
INTERNET-DRAFT                     Diffie-Hellman Information in the DNS
OBSOLETES: RFC 2539                               Donald E. Eastlake 3rd
                                                   Motorola Laboratories
Expires: September 2006                                       March 2006




        Storage of Diffie-Hellman Keying Information in the DNS
        ------- -- -------------- ------ ----------- -- --- ---
               <draft-ietf-dnsext-rfc2539bis-dhk-07.txt>



Status of This Document

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Abstract

   The standard method for encoding Diffie-Hellman keys in the Domain
   Name System is specified.









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Acknowledgements

   Part of the format for Diffie-Hellman keys and the description
   thereof was taken from a work in progress by Ashar Aziz, Tom Markson,
   and Hemma Prafullchandra.  In addition, the following persons
   provided useful comments that were incorporated into the predecessor
   of this document: Ran Atkinson, Thomas Narten.



Table of Contents

          Status of This Document....................................1
      Abstract...................................................1

      Acknowledgements...........................................2
      Table of Contents..........................................2

      1. Introduction............................................3
      1.1 About This Document....................................3
      1.2 About Diffie-Hellman...................................3
      2. Encoding Diffie-Hellman Keying Information..............4
      3. Performance Considerations..............................5
      4. IANA Considerations.....................................5
      5. Security Considerations.................................5
      Copyright, Disclaimer, and Additional IPR Provisions.......5

      Normative References.......................................7
      Informative Refences.......................................7

      Author's Address...........................................8
      Expiration and File Name...................................8

      Appendix A: Well known prime/generator pairs...............9
      A.1. Well-Known Group 1:  A 768 bit prime..................9
      A.2. Well-Known Group 2:  A 1024 bit prime.................9
      A.3. Well-Known Group 3:  A 1536 bit prime................10















D. Eastlake 3rd                                                 [Page 2]


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1. Introduction

   The Domain Name System (DNS) is the global hierarchical replicated
   distributed database system for Internet addressing, mail proxy, and
   similar information [RFC 1034, 1035]. The DNS has been extended to
   include digital signatures and cryptographic keys as described in
   [RFC 4033, 4034, 4035] and additonal work is underway which would use
   the storage of keying information in the DNS.



1.1 About This Document

   This document describes how to store Diffie-Hellman keys in the DNS.
   Familiarity with the Diffie-Hellman key exchange algorithm is assumed
   [Schneier, RFC 2631].

   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 RFC 2119.



1.2 About Diffie-Hellman

   Diffie-Hellman requires two parties to interact to derive keying
   information which can then be used for authentication.  Thus Diffie-
   Hellman is inherently a key agreement algorithm. As a result, no
   format is defined for Diffie-Hellman "signature information".  For
   example, assume that two parties have local secrets "i" and "j".
   Assume they each respectively calculate X and Y as follows:

        X = g**i ( mod p )

        Y = g**j ( mod p )

   They exchange these quantities and then each calculates a Z as
   follows:

        Zi = Y**i ( mod p )

        Zj = X**j ( mod p )

   Zi and Zj will both be equal to g**(i*j)(mod p) and will be a shared
   secret between the two parties that an adversary who does not know i
   or j will not be able to learn from the exchanged messages (unless
   the adversary can derive i or j by performing a discrete logarithm
   mod p which is hard for strong p and g).

   The private key for each party is their secret i (or j).  The public


D. Eastlake 3rd                                                 [Page 3]


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   key is the pair p and g, which is the same for both parties, and
   their individual X (or Y).

   For further information about Diffie-Hellman and precautions to take
   in deciding on a p and g, see [RFC 2631].



2. Encoding Diffie-Hellman Keying Information

   When Diffie-Hellman keys appear within the RDATA portion of a RR,
   they are encoded as shown below.

   The period of key validity is not included in this data but is
   indicated separately, for example by an RR such as RRSIG which signs
   and authenticates the RR containing the keying information.

                            1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |           KEY flags           |    protocol   |  algorithm=2  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |     prime length (or flag)    |  prime (p) (or special)       /
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       /  prime (p)  (variable length) |       generator length        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | generator (g) (variable length)                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |     public value length       | public value (variable length)/
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       /  public value (g^i mod p)    (variable length)                |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Prime length is the length of the Diffie-Hellman prime (p) in bytes
   if it is 16 or greater.  Prime contains the binary representation of
   the Diffie-Hellman prime with most significant byte first (i.e., in
   network order). If "prime length" field is 1 or 2, then the "prime"
   field is actually an unsigned index into a table of 65,536
   prime/generator pairs and the generator length SHOULD be zero.  See
   Appedix A for defined table entries and Section 4 for information on
   allocating additional table entries.  The meaning of a zero or 3
   through 15 value for "prime length" is reserved.

