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Versions: (draft-jiang-dhc-secure-dhcpv6) 00 01 02 03 04 05 06 07

DHC Working Group                                          Sheng Jiang
Internet Draft                            Huawei Technologies Co., Ltd
Intended status: Standards Track                             Sean Shen
Update: RFC3315                                                  CNNIC
Expires: September 18, 2012                             March 12, 2012

                        Secure DHCPv6 Using CGAs
                  draft-ietf-dhc-secure-dhcpv6-06.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
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   This Internet-Draft will expire on September 18, 2012.



Copyright Notice

   Copyright (c) 2012 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
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   described in the Simplified BSD License.





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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 attack. This document analyzes
   the security issues of DHCPv6 and specifies a Secure DHCPv6 mechanism
   based on using CGAs.



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. CGA Parameter Option ................................... 6
      5.2. Signature Option ....................................... 6
      5.3. DUID-SA Type ........................................... 9
   6. Processing Rules and Behaviors .............................. 9
      6.1. Processing Rules of Sender ............................. 9
      6.2. Processing Rules of Receiver .......................... 10
      6.3. Processing Rules of Relay Agent ....................... 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
















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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 attack.

   This document analyzes the security issues of DHCPv6 in details. This
   document is aiming to provide mechanisms for improving the security
   of DHCPv6, thus the address of a DHCPv6 message sender, which can be
   a DHCPv6 server, a relay agent or a client, can be verified by a
   receiver. It improves communication security of DHCPv6 interaction.
   The security mechanisms specified in this document is mainly based on
   the Cryptographically Generated Addresses (CGA [RFC3972]).

   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 auto-configure
   relevant network parameters on clients through the DHCPv6 message
   exchanging mechanisms. In the basic DHCPv6 specifications [RFC3315],
   security of DHCPv6 message can be improved in a few aspects.

   a)   In the basic DHCPv6 specifications, the DHCPv6 server uses a
      "regular" IPv6 address for itself. It is possible for a malicious
      attacker to use a fake address to spoof or launch an attack. See
      Section 23, "Security Considerations" of [RFC3315] for more
      details.

      Furthermore, if DHCPv6 servers play the role of updating DNS and
      other directory services, attackers may spoof DHCPv6 servers to
      register incorrect information in those services.

      CGA-based security mechanism can provide source address ownership
      proofing, which prevents such attacks.

   b)   The basic DHCPv6 specifications achieve message origin
      authentication and message integrity via an authentication option


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      with a symmetric key pair. 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 once 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. Secondly, a
      DHCPv6 server sends a reconfigure key to the client in the initial
      exchange of DHCPv6 messages for future use, in this case security
      is not guaranteed because this key is transmitted in plaintext.

      Comparing to this, CGA-based security mechanism does not request
      any key management mechanisms.

   c)   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 may have
      better deploy ability.

4. Secure DHCPv6 Overview

   To solve the abovementioned security issues, we introduce CGAs into
   DHCPv6. CGAs are introduced in [RFC3972]. The usage of CGAs combining
   with associated signatures can verify the address ownership and
   protect messages "without a certification authority or any security
   infrastructure." [RFC3972]

   This documentation introduces a Secure DHCPv6 mechanism that uses
   CGAs to secure the DHCPv6 protocol. It assumes the secured DHCPv6
   message sender has already haven CGAs and their correspondent CGA
   parameters; and the receiver has already been given the CGAs of the
   sender.

   In this document, a CGA option with an address ownership proof
   mechanism and a signature option with a corresponding verification
   mechanism are introduced. A DHCPv6 message (from either a server, a
   relay agent or a client) with a CGA as source address, can carry the
   CGA Parameters data structure and a digital signature. The receiver
   of this DHCPv6 message, who has already known the CGA of the sender,
   can verify both the CGA and signature, then process the payload of
   the DHCPv6 message only if the validation is successful.

   With them, the receiver of a DHCPv6 message can verify the sender
   address of the DHCPv6 message, which improves communication security
   of DHCPv6 messages. The verification of data integrity and replay
   protections can also be achieved without the authentication option.

   The sender can be a DHCPv6 server, a relay agent or a client. So, the
   end-to-end security protection can be from DHCPv6 servers to relay


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   agents or clients, or from clients to relay agent or DHCPv6 servers.
   Relay agents MAY add its own Secure DHCPv6 options, too.

