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+Network Working Group                                        D. Eastlake
+Request for Comments: 2539                                           IBM
+Category: Standards Track                                     March 1999
+
+
+     Storage of Diffie-Hellman Keys in the Domain Name System (DNS)
+
+Status of this Memo
+
+   This document specifies an Internet standards track protocol for the
+   Internet community, and requests discussion and suggestions for
+   improvements.  Please refer to the current edition of the "Internet
+   Official Protocol Standards" (STD 1) for the standardization state
+   and status of this protocol.  Distribution of this memo is unlimited.
+
+Copyright Notice
+
+   Copyright (C) The Internet Society (1999).  All Rights Reserved.
+
+Abstract
+
+   A standard method for storing Diffie-Hellman keys in the Domain Name
+   System is described which utilizes DNS KEY resource records.
+
+Acknowledgements
+
+   Part of the format for Diffie-Hellman keys and the description
+   thereof was taken from a work in progress by:
+
+      Ashar Aziz <ashar.aziz@eng.sun.com>
+      Tom Markson <markson@incog.com>
+      Hemma Prafullchandra <hemma@eng.sun.com>
+
+   In addition, the following person provided useful comments that have
+   been incorporated:
+
+      Ran Atkinson <rja@inet.org>
+      Thomas Narten <narten@raleigh.ibm.com>
+
+
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+Eastlake                    Standards Track                     [Page 1]
+
+RFC 2539             Diffie-Hellman Keys in the DNS           March 1999
+
+
+Table of Contents
+
+   Abstract...................................................1
+   Acknowledgements...........................................1
+   1. Introduction............................................2
+   1.1 About This Document....................................2
+   1.2 About Diffie-Hellman...................................2
+   2. Diffie-Hellman KEY Resource Records.....................3
+   3. Performance Considerations..............................4
+   4. IANA Considerations.....................................4
+   5. Security Considerations.................................4
+   References.................................................5
+   Author's Address...........................................5
+   Appendix A: Well known prime/generator pairs...............6
+   A.1. Well-Known Group 1:  A 768 bit prime..................6
+   A.2. Well-Known Group 2:  A 1024 bit prime.................6
+   Full Copyright Notice......................................7
+
+1. Introduction
+
+   The Domain Name System (DNS) is the current global hierarchical
+   replicated distributed database system for Internet addressing, mail
+   proxy, and similar information. The DNS has been extended to include
+   digital signatures and cryptographic keys as described in [RFC 2535].
+   Thus the DNS can now be used for secure key distribution.
+
+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].
+
+1.2 About Diffie-Hellman
+
+   Diffie-Hellman requires two parties to interact to derive keying
+   information which can then be used for authentication.  Since DNS SIG
+   RRs are primarily used as stored authenticators of zone information
+   for many different resolvers, no Diffie-Hellman algorithm SIG RR is
+   defined. 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 )
+
+
+
+
+Eastlake                    Standards Track                     [Page 2]
+
+RFC 2539             Diffie-Hellman Keys in the DNS           March 1999
+
+
+   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
+   key is the pair p and g, which must be the same for the parties, and
+   their individual X (or Y).
+
+2. Diffie-Hellman KEY Resource Records
+
+   Diffie-Hellman keys are stored in the DNS as KEY RRs using algorithm
+   number 2.  The structure of the RDATA portion of this RR is as shown
+   below.  The first 4 octets, including the flags, protocol, and
+   algorithm fields are common to all KEY RRs as described in [RFC
+   2535].  The remainder, from prime length through public value is the
+   "public key" part of the KEY RR. The period of key validity is not in
+   the KEY RR but is indicated by the SIG RR(s) which signs and
+   authenticates the KEY RR(s) at that domain name.
+
+                         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 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.
+
+
+
+
+
+
+Eastlake                    Standards Track                     [Page 3]
+
+RFC 2539             Diffie-Hellman Keys in the DNS           March 1999
+
+
+   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.
+
+   The corresponding algorithm=2 SIG resource record is not used so no
+   format for it is defined.
+
+3. Performance Considerations
+
+   Current DNS implementations are optimized for small transfers,
+   typically less than 512 bytes including overhead.  While larger
+   transfers will perform correctly and work is underway to make larger
+   transfers more efficient, it is still advisable to make reasonable
+   efforts to minimize the size of KEY RR sets stored within the DNS
+   consistent with adequate security.  Keep in mind that in a secure
+   zone, an authenticating SIG RR will also be returned.
+
+4. IANA Considerations
+
+   Assignment of meaning to Prime Lengths of 0 and 3 through 15 requires
+   an IETF consensus.
+
+   Well known prime/generator pairs number 0x0000 through 0x07FF can
+   only be assigned by an IETF standards action and this Proposed
+   Standard assigns 0x0001 through 0x0002. 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.
+
+5. Security Considerations
+
+   Many of the general security consideration in [RFC 2535] apply.  Keys
+   retrieved from the DNS should not be trusted unless (1) they have
+   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 local 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.  [Schneier]
+
+
+
+
+Eastlake                    Standards Track                     [Page 4]
+
+RFC 2539             Diffie-Hellman Keys in the DNS           March 1999
+
+
+References
+
+   [RFC 1034]   Mockapetris, P., "Domain Names - Concepts and
+                Facilities", STD 13, RFC 1034, November 1987.
+
+   [RFC 1035]   Mockapetris, P., "Domain Names - Implementation and
+                Specification", STD 13, RFC 1035, November 1987.
+
+   [RFC 2535]   Eastlake, D., "Domain Name System Security Extensions",
+                RFC 2535, March 1999.
+
+   [Schneier]   Bruce Schneier, "Applied Cryptography: Protocols,
+                Algorithms, and Source Code in C", 1996, John Wiley and
+                Sons
+
+Author's Address
+
+   Donald E. Eastlake 3rd
+   IBM
+   65 Shindegan Hill Road, RR #1
+   Carmel, NY 10512
+
+   Phone:   +1-914-276-2668(h)
+            +1-914-784-7913(w)
+   Fax:     +1-914-784-3833(w)
+   EMail:   dee3@us.ibm.com
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+Eastlake                    Standards Track                     [Page 5]
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+RFC 2539             Diffie-Hellman Keys in the DNS           March 1999
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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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+
+
+Eastlake                    Standards Track                     [Page 6]
+
+RFC 2539             Diffie-Hellman Keys in the DNS           March 1999
+
+
+Full Copyright Statement
+
+   Copyright (C) The Internet Society (1999).  All Rights Reserved.
+
+   This document and translations of it may be copied and furnished to
+   others, and derivative works that comment on or otherwise explain it
+   or assist in its implementation may be prepared, copied, published
+   and distributed, in whole or in part, without restriction of any
+   kind, provided that the above copyright notice and this paragraph are
+   included on all such copies and derivative works.  However, this
+   document itself may not be modified in any way, such as by removing
+   the copyright notice or references to the Internet Society or other
+   Internet organizations, except as needed for the purpose of
+   developing Internet standards in which case the procedures for
+   copyrights defined in the Internet Standards process must be
+   followed, or as required to translate it into languages other than
+   English.
+
+   The limited permissions granted above are perpetual and will not be
+   revoked by the Internet Society or its successors or assigns.
+
+   This document and the information contained herein is provided on an
+   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
+   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
+   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
+   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
+   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
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+Eastlake                    Standards Track                     [Page 7]
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