DSA KEYs and SIGs in the Domain Name System (DNS)
RFC 2536

Document Type RFC - Proposed Standard (March 1999; No errata)
Updated by RFC 6944
Last updated 2013-03-02
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IESG IESG state RFC 2536 (Proposed Standard)
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Network Working Group                                        D. EastLake
Request for Comments: 2536                                           IBM
Category: Standards Track                                     March 1999

           DSA KEYs and SIGs 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 US Government Digital Signature
   Algorithm keys and signatures in the Domain Name System is described
   which utilizes DNS KEY and SIG resource records.

Table of Contents

   Abstract...................................................1
   1. Introduction............................................1
   2. DSA KEY Resource Records................................2
   3. DSA SIG Resource Records................................3
   4. Performance Considerations..............................3
   5. Security Considerations.................................4
   6. IANA Considerations.....................................4
   References.................................................5
   Author's Address...........................................5
   Full Copyright Statement...................................6

1. Introduction

   The Domain Name System (DNS) is the global hierarchical replicated
   distributed database system for Internet addressing, mail proxy, and
   other information. The DNS has been extended to include digital
   signatures and cryptographic keys as described in [RFC 2535].  Thus
   the DNS can now be secured and can be used for secure key
   distribution.

Eastlake                    Standards Track                     [Page 1]
RFC 2536                     DSA in the DNS                   March 1999

   This document describes how to store US Government Digital Signature
   Algorithm (DSA) keys and signatures in the DNS.  Familiarity with the
   US Digital Signature Algorithm is assumed [Schneier].  Implementation
   of DSA is mandatory for DNS security.

2. DSA KEY Resource Records

   DSA public keys are stored in the DNS as KEY RRs using algorithm
   number 3 [RFC 2535].  The structure of the algorithm specific portion
   of the RDATA part of this RR is as shown below.  These fields, from Q
   through Y are the "public key" part of the DSA 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.

           Field     Size
           -----     ----
            T         1  octet
            Q        20  octets
            P        64 + T*8  octets
            G        64 + T*8  octets
            Y        64 + T*8  octets

   As described in [FIPS 186] and [Schneier]: T is a key size parameter
   chosen such that 0 <= T <= 8.  (The meaning for algorithm 3 if the T
   octet is greater than 8 is reserved and the remainder of the RDATA
   portion may have a different format in that case.)  Q is a prime
   number selected at key generation time such that 2**159 < Q < 2**160
   so Q is always 20 octets long and, as with all other fields, is
   stored in "big-endian" network order.  P, G, and Y are calculated as
   directed by the FIPS 186 key generation algorithm [Schneier].  P is
   in the range 2**(511+64T) < P < 2**(512+64T) and so is 64 + 8*T
   octets long.  G and Y are quantities modulus P and so can be up to
   the same length as P and are allocated fixed size fields with the
   same number of octets as P.

   During the key generation process, a random number X must be
   generated such that 1 <= X <= Q-1.  X is the private key and is used
   in the final step of public key generation where Y is computed as

             Y = G**X mod P

Eastlake                    Standards Track                     [Page 2]
RFC 2536                     DSA in the DNS                   March 1999

3. DSA SIG Resource Records

   The signature portion of the SIG RR RDATA area, when using the US
   Digital Signature Algorithm, is shown below with fields in the order
   they occur.  See [RFC 2535] for fields in the SIG RR RDATA which
   precede the signature itself.

           Field     Size
           -----     ----
            T         1 octet
            R        20 octets
            S        20 octets
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