RSA/SHA-1 SIGs and RSA KEYs in the Domain Name System (DNS)
RFC 3110

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• 03

Network Working Group                                    D. Eastlake 3rd
Request for Comments: 3110                                      Motorola
Obsoletes: 2537                                                 May 2001
Category: Standards Track

      RSA/SHA-1 SIGs and RSA 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 (2001).  All Rights Reserved.

Abstract

   This document describes how to produce RSA/SHA1 SIG resource records
   (RRs) in Section 3 and, so as to completely replace RFC 2537,
   describes how to produce RSA KEY RRs in Section 2.

   Since the adoption of a Proposed Standard for RSA signatures in the
   DNS (Domain Name Space), advances in hashing have been made.  A new
   DNS signature algorithm is defined to make these advances available
   in SIG RRs.  The use of the previously specified weaker mechanism is
   deprecated.  The algorithm number of the RSA KEY RR is changed to
   correspond to this new SIG algorithm.  No other changes are made to
   DNS security.

Acknowledgements

   Material and comments from the following have been incorporated and
   are gratefully acknowledged:

      Olafur Gudmundsson

      The IESG

      Charlie Kaufman

      Steve Wang

D. Eastlake 3rd             Standards Track                     [Page 1]
RFC 3110              RSA SIGs and KEYs in the DNS              May 2001

Table of Contents

   1. Introduction................................................... 2
   2. RSA Public KEY Resource Records................................ 3
   3. RSA/SHA1 SIG Resource Records.................................. 3
   4. Performance Considerations..................................... 4
   5. IANA Considerations............................................ 5
   6. Security Considerations........................................ 5
   References........................................................ 5
   Author's Address.................................................. 6
   Full Copyright Statement.......................................... 7

1. Introduction

   The Domain Name System (DNS) is the global hierarchical replicated
   distributed database system for Internet addressing, mail proxy, and
   other information [RFC1034, 1035, etc.].  The DNS has been extended
   to include digital signatures and cryptographic keys as described in
   [RFC2535].  Thus the DNS can now be secured and used for secure key
   distribution.

   Familiarity with the RSA and SHA-1 algorithms is assumed [Schneier,
   FIP180] in this document.

   RFC 2537 described how to store RSA keys and RSA/MD5 based signatures
   in the DNS.  However, since the adoption of RFC 2537, continued
   cryptographic research has revealed hints of weakness in the MD5
   [RFC1321] algorithm used in RFC 2537.  The SHA1 Secure Hash Algorithm
   [FIP180], which produces a larger hash, has been developed.  By now
   there has been sufficient experience with SHA1 that it is generally
   acknowledged to be stronger than MD5.  While this stronger hash is
   probably not needed today in most secure DNS zones, critical zones
   such a root, most top level domains, and some second and third level
   domains, are sufficiently valuable targets that it would be negligent
   not to provide what are generally agreed to be stronger mechanisms.
   Furthermore, future advances in cryptanalysis and/or computer speeds
   may require a stronger hash everywhere.  In addition, the additional
   computation required by SHA1 above that required by MD5 is
   insignificant compared with the computational effort required by the
   RSA modular exponentiation.

   This document describes how to produce RSA/SHA1 SIG RRs in Section 3
   and, so as to completely replace RFC 2537, describes how to produce
   RSA KEY RRs in Section 2.

   Implementation of the RSA algorithm in DNS with SHA1 is MANDATORY for
   DNSSEC.  The generation of RSA/MD5 SIG RRs as described in RFC 2537
   is NOT RECOMMENDED.

D. Eastlake 3rd             Standards Track                     [Page 2]
RFC 3110              RSA SIGs and KEYs in the DNS              May 2001

   The key words "MUST", "REQUIRED", "SHOULD", "RECOMMENDED", "NOT
   RECOMMENDED", and "MAY" in this document are to be interpreted as
   described in RFC 2119.

2. RSA Public KEY Resource Records

   RSA public keys are stored in the DNS as KEY RRs using algorithm
   number 5 [RFC2535].  The structure of the algorithm specific portion
   of the RDATA part of such RRs is as shown below.

         Field             Size
         -----             ----
         exponent length   1 or 3 octets (see text)