


DNS Extensions working group                                   J. Jansen
Internet-Draft                                                NLnet Labs
Expires: July 5, 2006                                       January 2006


     Use of RSA/SHA-256 DNSKEY and RRSIG Resource Records in DNSSEC
                 draft-ietf-dnsext-dnssec-rsasha256-00

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Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   This document describes how to produce RSA/SHA-256 DNSKEY and RRSIG
   resource records for use in the Domain Name System Security
   Extensions (DNSSEC, RFC4033, RFC4034, and RFC4035).









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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  RSA/SHA-256 DNSKEY Resource Records . . . . . . . . . . . . . . 3
   3.  RSA/SHA-256 RRSIG Resource Records  . . . . . . . . . . . . . . 3
   4.  Implementation Considerations . . . . . . . . . . . . . . . . . 4
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4
   6.  Security Considerations . . . . . . . . . . . . . . . . . . . . 4
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 5
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 5
     8.1.  Normative References  . . . . . . . . . . . . . . . . . . . 5
     8.2.  Informative References  . . . . . . . . . . . . . . . . . . 5
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 6
   Intellectual Property and Copyright Statements  . . . . . . . . . . 7





































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1.  Introduction

   The Domain Name System (DNS) is the global hierarchical distributed
   database for Internet Addressing.  The DNS has been extended to use
   digital signatures and cryptographic keys for the verification of
   data.  RFC4033 [1], RFC4034 [2], and RFC4035 [3] describe these DNS
   Security Extensions.

   RFC4034 describes how to store DNSKEY and RRSIG resource records, and
   specifies a list of cryptographic algorithms to use.  This document
   extends that list with the algorithm RSA/SHA-256, and specifies how
   to store RSA/SHA-256 DNSKEY data and how to produce RSA/SHA-256 RRSIG
   resource records.

   Familiarity with the RSA [7] and SHA-256 [5] algorithms is assumed in
   this document.


2.  RSA/SHA-256 DNSKEY Resource Records

   RSA public keys for use with RSA/SHA-256 are stored in DNSKEY
   resource records (RRs) with the algorithm number [TBA].

   The format of the DNSKEY RR can be found in RFC4034 [2] and RFC3110
   [6].


3.  RSA/SHA-256 RRSIG Resource Records

   RSA/SHA-256 signatures are stored in the DNS using RRSIG resource
   records (RRs) with algorithm number [TBA].

   The value of the signature field in the RRSIG RR is calculated as
   follows.  The values for the fields that precede the signature data
   are specified in RFC4034 [2].

   hash = SHA-256(data)

   signature = ( 00 | 01 | FF* | 00 | prefix | hash ) ** e (mod n)

   Where SHA-256 is the message digest algorithm as specified in FIPS
   180 [5], | is concatenation, 00, 01, FF and 00 are fixed octets of
   corresponding hexadecimal value, "e" is the private exponent of the
   signing RSA key, and "n" is the public modulus of the signing key.
   The FF octet MUST be repeated the maximum number of times so that the
   total length of the signature equals the length of the modulus of the
   signer's public key ("n"). "data" is the data of the resource record
   set that is signed, as specified in RFC4034 [2].



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   The prefix is the ASN.1 BER SHA-256 algorithm designator prefix as
   specified in PKCS 2.1 [4]:

   hex 30 31 30 0d 06 09 60 86 48 01 65 03 04 02 01 05 00 04 20

   This prefix should make the use of standard cryptographic libraries
   easier.  These specifications are taken directly from PKCS #1 v2.1
   section 9.2 [4].


4.  Implementation Considerations

   DNSSEC aware implementations MUST be able to support RRSIG resource
   records with the RSA/SHA-256 algorithm.

   If both RSA/SHA-256 and RSA/SHA-1 RRSIG resource records are
   available for a certain rrset, with a secure path to their keys, the
   validator SHOULD ignore the SHA-1 signature.  If the RSA/SHA-256
   signature does not verify the data, and the RSA/SHA-1 does, the
   validator SHOULD mark the data with the security status from the RSA/
   SHA-256 signature.


5.  IANA Considerations

   IANA has not yet assigned an algorithm number for RSA/SHA-256.

   The algorithm list from RFC4034 Appendix A.1 [2] is extended with the
   following entry:

                                   Zone
   Value Algorithm    [Mnemonic] Signing  References   Status
   ----- ----------- ----------- -------- ----------  ---------
   [tba] RSA/SHA-256 [RSASHA256]      y        [TBA]  MANDATORY


6.  Security Considerations

   Recently, weaknesses have been discovered in the SHA-1 hashing
   algorithm.  It is therefore strongly encouraged to deploy SHA-256
   where SHA-1 is used now, as soon as the DNS software supports it.

   SHA-256 is considered sufficiently strong for the immediate future,
   but predictions about future development in cryptography and
   cryptanalysis are beyond the scope of this document.






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7.  Acknowledgments

   This document is a minor extension to RFC4034 [2].  Also, we try to
   follow the documents RFC3110 [6] and draft-ietf-dnsext-ds-sha256.txt
   [8] for consistency.  The authors of and contributors to these
   documents are gratefully acknowledged for their hard work.

   The following people provided additional feedback and text: Jaap
   Akkerhuis, Miek Gieben and Wouter Wijngaards.


8.  References

8.1.  Normative References

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

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

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

   [4]  Jonsson, J. and B. Kaliski, "Public-Key Cryptography Standards
        (PKCS) #1: RSA Cryptography Specifications Version 2.1",
        RFC 3447, February 2003.

   [5]  National Institute of Standards and Technology, "Secure Hash
        Standard", FIPS PUB 180-2, August 2002.

   [6]  Eastlake, D., "RSA/SHA-1 SIGs and RSA KEYs in the Domain Name
        System (DNS)", RFC 3110, May 2001.

8.2.  Informative References

   [7]  Schneier, B., "Applied Cryptography Second Edition: protocols,
        algorithms, and source code in C", Wiley and Sons , ISBN 0-471-
        11709-9, 1996.

   [8]  Hardaker, W., "Use of SHA-256 in DNSSEC Delegation Signer (DS)
        Resource Records (RRs)", Work in Progress Feb 2006.






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Author's Address

   Jelte Jansen
   NLnet Labs
   Kruislaan 419
   Amsterdam  1098VA
   NL

   Email: jelte@NLnetLabs.nl
   URI:   http://www.nlnetlabs.nl/









































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