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Versions: 00 01

CGA & Send maintenance                                        T. Cheneau
Internet-Draft                                            M. Maknavicius
Expires: December 7, 2009                                           TMSP
                                                                 S. Sean
                                                                  Huawei
                                                           M. Vanderveen
                                                                Qualcomm
                                                            June 5, 2009


Support for Multiple Signature Algorithms in Cryptographically Generated
                            Addresses (CGAs)
                    draft-cheneau-cga-pk-agility-01

Status of this Memo

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Abstract

   This document defines an extension field for the CGA Parameters data
   structure specified in RFC 3972.  This extension field carries a
   Public Key that is used in Cryptographically Generated Address (CGA)
   generation.  This extension enables protocols using CGAs, such as
   SEND, to use multiple Public Key signing algorithms and/or multiple
   Public Keys.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Public Key extension . . . . . . . . . . . . . . . . . . . . .  4
     2.1.  Public Key extension format  . . . . . . . . . . . . . . .  4
   3.  CGA Generation Process . . . . . . . . . . . . . . . . . . . .  6
   4.  Security Consideration . . . . . . . . . . . . . . . . . . . .  9
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 10
   6.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     6.1.  Normative References . . . . . . . . . . . . . . . . . . . 11
     6.2.  Informative References . . . . . . . . . . . . . . . . . . 11
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13





























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1.  Introduction

   Cryptographically Generated Addresses (CGA) [RFC3972] have been
   designed to provide a binding of an internet address (IPv6) to a
   public key.  A node who claims to own a particular IPv6 address, can
   prove so in the messages (e.g.  ICMP) it sends by using a digital
   signature for authentication and integrity protection.  Since the
   IPv6 address was generated from the public key, verification of the
   respective signature is tantamount to verification of ownership of
   the claimed IPv6 address.

   CGAs [RFC3972] were defined to only use RSA as the associated
   signature algorithm.  Only one RSA public key is associated with a
   CGA and this public key is carried in the Public Key field of the CGA
   Parameters data structure.

   Due to the expected variations in cryptographic ability of IPv6
   nodes, support for signature algorithm agility in CGA is desired.
   However, since the CGA specification [RFC3972] states that SEND
   "SHOULD" use an RSA public/private key pair, backward compatibility
   is preserved herein.

   A logical place for extending the CGA Parameters data structure to
   include other types of public keys is its "extension fields".  Some
   guidance on the format of these extensions is provided in [RFC4581].
   One type of CGA Parameters data structure extension is defined in
   Section 2 and this type of extension is able to carry public keys, in
   addition to the RSA public key defined in the Public Key field of CGA
   Parameters data structure.

   These extensions allow new functionnalities on CGA based protocols,
   such as the Signature Algorithm Agility in SEND
   [cheneau-send-sig-agility].


















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2.  Public Key extension

   This section describes an extension field that conforms to the
   guidelines of [RFC4581].

   This extension allows a CGA Parameters data structure to carry public
   keys in addition to the key in the Public Key field.  This approach
   paves the way for one CGA to possibly be associated with multiple
   public keys.

   This extension allows a node to select a Public Key value that is
   different from the one in the Public Key field of the CGA Parameters
   data structure option.  This Public Key is placed in an extension
   embedded in the Extension field of the CGA Parameters data structure,
   described in [RFC3972].

2.1.  Public Key extension format

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Extension Type        |      Extension Length         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                       Public Key                              ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Figure 1: Public Key extension format

   Extension Type

      TBA. (16-bit unsigned integer.  See Section 5.)

   Extension Length

      The length of the Public Key field to follow, in octets. 16-bit
      unsigned integer.

   Public Key

      This is a variable-length field containing the public key of the
      sender.  The public key MUST be formatted as a DER-encoded
      [ITU.X690.2002] ASN.1 structure of the type SubjectPublicKeyInfo,
      defined in the Internet X.509 certificate profile [RFC5280].  When
      RSA is used, the algorithm identifier MUST be rsaEncryption, which
      is 1.2.840.113549.1.1.1, and the RSA public key MUST be formatted
      by using the RSAPublicKey type as specified in Section 2.3.1 of



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      [RFC3279].  The RSA key length SHOULD be at least 384 bits.

      When ECC is used, the algorithm identifier MUST be of type id-
      ecPublicKey (OID 1.2.840.10045.2.1), as defined in [RFC5480].  ECC
      public key encoding is specified in this reference.  Note that the
      ECC key lengths are determined by the ECParameters field named
      namedCurves (curves implying key length).












































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3.  CGA Generation Process

   When a node supports two or more types of signing algorithms, and is
   able to generate two or more corresponding public keys, then it can
   derive a single CGA using all these keys.  The derivation is done
   exactly as in [RFC3972]; one key is placed in the CGA Parameters data
   structure "Public Key" field while the rest of the keys are placed in
   separate extension fields.  This is illustrated in Figure 2.

   It should be noted that the type of the public key (RSA, ECC, etc.)
   is already encoded into the "Public Key" field itself, and thus there
   is no need to identify the public key type separately.  This is due
   to the fact that the "Public Key" field, according to [RFC3972] is a
   DER-encoded ASN.1 structure of the type "SubjectPublicKeyInfo", and
   therefore includes a subfield called "AlgorithmIdentifier".




