   Generator length is the length of the generator (g) in bytes.
   Generator is the binary representation of generator with most
   significant byte first.  PublicValueLen is the Length of the Public
   Value (g**i (mod p)) in bytes.  PublicValue is the binary
   representation of the DH public value with most significant byte
   first.



D. Eastlake 3rd                                                 [Page 4]


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3. Performance Considerations

   Current DNS implementations are optimized for small transfers,
   typically less than 512 bytes including DNS overhead.  Larger
   transfers will perform correctly and extensions have been
   standardized [RFC 2671] to make larger transfers more efficient. But
   it is still advisable at this time to make reasonable efforts to
   minimize the size of RR sets containing keying information consistent
   with adequate security.



4. IANA Considerations

   Assignment of meaning to Prime Lengths of 0 and 3 through 15 requires
   an IETF consensus as defined in [RFC 2434].

   Well known prime/generator pairs number 0x0000 through 0x07FF can
   only be assigned by an IETF standards action. [RFC 2539], the
   Proposed Standard predecessor of this document, assigned 0x0001
   through 0x0002. This document additionally assigns 0x0003.  Pairs
   number 0s0800 through 0xBFFF can be assigned based on RFC
   documentation. Pairs number 0xC000 through 0xFFFF are available for
   private use and are not centrally coordinated. Use of such private
   pairs outside of a closed environment may result in conflicts and/or
   security failures.



5. Security Considerations

   Keying information retrieved from the DNS should not be trusted
   unless (1) it has been securely obtained from a secure resolver or
   independently verified by the user and (2) this secure resolver and
   secure obtainment or independent verification conform to security
   policies acceptable to the user.  As with all cryptographic
   algorithms, evaluating the necessary strength of the key is important
   and dependent on security policy.

   In addition, the usual Diffie-Hellman key strength considerations
   apply. (p-1)/2 SHOULD also be prime, g SHOULD be primitive mod p, p
   SHOULD be "large", etc. See [RFC 2631, Schneier].



Copyright, Disclaimer, and Additional IPR Provisions

   Copyright (C) The Internet Society (2006).  This document is subject to
   the rights, licenses and restrictions contained in BCP 78, and except
   as set forth therein, the authors retain all their rights.


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   This document and the information contained herein are provided on an
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   Copies of IPR disclosures made to the IETF Secretariat and any
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   The IETF invites any interested party to bring to its attention any
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   this standard.  Please address the information to the IETF at ietf-
   ipr@ietf.org.























D. Eastlake 3rd                                                 [Page 6]


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Normative References

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

   [RFC 2434] - "Guidelines for Writing an IANA Considerations Section
   in RFCs", T.  Narten, H. Alvestrand, October 1998.

   [RFC 2631] - "Diffie-Hellman Key Agreement Method", E. Rescorla, June
   1999.

   [RFC 4034] - Arends, R., Austein, R., Larson, M., Massey, D., and S.
   Rose, "Resource Records for the DNS Security Extensions", RFC 4034,
   March 2005.



Informative Refences

   [RFC 1034] - "Domain names - concepts and facilities", P.
   Mockapetris, November 1987.

   [RFC 1035] - "Domain names - implementation and specification", P.
   Mockapetris, November 1987.

   [RFC 2539] - "Storage of Diffie-Hellman Keys in the Domain Name
   System (DNS)", D. Eastlake, March 1999, obsoleted by this RFC.

   [RFC 2671] - "Extension Mechanisms for DNS (EDNS0)", P. Vixie, August
   1999.

   [RFC 4033] - Arends, R., Austein, R., Larson, M., Massey, D., and S.
   Rose, "DNS Security Introduction and Requirements", RFC 4033, March
   2005.

   [RFC 4035] - Arends, R., Austein, R., Larson, M., Massey, D., and S.
   Rose, "Protocol Modifications for the DNS Security Extensions", RFC
   4035, March 2005.

   [Schneier] - Bruce Schneier, "Applied Cryptography: Protocols,
   Algorithms, and Source Code in C" (Second Edition), 1996, John Wiley
   and Sons.