4.1. New Components

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

      - CGAs are used to make sure that the sender of a DHCPv6 message
        is the "owner" of the claimed address. A public-private key
        pair has been generated by a node itself before it can claim an
        address. A new DHCPv6 option, the CGA Parameter Option, is used
        to carry the public key and associated parameters.

      - Public key signatures protect the integrity of the DHCPv6
        messages and authenticate the identity of their sender.

      - Server Address type of DUID is used to carry server's source
        address in the relay scenarios. The receiver gets the server's
        source CGA address for CGA verification.

4.2. Support for algorithm agility

   Hash functions are the fundamental of security mechanisms, including
   CGAs in this document. "...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 attack Attacks against
   the "collision-free" property.

   Following the approach recommended by [RFC4270] and [NewHash], recent
   analysis shows none of these attacks are currently doable [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 future attacks
   will be improved and provide a support for multiple hash algorithms.
   Our mechanisms, in this document, support not only hash algorithm
   agility but also signature algorithm agility.

   The support for hash agility within CGAs has been defined in
   [RFC4982]. The usage of CGAs in this document SHOULD also obey
   [RFC4982], too.

   The support for algorithm agility in this document is mainly
   unilateral notification model from a sender to a receiver. If the
   receiver cannot support the algorithm provided by the sender, it



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   takes the risk itself. Senders in a same network do not have to
   upgrade to a new algorithm simultaneously.

5. Extensions for Secure DHCPv6

   This section extends DHCPv6. Two new options and a new DUID type have
   been defined. The new options MUST be supported in the Secure DHCPv6
   message exchanging. The new DUID type MUST be supported in the relay
   scenarios.

5.1. CGA Parameter Option

   The CGA option allows the verification of the sender's CGAs. The
   format of the CGA 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_CGA_PARAMETER    |         option-len              |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       .                                                               .
       .                 CGA Parameters (variable length)              .
       .                                                               .
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       option-code     OPTION_CGA_PARAMETER (TBA1).

       option-len      Length of CGA Parameters in octets.

       CGA Parameters   A variable-length field containing the CGA
                       Parameters data structure described in Section 4
                       of [RFC3972]. This specification requires that
                       the public key found from the CGA Parameters
                       field in the CGA option MUST be that referred by
                       the Key Hash field in the Signature option.
                       Packets received with two different keys MUST be
                       silently discarded.

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 all the DHCPv6 header and
   options, particularly including the CGA option, except for the
   Signature option and the Authentication Option. The format of the
   Signature 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_SIGNATURE        |         option-len              |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |           HA-id             |              SA-id              |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |          HA-id-KH           |             Reserved            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                     Timestamp (64-bit)                        |
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       |                     Key Hash (128-bit)                        |
       |                                                               |
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       .                    Signature (variable length)                .
       .                                                               .
       .                                                     +-+-+-+-+-+
       |                                                     | Padding |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       option-code     OPTION_SIGNATURE (TBA2).

       option-len      32 + 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.

       SA-id          Signature Algorithm id. The signature algorithm
                       is used for computing the signature result. This
                       design is adopted in order to provide hash
                       algorithm agility.

       HA-id-KH        Hash Algorithm id for Key Hash. Hash algorithm
                       used for producing the Key Hash field in the
                       Signature option. This design is adopted in
                       order to provide hash algorithm agility.

       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.



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       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.

       Key Hash        A 128-bit field containing the most significant
                       (leftmost) 128 bits of the hash value of the
                       public key used for constructing the signature.
                       The hash algorithm is indicated in the HA-id-KH
                       field. The field is taken over the presentation
                       used in the Public Key field of the CGA
                       Parameters data structure carried in the CGA
                       option. Its purpose is to associate the
                       signature to a particular key known by the
                       receiver. Such a key can either be stored in the
                       certificate cache of the receiver or be received
                       in the CGA option in the same message.

       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 CGA Message Type tag value for
                       Secure DHCPv6, 0x81be a1eb 0021 ce7e caa9 4090
                       0665 d2e0 02c2.

                       2. The 128-bit Source IPv6 Address.

                       3. The 128-bit Destination IPv6 Address.

                       4. The DHCPv6 message header.

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

                       6. 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.