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     List of keys             CGA Parameters data structure

                          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                          |                             |
                          +         Modifier            |
                          |                             |
                          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                          |                             |
                          +      Subnet Prefix          +
                          |                             |
                          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                          |Col Count|                   |
   +-+-+-+-+-+-+-+-+      +-+-+-+-+-+
   |               |      |        Public Key           |
   ~  Public Key 1 ~ ->   ~                             ~
   |               |      |     (variable length)       |
   +-+-+-+-+-+-+-+-+      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   +-+-+-+-+-+-+-+-+      |         Extension           |
   |               |      ~       Public Key 2          ~
   ~  Public Key 2 ~ ->   |     (variable length)       |
   |               |      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   +-+-+-+-+-+-+-+-+      |                             |
                          ~           ...               ~
                          |                             |
   +-+-+-+-+-+-+-+-+      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |               |      |         Extension           |
   ~  Public Key N ~ ->   ~       Public Key N          ~
   |               |      |     (variable length)       |
   +-+-+-+-+-+-+-+-+      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                          |      Extension Fields       |
                          ~                             ~
                          | (optional, variable length) |
                          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


           Figure 2: CGA Parameters structure with multiple keys

   Note that an implementation should choose the number of simultaneous
   Public Key Extension fields used so as the total length of the
   extension fields does not exceed a threshold that requires
   fragmentation support at the SEND or other upper-layer protocol.

   Support for RSA Public Keys and signature algorithm is only
   RECOMMENDED for backward compatibility.  This specification does not
   mandate support for any particular public key signature algorithm.
   Therefore, nodes can be configured to choose/support only a single
   additional signature algorithm besides RSA.  However, a node is also
   free to not support RSA and still claim compatibility with this



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   specification.

   Since [RFC3972] mandates the use of RSA keys in the Public Key field,
   a node compatible with [RFC3972] only will extract the RSA public key
   from the Public Key field and ignore the extension fields.
   Therefore, in order to achieve backward compatibility, if a node uses
   a CGA associated with multiple public keys (through the use of the
   Public Key extension), the following procedures are in place: if one
   of the public keys is of RSA type, then that key SHOULD be placed in
   the Public Key field of the CGA Parameters data structure, while the
   other key(s) SHOULD be placed in the Extension field(s).








































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4.  Security Consideration

   The document specifies a CGA extension field format.  No additional
   vulnerabilities appear besides those described in section 7 of
   [RFC3972]

   However, it should be noted that the resulting security level of a
   multiple-key CGA, that this document made possible to use, is only
   that of the weakest key.  Therefore, as the document [RFC3972] state,
   when RSA is used, the RSA key length SHOULD be at least 384 bits.  In
   this document, we state that every key in use SHOULD have a security
   level matching or exceeding that of a 384-bit RSA key.

   Whenever protocols negotiate signature algorithms, downgrade attacks
   are considered.  This document only provides the ability for CGA
   options to carry multiple public keys; negotiations of signature
   algorithms or public keys are out of the scope of this document.


































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5.  IANA Considerations

   This document defines one new CGA Extension Type [RFC4581] option,
   which must be assigned by IANA:

      Name: Public Key Extension Type;

      Value: TBA.

      Description: see Section 2.









































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6.  References

6.1.  Normative References

   [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.

   [RFC3972]  Aura, T., "Cryptographically Generated Addresses (CGA)",
              RFC 3972, March 2005.

   [RFC3971]  Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure
              Neighbor Discovery (SEND)", RFC 3971, March 2005.

   [RFC4982]  Bagnulo, M. and J. Arkko, "Support for Multiple Hash
              Algorithms in Cryptographically Generated Addresses
              (CGAs)", RFC 4982, July 2007.

   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              September 2007.

6.2.  Informative References

   [RFC4581]  Bagnulo, M. and J. Arkko, "Cryptographically Generated
              Addresses (CGA) Extension Field Format", RFC 4581,
              October 2006.

   [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.

   [RFC4866]  Arkko, J., Vogt, C., and W. Haddad, "Enhanced Route
              Optimization for Mobile IPv6", RFC 4866, May 2007.

   [RFC5480]  Turner, S., Brown, D., Yiu, K., Housley, R., and T. Polk,
              "Elliptic Curve Cryptography Subject Public Key
              Information", RFC 5480, March 2009.

   [ITU.X690.2002]
              International Telecommunication Union, "Information
              Technology - ASN.1 encoding rules: Specification of Basic
              Encoding Rules (BER), Canonical Encoding Rules (CER) and
              Distinguished Encoding Rules (DER)", ITU-T
              Recommandation X.690, July 2002.




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   [cheneau-send-sig-agility]
              Cheneau, T., Laurent-Maknavicius, M., Shen, S., and M.
              Vanderveen, "Signature Algorithm Agility in the Secure
              Neighbor Discovery (SEND) Protocol",
              draft-cheneau-send-sig-agility-01 (work in progress),
              June 2009.













































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Authors' Addresses

   Tony Cheneau
   Institut TELECOM, TELECOM SudParis, CNRS SAMOVAR UMR 5157
   9 rue Charles Fourier
   Evry  91011
   France

   Email: tony.cheneau@it-sudparis.eu


   Maryline Laurent-Maknavicius
   Institut TELECOM, TELECOM SudParis, CNRS SAMOVAR UMR 5157
   9 rue Charles Fourier
   Evry  91011
   France

   Email: maryline.maknavicius@it-sudparis.eu


   Sean Shen
   Huawei

   Email: sshen@huawei.com


   Michaela Vanderveen
   Qualcomm

   Email: mvandervn@gmail.com





















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