2 INTERNET-DRAFT DSA Information in the DNS
3 OBSOLETES: RFC 2536 Donald E. Eastlake 3rd
5 Expires: January 2006 July 2005
8 DSA Keying and Signature Information in the DNS
9 --- ------ --- --------- ----------- -- --- ---
10 <draft-ietf-dnsext-rfc2536bis-dsa-06.txt>
11 Donald E. Eastlake 3rd
14 Status of This Document
16 By submitting this Internet-Draft, each author represents that any
17 applicable patent or other IPR claims of which he or she is aware
18 have been or will be disclosed, and any of which he or she becomes
19 aware will be disclosed, in accordance with Section 6 of BCP 79.
21 Distribution of this document is unlimited. Comments should be sent
22 to the DNS extensions working group mailing list
23 <namedroppers@ops.ietf.org>.
25 Internet-Drafts are working documents of the Internet Engineering
26 Task Force (IETF), its areas, and its working groups. Note that
27 other groups may also distribute working documents as Internet-
30 Internet-Drafts are draft documents valid for a maximum of six months
31 and may be updated, replaced, or obsoleted by other documents at any
32 time. It is inappropriate to use Internet-Drafts as reference
33 material or to cite them other than a "work in progress."
35 The list of current Internet-Drafts can be accessed at
36 http://www.ietf.org/1id-abstracts.html
38 The list of Internet-Draft Shadow Directories can be accessed at
39 http://www.ietf.org/shadow.html
44 The standard method of encoding US Government Digital Signature
45 Algorithm keying and signature information for use in the Domain Name
51 Copyright (C) The Internet Society 2005. All Rights Reserved.
57 D. Eastlake 3rd [Page 1]
60 INTERNET-DRAFT DSA Information in the DNS
65 Status of This Document....................................1
66 Abstract...................................................1
67 Copyright Notice...........................................1
69 Table of Contents..........................................2
71 1. Introduction............................................3
72 2. DSA Keying Information..................................3
73 3. DSA Signature Information...............................4
74 4. Performance Considerations..............................4
75 5. Security Considerations.................................5
76 6. IANA Considerations.....................................5
77 Copyright and Disclaimer...................................5
79 Normative References.......................................7
80 Informative References.....................................7
82 Authors Address............................................8
83 Expiration and File Name...................................8
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118 INTERNET-DRAFT DSA Information in the DNS
123 The Domain Name System (DNS) is the global hierarchical replicated
124 distributed database system for Internet addressing, mail proxy, and
125 other information [RFC 1034, 1035]. The DNS has been extended to
126 include digital signatures and cryptographic keys as described in
127 [RFC 4033, 4034, 4035] and additional work is underway which would
128 require the storage of keying and signature information in the DNS.
130 This document describes how to encode US Government Digital Signature
131 Algorithm (DSA) keys and signatures in the DNS. Familiarity with the
132 US Digital Signature Algorithm is assumed [FIPS 186-2, Schneier].
136 2. DSA Keying Information
138 When DSA public keys are stored in the DNS, the structure of the
139 relevant part of the RDATA part of the RR being used is the fields
140 listed below in the order given.
142 The period of key validity is not included in this data but is
143 indicated separately, for example by an RR such as RRSIG which signs
144 and authenticates the RR containing the keying information.
154 As described in [FIPS 186-2] and [Schneier], T is a key size
155 parameter chosen such that 0 <= T <= 8. (The meaning if the T octet
156 is greater than 8 is reserved and the remainder of the data may have
157 a different format in that case.) Q is a prime number selected at
158 key generation time such that 2**159 < Q < 2**160. Thus Q is always
159 20 octets long and, as with all other fields, is stored in "big-
160 endian" network order. P, G, and Y are calculated as directed by the
161 [FIPS 186-2] key generation algorithm [Schneier]. P is in the range
162 2**(511+64T) < P < 2**(512+64T) and thus is 64 + 8*T octets long. G
163 and Y are quantities modulo P and so can be up to the same length as
164 P and are allocated fixed size fields with the same number of octets
167 During the key generation process, a random number X must be
168 generated such that 1 <= X <= Q-1. X is the private key and is used
169 in the final step of public key generation where Y is computed as
173 D. Eastlake 3rd [Page 3]
176 INTERNET-DRAFT DSA Information in the DNS
183 3. DSA Signature Information
185 The portion of the RDATA area used for US Digital Signature Algorithm
186 signature information is shown below with fields in the order they
187 are listed and the contents of each multi-octet field in "big-endian"
196 First, the data signed must be determined. Then the following steps
197 are taken, as specified in [FIPS 186-2], where Q, P, G, and Y are as
198 specified in the public key [Schneier]:
200 hash = SHA-1 ( data )
202 Generate a random K such that 0 < K < Q.
204 R = ( G**K mod P ) mod Q
206 S = ( K**(-1) * (hash + X*R) ) mod Q
208 For information on the SHA-1 hash function see [FIPS 180-2] and [RFC
211 Since Q is 160 bits long, R and S can not be larger than 20 octets,
212 which is the space allocated.