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5.3. DUID-SA Type

   Server Address Type DUID (DUID-SA) allows IP address of DHCPv6
   servers can be carried in DHCPv6 message payload.

   The following diagram illustrates the format of a DUID-SA:

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             TBA3            |                                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                                 |
   |                                                               |
   |                     Server Address (128-bit)                  |
   |                                                               |
   |                             +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       Type-code       DUID-SA Type (TBA3)

       Server Address   The 128-bit IPv6 address of the DHCPv6 server.

   The Server Address field of DUID-SA, which is the IPv6 address of the
   DHCPv6 server, MUST be a CGA.

   In the server-relay-client scenarios, a DHCPv6 server knows a client
   is behind relay(s) if it receives a Relay-forward DHCPv6 message.
   Then it will reply a Relay-reply message with the server's source CGA
   address being carried in the Server Address Type DUID, which is in
   the payload. In this way, the receiver, a DHCPv6 client can get the
   server's source CGA address for CGA verification.

   All the payloads, including DUID-SA, are protected by signature
   option by the definition of section 5.1 and 5.2.

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 the following information in order to create
   Secure DHCPv6 messages:

       CGA parameters   Any information required to construct CGAs, as
                       described in [RFC3972].





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       Keypair        A public-private key pair. The public key used
                       for constructing the signature MUST be the same
                       in CGA parameters.

       CGA flag        A flag that indicates whether CGA is used or
                       not.

   To support Secure DHCPv6, the Secure DHCPv6 enabled sender MUST
   construct the DHCPv6 message following the rules defined
   in [RFC3315]. The sender MUST use a CGA, which be constructed as
   specified in Section 4 of [RFC3972], as the source address, unless
   they are sent with the unspecified source address.

   A Secure DHCPv6 message MUST contains both the CGA option and the
   Signature option.

   The CGA option is constructed according to the rules presented in
   Section 5.1 and in [RFC3972]. The public key in the field is the one
   associated with the CGA, which is also the source address in the
   message header.

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

   When constructing a Relay-reply message, a DHCPv6 server MUST include
   an OPTION_SERVERID [RFC3315] and put its CGA in the Server Address
   field of the DUID in the OPTION_SERVERID. By applying this rule, the
   CGA of the DHCPv6 server will not be lost when the Relay-reply
   message passes relay agents so that the client can verify CGA address
   and signature.

6.2. Processing Rules of Receiver

   By receiving a DHCPv6 message, a Secure DHCPv6 enabled receiver MUST
   discard the DHCPv6 message if either the CGA option or the Signature
   option absents.

   The receiving node MUST verify the source CGA address of the DHCPv6
   message by using the public key of the DHCPv6 message sender, CGA
   Parameters and the algorithm described in Section 5 of [RFC3972]. The
   inputs to the algorithm are the source address, as used in IP header,
   and the CGA Parameters field. In the relay scenarios, a DHCPv6 server
   obtains the CGA of a client from the peer address field in the Relay-
   forward message. A DHCPv6 client obtains the CGA of a server from the
   Server Address field of the DUID in the OPTION_SERVERID.

   If the CGA verification is successful, the recipient proceeds with a
   more time-consuming cryptographic check of the signature. Note that


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   even if the CGA verification succeeds, no claims about the validity
   of the use can be made until the signature has been checked.

   The receiving node MUST verify the Signature option as follows: the
   Key Hash field MUST indicate the use of a known public key, the one
   learned from a preceding CGA option in the same message. 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 CGA and signature
   verifications 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 all the above tests MUST be
   discarded.

   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 used in the generation of CGAs. 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].

6.3. Processing Rules of Relay Agent

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

   A relay agent MAY verify the CGA and signature as a receiver before
   relay the DHCPv6 message further, following verification procedure
   define in Section 6.2. In the case of failure, it MUST discard the
   DHCPv6 message.

   In the relay scenarios, because relay agent restructures the DHCPv6
   messages, a downstream receiver would not find the sender's source
   CGA address in the DHCPv6 message header.

   In the client-relay-server scenarios, "The relay agent copies the
   source address from the IP datagram in which the message was received
   from the client into the peer-address field in the Relay-forward
   message" [RFC3315]. Therefore, the CGA of a client will not be lost
   during the relay processing from the client to the server. The
   receiver, a DHCPv6 server, can find the sender's source CGA address
   in the peer-address field for CGA verification.