D. Eastlake 3rd                                                 [Page 7]


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Author's Address

   Donald E. Eastlake 3rd
   Motorola Laboratories
   155 Beaver Street
   Milford, MA 01757 USA

   Telephone:   +1-508-786-7554
   EMail:       Donald.Eastlake@motorola.com



Expiration and File Name

   This draft expires in September 2006.

   Its file name is draft-ietf-dnsext-rfc2539bis-dhk-07.txt.



































D. Eastlake 3rd                                                 [Page 8]


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Appendix A: Well known prime/generator pairs

   These numbers are copied from the IPSEC effort where the derivation
   of these values is more fully explained and additional information is
   available.  Richard Schroeppel performed all the mathematical and
   computational work for this appendix.



A.1. Well-Known Group 1:  A 768 bit prime

   The prime is 2^768 - 2^704 - 1 + 2^64 * { [2^638 pi] + 149686 }.  Its
   decimal value is
          155251809230070893513091813125848175563133404943451431320235
          119490296623994910210725866945387659164244291000768028886422
          915080371891804634263272761303128298374438082089019628850917
          0691316593175367469551763119843371637221007210577919

   Prime modulus: Length (32 bit words): 24, Data (hex):
            FFFFFFFF FFFFFFFF C90FDAA2 2168C234 C4C6628B 80DC1CD1
            29024E08 8A67CC74 020BBEA6 3B139B22 514A0879 8E3404DD
            EF9519B3 CD3A431B 302B0A6D F25F1437 4FE1356D 6D51C245
            E485B576 625E7EC6 F44C42E9 A63A3620 FFFFFFFF FFFFFFFF

   Generator: Length (32 bit words): 1, Data (hex): 2



A.2. Well-Known Group 2:  A 1024 bit prime

   The prime is 2^1024 - 2^960 - 1 + 2^64 * { [2^894 pi] + 129093 }.
   Its decimal value is
         179769313486231590770839156793787453197860296048756011706444
         423684197180216158519368947833795864925541502180565485980503
         646440548199239100050792877003355816639229553136239076508735
         759914822574862575007425302077447712589550957937778424442426
         617334727629299387668709205606050270810842907692932019128194
         467627007

   Prime modulus:  Length (32 bit words): 32, Data (hex):
            FFFFFFFF FFFFFFFF C90FDAA2 2168C234 C4C6628B 80DC1CD1
            29024E08 8A67CC74 020BBEA6 3B139B22 514A0879 8E3404DD
            EF9519B3 CD3A431B 302B0A6D F25F1437 4FE1356D 6D51C245
            E485B576 625E7EC6 F44C42E9 A637ED6B 0BFF5CB6 F406B7ED
            EE386BFB 5A899FA5 AE9F2411 7C4B1FE6 49286651 ECE65381
            FFFFFFFF FFFFFFFF

   Generator: Length (32 bit words): 1, Data (hex): 2




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A.3. Well-Known Group 3:  A 1536 bit prime

   The prime is 2^1536 - 2^1472 - 1 + 2^64 * { [2^1406 pi] +  741804 }.
   Its decimal value is
            241031242692103258855207602219756607485695054850245994265411
            694195810883168261222889009385826134161467322714147790401219
            650364895705058263194273070680500922306273474534107340669624
            601458936165977404102716924945320037872943417032584377865919
            814376319377685986952408894019557734611984354530154704374720
            774996976375008430892633929555996888245787241299381012913029
            459299994792636526405928464720973038494721168143446471443848
            8520940127459844288859336526896320919633919

   Prime modulus Length (32 bit words): 48, Data (hex):
              FFFFFFFF FFFFFFFF C90FDAA2 2168C234 C4C6628B 80DC1CD1
              29024E08 8A67CC74 020BBEA6 3B139B22 514A0879 8E3404DD
              EF9519B3 CD3A431B 302B0A6D F25F1437 4FE1356D 6D51C245
              E485B576 625E7EC6 F44C42E9 A637ED6B 0BFF5CB6 F406B7ED
              EE386BFB 5A899FA5 AE9F2411 7C4B1FE6 49286651 ECE45B3D
              C2007CB8 A163BF05 98DA4836 1C55D39A 69163FA8 FD24CF5F
              83655D23 DCA3AD96 1C62F356 208552BB 9ED52907 7096966D
              670C354E 4ABC9804 F1746C08 CA237327 FFFFFFFF FFFFFFFF

   Generator: Length (32 bit words):  1, Data (hex): 2




























D. Eastlake 3rd                                                [Page 10]

