs] [txt|pdf] [Tracker] [WG] [Email] [Nits]

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

DHC Working Group                                          Sheng Jiang
Internet Draft                            Huawei Technologies Co., Ltd
Intended status: Proposed Standard                           Sean Shen
Update: RFC3315                                                  CNNIC
Expires: December 31, 2013                               June 29, 2013

                     Secure DHCPv6 with Public Key
                    draft-jiang-dhc-sedhcpv6-00.txt


Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups. Note that other
   groups may also distribute working documents as Internet-Drafts.

   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."

   The list of current Internet-Drafts can be accessed at
        http://www.ietf.org/ietf/1id-abstracts.txt

   The list of Internet-Draft Shadow Directories can be accessed at
        http://www.ietf.org/shadow.html

   This Internet-Draft will expire on December 31, 2013.



Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors. All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document. Please review these documents
   carefully, as they describe your rights and restrictions with respect
   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.





Jiang & Shen          Expires December 31, 2013               [Page 1]


Internet-Draft       draft-jiang-dhc-sedhcpv6-00             June 2013



Abstract

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



Table of Contents

   1. Introduction ................................................ 3
   2. 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. Key/Certificate Option ................................. 6
      5.2. Signature Option ....................................... 6
   6. Processing Rules and Behaviors .............................. 8
      6.1. Processing Rules of Sender ............................. 8
      6.2. Processing Rules of Receiver ........................... 9
      6.3. Processing Rules of Relay Agent ....................... 10
      6.4. Timestamp Check ....................................... 11
   7. Security Considerations .................................... 12
   8. IANA Considerations ........................................ 13
   9. Acknowledgments ............................................ 14
   10. References ................................................ 14
      10.1. Normative References ................................. 14
      10.2. Informative References ............................... 14














Jiang & Shen          Expires December 31, 2013               [Page 2]


Internet-Draft       draft-jiang-dhc-sedhcpv6-00             June 2013



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:

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

      - The integrity of DHCPv6 messages can be checked by the receiver
        of the message.

   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. Terminology

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

3. Security Overview of DHCPv6

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

   a)   The basic DHCPv6 specifications can optionally authenticate the
      origin of messages and validate the integrity of messages using an
      authentication option with a symmetric key pair. [RFC3315] relies
      on pre-established secret keys. For any kind of meaningful
      security, each DHCPv6 client would need to be configured with its
      own secret key; [RFC3315] provides no mechanism for doing this.


Jiang & Shen          Expires December 31, 2013               [Page 3]


Internet-Draft       draft-jiang-dhc-sedhcpv6-00             June 2013

      For the key of the hash function, there are two key management
      mechanisms. Firstly, the key management is out of band, usually
      manual, i.e., operators set up key database for both server and
      client before running DHCPv6. Usually multiple keys are deployed
      one a time and key id is used to specify which key is used.

      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.

      Comparing to this, the public/private key pair security mechanism
      only require a key pair on the sender. The key management
      mechanism is very simple.

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

4. Secure DHCPv6 Overview

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

   This document introduces a Secure DHCPv6 mechanism that uses the
   public/private key pair to secure the DHCPv6 protocol. It assumes:
   a) the secured DHCPv6 message sender already has a public/private key
   pair; b) the receiver has already been have the public key of the
   sender, which may be pre-configured or recorded from previous
   communications, or the public key of CA (Certificate Authority),
   which issues the sender's certificate and is trusted by the receiver.

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

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


Jiang & Shen          Expires December 31, 2013               [Page 4]


Internet-Draft       draft-jiang-dhc-sedhcpv6-00             June 2013

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

4.1. New Components

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

      - A public/private key pair has been generated by a node itself.
        The node may request a CA to sign its public key to get a
        trustable certificate, which contains the original public key.
        Two new DHCPv6 option are defined to carry the public key or
        the certificate of the sender.

      - Signatures signed by private key protect the integrity of the
        DHCPv6 messages and authenticate the identity of the sender.

      - Timestamp, a value that indicates the relative time in second.

4.2. Support for algorithm agility

   Hash functions are the fundamental security mechanism. "...they have
   two security properties: to be one way and collision free." "The
   recent attacks have demonstrated that one of those security
   properties is not true." [RFC4270] It is theoretically possible to
   perform collision attacks against the "collision-free" property.

   Following the approach recommended by [RFC4270] and [NewHash], recent
   analysis shows none of these attacks are currently possible,
   according to [RFC6273]. "The broken security property will not affect
   the overall security of many specific Internet protocols, the
   conservative security approach is to change hash algorithms."
   [RFC4270]

   However, these attacks indicate the possibility of future real-world
   attacks. Therefore, we have to take into account that attacks will
   improved in the future, and provide a support for multiple hash
   algorithms. Our mechanism, in this document, supports not only hash
   algorithm agility but also signature algorithm agility.

   The support for algorithm agility in this document is mainly a
   unilateral notification model from a sender to a receiver. If the
   receiver cannot support the algorithm provided by the sender, it
   takes the risk itself. Senders in a same network do not have to
   upgrade to a new algorithm simultaneously.




