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INTERNET-DRAFT                                DSA Information in the DNS
OBSOLETES: RFC 2536                               Donald E. Eastlake 3rd
                                                   Motorola Laboratories
Expires: April 2007                                         October 2006


            DSA Keying and Signature Information in the DNS
            --- ------ --- --------- ----------- -- --- ---
               <draft-ietf-dnsext-rfc2536bis-dsa-08.txt>
                         Donald E. Eastlake 3rd


Status of This Document

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
   aware will be disclosed, in accordance with Section 6 of BCP 79.

   Distribution of this document is unlimited. Comments should be sent
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   <namedroppers@ops.ietf.org>.

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Abstract

   The standard method of encoding US Government Digital Signature
   Algorithm keying and signature information for use in the Domain Name
   System is specified.









D. Eastlake 3rd                                                 [Page 1]


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Table of Contents

      Status of This Document....................................1
      Abstract...................................................1

      Table of Contents..........................................2

      1. Introduction............................................3
      2. DSA Keying Information..................................3
      3. DSA Signature Information...............................4
      4. Performance Considerations..............................4
      5. Security Considerations.................................5
      6. IANA Considerations.....................................5
      Appendix A: Example RRs....................................5
      Appendix B: Changes from RFC 2536..........................7
      Copyright, Disclaimer, and Additional IPR Provisions.......7

      Normative References.......................................9
      Informative References.....................................9

      Author's Address..........................................11
      Expiration and File Name..................................11






























D. Eastlake 3rd                                                 [Page 2]


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1. Introduction

   The Domain Name System (DNS) is the global hierarchical replicated
   distributed database system for Internet addressing, mail proxy, and
   other information [RFC1034], [RFC1035]. The DNS has been extended to
   include digital signatures and cryptographic keys as described in
   [RFC4033], [RFC4034], [RFC4035] and there is additional work which
   would use the storage of keying information in the DNS such as
   IPSECKEY [RFC4025]. This document does not change the wire format of
   KEY RR's but extends the use of DSA DNS keys to cover the DNSKEY RR.

   This document describes how to encode US Government Digital Signature
   Algorithm (DSA) keys and signatures in the DNS.  Familiarity with the
   US Digital Signature Algorithm is assumed [FIPS186-2], [Schneier].



2. DSA Keying Information

   When DSA public keys are stored in the DNS, the structure of the
   relevant part of the RDATA part of the RR (currently KEY and DNSKEY)
   being used is the fields listed below in the order given.

   The period of key validity is not included in this data but is
   indicated separately, for example by an RR such as RRSIG which signs
   and authenticates the RR containing the keying information.

        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 [FIPS186-2] and [Schneier], T is a key size parameter
   chosen such that 0 <= T <= 8.  (The meaning if the T octet is greater
   than 8 is reserved and the remainder of the data 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. Thus 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 [FIPS186-2] key
   generation algorithm [Schneier]. P is in the range 2**(511+64*T) < P
   < 2**(512+64*T) and thus is 64 + 8*T octets long.  G and Y are
   quantities modulo 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


D. Eastlake 3rd                                                 [Page 3]


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        Y = G**X mod P



3. DSA Signature Information

   The portion of the RDATA area used for US Digital Signature Algorithm
   signature information is shown below with fields in the order they
   are listed and the contents of each multi-octet field in "big-endian"
   network order.

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

   First, the data signed must be determined.  Then the following steps
   are taken, as specified in [FIPS186-2], where Q, P, G, and Y are as
   specified in the public key [Schneier]:

        hash = SHA-1 ( data )

        Generate a random K such that 0 < K < Q.

        R = ( G**K mod P ) mod Q

        S = ( K**(-1) * (hash + X*R) ) mod Q

   For information on the SHA-1 hash function see [FIPS180-2] and
   [RFC3174].

   Since Q is 160 bits long, R and S can not be larger than 20 octets,
   which is the space allocated.

   T is copied from the public key. It is not logically necessary in an
   RRSIG but is present so that values of T > 8 can more conveniently be
   used as an escape for extended versions of DSA or other algorithms as
   later standardized.



4. Performance Considerations

   General signature generation speeds are roughly the same for RSA
   [RFC3110] and DSA.  With sufficient pre-computation, signature
   generation with DSA is faster than RSA.  Key generation is also
   faster for DSA.  However, DSA signature verification is an order of
   magnitude slower than RSA when the RSA public exponent is chosen to
   be small, as is recommended for some applications.


D. Eastlake 3rd                                                 [Page 4]


INTERNET-DRAFT                                DSA Information in the DNS


   Current DNS implementations are optimized for small transfers,
   typically less than 512 bytes including DNS overhead.  Larger
   transfers will perform correctly and extensions have been
   standardized [RFC2671] to make larger transfers more efficient, it is
   still advisable at this time to make reasonable efforts to minimize
   the size of RR sets containing keying and/or signature information
   consistent with adequate security.