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   During the relay processing from the server to the client, when the
   relay agent constructs the Relay-reply message the server's IP
   address is replaced by the relay's IP address. In order to make the
   CGA of the DHCPv6 server reach the client, DUID-SA, described in
   Section 5.3, MUST be used. A relay will not change the
   OPTION_SERVERID when processing Relay-reply message from a DHCPv6
   server, so that the CGA of the DHCPv6 server will not be lost when
   the Relay-reply message passes the Relay Agent.

   Relay agents MAY also added its own CGA option and signature option
   in the Relay-forward or Relay-reply messages. By receiving such
   messages, the downstream receiver MUST verify CGA and signature from
   the relay agent, and CGA and signature from the original sender.

7. Security Considerations

   This document provides new security features to the DHCPv6 protocol.

   Using CGA as source addresses of DHCPv6 servers, relays or, also in
   DHCPv6 message exchanging provides the source address ownership
   verification and data integrity protection.

   The Secure DHCPv6 mechanism is based on the precondition that the
   receiver has known the CGA of senders. For example, to prevent DHCPv6
   server spoofing, the clients should be pre-notified the DHCPv6 server
   CGA. The clients may decline the DHCPv6 messages from other servers,
   which may be fake servers. The pre-notification operation also needs
   to be protected, which is out of scope.

   DHCPv6 nodes without CGAs or the DHCPv6 messages that use unspecific
   addresses cannot be protected.

   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. One
   simple solution may be that Secure DHCPv6 is mandated on all servers,
   relay agents and clients on a certain link.

   As stated in CGA definition [RFC3972], link-local CGAs are more
   vulnerable because the same prefix is used by all IPv6 nodes.
   Therefore, when link-local CGAs are used by the DHCPv6 clients, it is
   recommended to use a slightly higher Sec value, for example Sec=1 for
   now. When higher Sec values are used, the relative advantage of
   attacking link-local addresses becomes insignificant.

   Impacts of collision attacks on current uses of CGAs are analyzed in
   [RFC4982]. The basic idea behind collision attacks, as described in
   Section 4 of [RFC4270], is on the non-repudiation feature of hash
   algorithms. However, CGAs do not provide non-repudiation features.
   Therefore, as [RFC4982] points out CGA-based protocols, including


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   Secure DHCPv6 defined in this document, are not affected by collision
   attacks on hash functions.

   [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 like SEND (except that Secure
   DHCPv6 has not used PKIX Certificate), 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. Attacks on CGAs, as described in
   [RFC4982], will compromise the security of Secure DHCPv6 and they
   need to be addressed by encoding the hash algorithm information into
   the CGA as specified in [RFC4982].

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 CGA Parameter Option (TBA1), described in Section 5.1.

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

   This document defines a new DHCPv6 DUID, which MUST be assigned DUID
   Type values within the DHCPv6 DUID Type numbering space:

      The DUID-SA (TBA3), described in Section 5.3.

   This document defines three 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 id (HA-id). The values in this name space are 16-bit
   unsigned integers. The following initial values are assigned for HA-
   id in this document:

             Name        |  Value  |  RFCs
      -------------------+---------+------------
            SHA-1        |  0x0000 | this document

   Signature Algorithm id (SA-id). The values in this name space are 16-
   bit unsigned integers. The following initial values are assigned for
   SA-id in this document:

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


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   Hash Algorithm id for Key Hash (HA-id-KH). The values in this name
   space are 16-bit unsigned integers. The following initial values are
   assigned for HA-id-KH in this document:

             Name        |  Value  |  RFCs
      -------------------+---------+------------
            SHA-1        |  0x0000 | this document

   This document defines a new 128-bit value under the CGA Message Type
   [RFC3972] namespace, 0x81be a1eb 0021 ce7e caa9 4090 0665 d2e0 02c2.
   (The tag value has been generated randomly by the editor of this
   specification. It may replaced by any IANA-allocated value when the
   specification is published.)

9. Acknowledgments

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

10. References

10.1. Normative References

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

   [RFC3972] T. Aura, "Cryptographically Generated Address", RFC3972,
             March 2005.

   [RFC4982] M. Bagnulo, J. Arkko, "Support for Multiple Hash Algorithms
             in Cryptographically Generated Addresses (CGAs)", RFC4982,
             July 2007.

   [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.



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

   [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



















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