Jiang & Shen          Expires December 31, 2013               [Page 5]


Internet-Draft       draft-jiang-dhc-sedhcpv6-00             June 2013

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. Key/Certificate Option

   The Key/Certificate option carries the public key or certificate 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 Key/Certificate    |         option-len            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |    K/C Flag   |                                               |
       +-+-+-+-+-+-+-+-+                                               .
       .        Public Key or Certificate (variable length)            .
       .                                                               .
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       option-code     OPTION_KC_PARAMETER (TBA1).

       option-len      1+ length of public key/certificate in octets.

       K/C Flag        Flag to indicate whether the value is a public
                       key or certificate. 00x for public key; FFx for
                       certificate. Other values may be extended in the
                       future.

       Public key      A variable-length field containing public key or
                       certificate.

5.2. 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 Signature option itself and 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              |


Jiang & Shen          Expires December 31, 2013               [Page 6]


Internet-Draft       draft-jiang-dhc-sedhcpv6-00             June 2013

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

       option-code     OPTION_SIGNATURE (TBA2).

       option-len      12 + Length of Signature field and Padding field
                       in octets.

       HA-id          Hash Algorithm id. The hash algorithm is used
                       for computing the signature result. This design
                       is adopted in order to provide hash algorithm
                       agility. The value is from the Hash Algorithm
                       for Secure DHCPv6 registry in IANA. The initial
                       values are assigned for SHA-1 is 0x0001.

       SA-id          Signature Algorithm id. The signature algorithm
                       is used for computing the signature result. This
                       design is adopted in order to provide signature
                       algorithm agility. The value is from the
                       Signature Algorithm for Secure DHCPv6 registry
                       in IANA. The initial values are assigned for
                       RSASSA-PKCS1-v1_5 is 0x0001.

       Reserved        A 16-bit field reserved for future use. The
                       value MUST be initialized to zero by the sender,
                       and MUST be ignored by the receiver.

       Timestamp       The current time of day (NTP-format timestamp
                       [RFC5905], 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 128-bit Source IPv6 Address.

                       2. The 128-bit Destination IPv6 Address.


Jiang & Shen          Expires December 31, 2013               [Page 7]


Internet-Draft       draft-jiang-dhc-sedhcpv6-00             June 2013


                       3. The DHCPv6 message header.

                       4. All DHCPv6 options except for the Signature
                       option and the Authentication Option.

                       5. The content between the option-len field and
                       the signature field in this Signature option, in
                       the format described above.

       Padding        This variable-length field contains padding, as
                       many bits long as remain after the end of the
                       signature. This padding is only needed if the
                       length of signature is not a multiple of 8
                       bits.

   Note: a Relay-Reply message is constructed by a DHCPv6 server in
   segments. The server first constructs the server message for client,
   which includes a Signature Option that covers the server message. In
   the signed data, the destination address is the address of the
   client. It then constructs the Relay-Reply message by encapsulating
   the server message into a Relay Message Option. If there is
   additional option for relay, the server MUST include another
   Signature Option, which covers the entire Relay-Reply message. In the
   signed data, the destination address is the address of the target
   relay agent.

6. Processing Rules and Behaviors

6.1. Processing Rules of Sender

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

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

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

   A Secure DHCPv6 message MUST contain both the Key/Certificate option
   and the Signature option, except for Relay-forward and Relay-reply
   Messages.

   Senders SHOULD set the Timestamp field to the current time, according
   to their real time clocks.




Jiang & Shen          Expires December 31, 2013               [Page 8]


Internet-Draft       draft-jiang-dhc-sedhcpv6-00             June 2013

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

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

   The Signature option MUST be constructed as explained in Section 5.2.
   It protects the message header and the message payload and all DHCPv6
   options except for the Signature option itself and the Authentication
   Option.

6.2. Processing Rules of Receiver

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

   The receiver SHOULD first check the authority of this sender. If the
   sender uses public key in the Key/Certificate option, the receiver
   SHOULD trust it by finding a match public key from the local trust
   public key list, which is pre-configured or recorded from previous
   communications. If the sender uses certificate in the Key/Certificate
   option, the receiver SHOULD validation the sender's certificate
   following the rules defined in [RFC5280]. An implementation may then
   create a local trust certificate record, too. The receiver may choose
   to further process the message from an unauthorized sender so that a
   leap of faith may be built up.

   Then, the receiver MUST verify the Signature and check 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 computational expensive.

   The signature field verification MUST show that the signature has
   been calculated as specified in Section 5.2.

   Only the messages that get through both the signature verifications
   and timestamp check are accepted as secured DHCPv6 messages and


Jiang & Shen          Expires December 31, 2013               [Page 9]


Internet-Draft       draft-jiang-dhc-sedhcpv6-00             June 2013

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

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

       Minbits        The minimum acceptable key length for public
                       keys. An upper limit MAY also be set for the
                       amount of computation needed when verifying
                       packets that use these security associations.
                       The appropriate lengths SHOULD be set according
                       to the signature algorithm and also following
                       prudent cryptographic practice. For example,
                       minimum length 1024 and upper limit 2048 may be
                       used for RSA [RSA].