5. Security Considerations

   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 essential and
   dependent on local security policy.

   The key size limitation of a maximum of 1024 bits ( T = 8 ) in the
   referenced DSA standard [FIPS186-2] may limit the security of DSA.
   For particular applications, implementers are encouraged to consider
   the range of available algorithms and key sizes.

   DSA assumes the ability to frequently generate high quality random
   numbers. See [RFC4086] for guidance.  DSA is designed so that if
   biased rather than random numbers are used, high bandwidth covert
   channels are possible.  See [Schneier] and more recent research.  The
   leakage of an entire DSA private key in only two DSA signatures has
   been demonstrated. DSA provides security only if trusted
   implementations, including trusted random number generation, are
   used.



6. IANA Considerations

   Allocation of meaning to values of the T parameter that are not
   defined herein (i.e., > 8 ) requires an IETF standards actions.  It
   is intended that values unallocated herein be used to cover future
   extensions of the DSS standard.



Appendix A: Example RRs

   This section provides an example DNSKEY and corresponding RRSIG RR.
   All numbers below in this Appendix are in hexadecimal.



D. Eastlake 3rd                                                 [Page 5]


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   The elements of the DSA key are as follows:
      T = 00
      Q = c773218c 737ec8ee 993b4f2d ed30f48e dace915f
      P = 8df2a494 492276aa 3d25759b b06869cb eac0d83a fb8d0cf7
          cbb8324f 0d7882e5 d0762fc5 b7210eaf c2e9adac 32ab7aac
          49693dfb f83724c2 ec0736ee 31c80291
      G = 626d0278 39ea0a13 413163a5 5b4cb500 299d5522 956cefcb
          3bff10f3 99ce2c2e 71cb9de5 fa24babf 58e5b795 21925c9c
          c42e9f6f 464b088c c572af53 e6d78802
      Y = 19131871 d75b1612 a819f29d 78d1b0d7 346f7aa7 7bb62a85
          9bfd6c56 75da9d21 2d3a36ef 1672ef66 0b8c7c25 5cc0ec74
          858fba33 f44c0669 9630a76b 030ee333

   Based on this, the RDATA portion of a zone signing DSNKEY RR would be
   as show below where "F" is the flags field, "p" is the "protocol"
   field, and "a" is the algorithm field.
             01 00030300 c773218c 737ec8ee 993b4f2d ed30f48e
             F>   p>a>T> Q>
       dace915f 8df2a494 492276aa 3d25759b b06869cb eac0d83a
                P>
       fb8d0cf7 cbb8324f 0d7882e5 d0762fc5 b7210eaf c2e9adac
       32ab7aac 49693dfb f83724c2 ec0736ee 31c80291 626d0278
                                                    G>
       39ea0a13 413163a5 5b4cb500 299d5522 956cefcb 3bff10f3
       99ce2c2e 71cb9de5 fa24babf 58e5b795 21925c9c c42e9f6f
       464b088c c572af53 e6d78802 19131871 d75b1612 a819f29d
                                  Y>
       78d1b0d7 346f7aa7 7bb62a85 9bfd6c56 75da9d21 2d3a36ef
       1672ef66 0b8c7c25 5cc0ec74 858fba33 f44c0669 9630a76b
       030ee333

   The Key Tag for the above DNSKEY RDATA, whose RDLENGTH is 00d9, is
   19a3.

   Assume that the hash of the DNS data being signed is
         a9993e36 4706816a ba3e2571 7850c26c 9cd0d89d
   the resulting signature value would be
      T = 00
      R = 8bac1ab6 6410435c b7181f95 b16ab97c 92b341c0
      S = 41e2345f 1f56df24 58f426d1 55b4ba2d b6dcd8c8

   Based on this, the RDATA portion of an RRSIG with this hash is shown
   below assuming the following other parameters: the RRSIG signs "A"
   records; its validity time is from 00112233 seconds after the 1
   January 1970 00:00:00 UTC through 00123456 seconds after that time;
   the signer name of "xx."; the original TTL was one hour or 0e10
   seconds; and the number of labels in the original owner name was 05.
   "a" is the algorithm number for DSA and "l" is the "Labels" field.

       0001 03 05 00000e10 00123456 00112233 19a3 02787800


D. Eastlake 3rd                                                 [Page 6]


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       Type a> l> OrigTTL  expire   incept   ktag signer
       00 8bac1ab6 6410435c b7181f95 b16ab97c 92b341c0
       T> R>
          41e2345f 1f56df24 58f426d1 55b4ba2d b6dcd8c8
          S>

   All numbers above in this Appendix are in hexadecimal.



