Storage of Diffie-Hellman Keys in the Domain Name System (DNS)
RFC 2539

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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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 )

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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