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

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

6.3. Processing Rules of Relay Agent

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

   In the client-relay-server scenario, the relay agent MAY verify the
   signature as a receiver before relaying the client message further,
   following verification procedure define in Section 6.2. In the case
   of failure, it MUST discard the DHCPv6 message. However, the
   verification procedure on relay agents does not save the load of the



Jiang & Shen          Expires December 31, 2013              [Page 10]


Internet-Draft       draft-jiang-dhc-sedhcpv6-00             June 2013

   DHCPv6 server. The server still MUST verify the signature by itself
   in order to prevent the attack between the relay agent and server.

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

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

6.4. Timestamp Check

   Receivers SHOULD be configured with an allowed timestamp Delta value,
   a "fuzz factor" for comparisons, and an allowed clock drift
   parameter.  The recommended default value for the allowed Delta is
   300 seconds (5 minutes); for fuzz factor 1 second; and for clock
   drift, 0.01 second.

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

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

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

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

   Receivers SHOULD then 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

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




Jiang & Shen          Expires December 31, 2013              [Page 11]


Internet-Draft       draft-jiang-dhc-sedhcpv6-00             June 2013

    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 SEND message:

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

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

       Moreover, if the above inequality holds and TSnew > TSlast, the
       receiver SHOULD update RDlast and TSlast. Otherwise, the receiver
       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
   receiver 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
   new unverified certificate, it can make a leap of faith. If the
   DHCPv6 server that used that public key/certificate is in fact
   legitimate, then all future communication with that DHCPv6 server can
   be protected by caching the public key. This does not provide
   complete security, but it limits the opportunity to mount an attack
   on a specific DHCPv6 client to the first time it communicates with a
   new DHCPv6 server.


Jiang & Shen          Expires December 31, 2013              [Page 12]


Internet-Draft       draft-jiang-dhc-sedhcpv6-00             June 2013

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

   [RFC6273] has analyzed possible threats to the hash algorithms used
   in SEND. Since the Secure DHCPv6 defined in this document uses the
   same hash algorithms in similar way to SEND, analysis results could
   be applied as well: current attacks on hash functions do not
   constitute any practical threat to the digital signatures used in the
   signature algorithm in the Secure DHCPv6.

   A window of vulnerability for replay attacks exists until the
   timestamp expires. Secure DHCPv6 nodes are protected against replay
   attacks as long as they cache the state created by the message
   containing the timestamp. The cached state allows the node to protect
   itself against replayed messages. However, once the node flushes the
   state for whatever reason, an attacker can re-create the state by
   replaying an old message while the timestamp is still valid.

   Attacks against time synchronization protocols such as NTP [RFC5905]
   may cause Secure DHCPv6 nodes to have an incorrect timestamp value.
   This can be used to launch replay attacks, even outside the normal
   window of vulnerability.  To protect against these attacks, it is
   recommended that SEND nodes keep independently maintained clocks or
   apply suitable security measures for the time synchronization
   protocols.

8. IANA Considerations

   This document defines two new DHCPv6 [RFC3315] options, which MUST be
   assigned Option Type values within the option numbering space for
   DHCPv6 messages:

       The Key/Certificate Parameter Option (TBA1), described in Section
       5.1.

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

   This document defines two new registries that have been created and
   are maintained by IANA. 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 name space are
   16-bit unsigned integers. The following initial values are assigned
   for Hash Algorithm for Secure DHCPv6 in this document:

             Name        |  Value  |  RFCs
      -------------------+---------+------------


Jiang & Shen          Expires December 31, 2013              [Page 13]


Internet-Draft       draft-jiang-dhc-sedhcpv6-00             June 2013

            Reserved     |  0x0000 | this document
            SHA-1        |  0x0001 | this document
            SHA-256      |  0x0002 | this document

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

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

9. Acknowledgments

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

10. References

10.1. Normative References

   [RFC3315] R. Droms, et al., "Dynamic Host Configure Protocol for
             IPv6", RFC 3315, July 2003.

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

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

10.2. Informative References

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

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

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

   [RFC6273] A. Kukec, S. Krishnan and S. Jiang "The Secure Neighbor
             Discovery (SEND) Hash Threat Analysis", RFC 6274, June
             2011.


Jiang & Shen          Expires December 31, 2013              [Page 14]


Internet-Draft       draft-jiang-dhc-sedhcpv6-00             June 2013

   [NewHash] S.Bellovin and E. Rescorla, "Deploying a New Hash
             Algorithm", November 2005.

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

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



   Author's Addresses

   Sheng Jiang
   Huawei Technologies Co., Ltd
   Q14, Huawei Campus
   No.156 Beiqing Road
   Hai-Dian District, Beijing  100095
   P.R. China
   EMail: jiangsheng@huawei.com

   Sean Shen
   CNNIC
   4, South 4th Street, Zhongguancun
   Beijing 100190
   P.R. China
   EMail: shenshuo@cnnic.cn























Jiang & Shen          Expires December 31, 2013              [Page 15]

Html markup produced by rfcmarkup 1.129b, available from https://tools.ietf.org/tools/rfcmarkup/