Appendix B: Changes from RFC 2536

   When [RFC2536] was published, keys and signatures in the DNS appeared
   only in KEY and SIG resource records. As described in [RFC3755], due
   to a revision in DNS data origin authentication security, the
   recommended RRs were changed to DNSKEY and RRSIG which are described
   in [RFC4034]; however, SIG continues to be used in transaction
   authentication, SIG(0) [RFC2931], and KEY continue to be used in
   connection with TKEY [RFC2930].

   Thus the primary change from RFC 2536 in this document is to
   eliminate the tie to the KEY and SIG RRs. In addition, many
   references have been updated and example DNSKEY and RRSIG RRs using
   the DSA algorithm have been included.



Copyright, Disclaimer, and Additional IPR Provisions

   Copyright (C) The Internet Society 2006.  This document is subject to
   the rights, licenses and restrictions contained in BCP 78, and except
   as set forth therein, the authors retain all their rights.


   This document and the information contained herein are provided on an
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
   ENGINEERING TASK FORCE DISCLAIM 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.

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; nor does it represent that it has
   made any independent effort to identify any such rights.  Information
   on the procedures with respect to rights in RFC documents can be
   found in BCP 78 and BCP 79.


D. Eastlake 3rd                                                 [Page 7]


INTERNET-DRAFT                                DSA Information in the DNS


   Copies of IPR disclosures made to the IETF Secretariat and any
   assurances of licenses to be made available, or the result of an
   attempt made to obtain a general license or permission for the use of
   such proprietary rights by implementers or users of this
   specification can be obtained from the IETF on-line IPR repository at
   http://www.ietf.org/ipr.

   The IETF invites any interested party to bring to its attention any
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   this standard.  Please address the information to the IETF at ietf-
   ipr@ietf.org.








































D. Eastlake 3rd                                                 [Page 8]


INTERNET-DRAFT                                DSA Information in the DNS


Normative References

   [FIPS186-2] - U.S. Federal Information Processing Standard: Digital
   Signature Standard, 27 January 2000.

   [RFC4034] - Arends, R., Austein, R., Larson, M., Massey, D., and S.
   Rose, "Resource Records for the DNS Security Extensions", RFC 4034,
   March 2005.



Informative References

   [FIPS180-2] - U.S. Federal Information Processing Standard: Secure
   Hash Standard, 1 August 2002.

   [RFC1034] - "Domain names - concepts and facilities", P. Mockapetris,
   11/01/1987.

   [RFC1035] - "Domain names - implementation and specification", P.
   Mockapetris, 11/01/1987.

   [RFC2536] - "DSA KEYs and SIGs in the Domain Name System (DNS)", D.
   Eastlake, March 1999.

   [RFC2671] - "Extension Mechanisms for DNS (EDNS0)", P. Vixie, August
   1999.

   [RFC2930] - Eastlake 3rd, D., "Secret Key Establishment for DNS (TKEY
   RR)", RFC 2930, September 2000.

   [RFC2931] - Eastlake 3rd, D., "DNS Request and Transaction Signatures
   ( SIG(0)s )", RFC 2931, September 2000.

   [RFC3110] - "RSA/SHA-1 SIGs and RSA KEYs in the Domain Name System
   (DNS)", D.  Eastlake 3rd. May 2001.

   [RFC3174] - "US Secure Hash Algorithm 1 (SHA1)", D. Eastlake, P.
   Jones, September 2001.

   [RFC3755] - Weiler, S., "Legacy Resolver Compatibility for Delegation
   Signer (DS)", May 2004.

   [RFC4025] - "A Method for Storing IPsec Keying Material in DNS", M.
   Richardson, March 2005.

   [RFC4033] - Arends, R., Austein, R., Larson, M., Massey, D., and S.
   Rose, "DNS Security Introduction and Requirements", RFC 4033, March
   2005.



D. Eastlake 3rd                                                 [Page 9]


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   [RFC4035] - Arends, R., Austein, R., Larson, M., Massey, D., and S.
   Rose, "Protocol Modifications for the DNS Security Extensions", RFC
   4035, March 2005.

   [RFC4086] - Eastlake, D., 3rd, Schiller, J., and S. Crocker,
   "Randomness Requirements for Security", BCP 106, RFC 4086, June 2005.

   [Schneier] - "Applied Cryptography Second Edition: protocols,
   algorithms, and source code in C" (second edition), Bruce Schneier,
   1996, John Wiley and Sons, ISBN 0-471-11709-9.










































D. Eastlake 3rd                                                [Page 10]


INTERNET-DRAFT                                DSA Information in the DNS


Author's Address

   Donald E. Eastlake 3rd
   Motorola Labortories
   155 Beaver Street
   Milford, MA 01757 USA

   Telephone:   +1-508-786-7554(w)
   EMail:       Donald.Eastlake@motorola.com



Expiration and File Name

   This draft expires in April 2007.

   Its file name is draft-ietf-dnsext-rfc2536bis-dsa-08.txt.



































D. Eastlake 3rd                                                [Page 11]


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