214 T is copied from the public key. It is not logically necessary in
215 the SIG but is present so that values of T > 8 can more conveniently
216 be used as an escape for extended versions of DSA or other algorithms
217 as later standardized.
221 4. Performance Considerations
223 General signature generation speeds are roughly the same for RSA [RFC
224 3110] and DSA. With sufficient pre-computation, signature generation
225 with DSA is faster than RSA. Key generation is also faster for DSA.
226 However, signature verification is an order of magnitude slower than
227 RSA when the RSA public exponent is chosen to be small, as is
228 recommended for some applications.
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234 INTERNET-DRAFT DSA Information in the DNS
237 Current DNS implementations are optimized for small transfers,
238 typically less than 512 bytes including DNS overhead. Larger
239 transfers will perform correctly and extensions have been
240 standardized [RFC 2671] to make larger transfers more efficient, it
241 is still advisable at this time to make reasonable efforts to
242 minimize the size of RR sets containing keying and/or signature
243 inforamtion consistent with adequate security.
247 5. Security Considerations
249 Keys retrieved from the DNS should not be trusted unless (1) they
250 have been securely obtained from a secure resolver or independently
251 verified by the user and (2) this secure resolver and secure
252 obtainment or independent verification conform to security policies
253 acceptable to the user. As with all cryptographic algorithms,
254 evaluating the necessary strength of the key is essential and
255 dependent on local policy.
257 The key size limitation of a maximum of 1024 bits ( T = 8 ) in the
258 current DSA standard may limit the security of DSA. For particular
259 applications, implementors are encouraged to consider the range of
260 available algorithms and key sizes.
262 DSA assumes the ability to frequently generate high quality random
263 numbers. See [random] for guidance. DSA is designed so that if
264 biased rather than random numbers are used, high bandwidth covert
265 channels are possible. See [Schneier] and more recent research. The
266 leakage of an entire DSA private key in only two DSA signatures has
267 been demonstrated. DSA provides security only if trusted
268 implementations, including trusted random number generation, are
273 6. IANA Considerations
275 Allocation of meaning to values of the T parameter that are not
276 defined herein (i.e., > 8 ) requires an IETF standards actions. It
277 is intended that values unallocated herein be used to cover future
278 extensions of the DSS standard.
282 Copyright and Disclaimer
284 Copyright (C) The Internet Society (2005). This document is subject to
285 the rights, licenses and restrictions contained in BCP 78, and except
286 as set forth therein, the authors retain all their rights.
289 D. Eastlake 3rd [Page 5]
292 INTERNET-DRAFT DSA Information in the DNS
295 This document and the information contained herein are provided on an
296 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
297 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
298 ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
299 INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
300 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
301 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
347 D. Eastlake 3rd [Page 6]
350 INTERNET-DRAFT DSA Information in the DNS
355 [FIPS 186-2] - U.S. Federal Information Processing Standard: Digital
356 Signature Standard, 27 January 2000.
358 [RFC 4034] - Arends, R., Austein, R., Larson, M., Massey, D., and S.
359 Rose, "Resource Records for the DNS Security Extensions", RFC 4034,
364 Informative References
366 [RFC 1034] - "Domain names - concepts and facilities", P.
367 Mockapetris, 11/01/1987.
369 [RFC 1035] - "Domain names - implementation and specification", P.
370 Mockapetris, 11/01/1987.
372 [RFC 2671] - "Extension Mechanisms for DNS (EDNS0)", P. Vixie, August
375 [RFC 3110] - "RSA/SHA-1 SIGs and RSA KEYs in the Domain Name System
376 (DNS)", D. Eastlake 3rd. May 2001.
378 [RFC 3174] - "US Secure Hash Algorithm 1 (SHA1)", D. Eastlake, P.
379 Jones, September 2001.
381 [RFC 4033] - Arends, R., Austein, R., Larson, M., Massey, D., and S.
382 Rose, "DNS Security Introduction and Requirements", RFC 4033, March
385 [RFC 4035] - Arends, R., Austein, R., Larson, M., Massey, D., and S.
386 Rose, "Protocol Modifications for the DNS Security Extensions", RFC
389 [RFC 4086] - Eastlake, D., 3rd, Schiller, J., and S. Crocker,
390 "Randomness Requirements for Security", BCP 106, RFC 4086, June 2005.
392 [Schneier] - "Applied Cryptography Second Edition: protocols,
393 algorithms, and source code in C" (second edition), Bruce Schneier,
394 1996, John Wiley and Sons, ISBN 0-471-11709-9.
405 D. Eastlake 3rd [Page 7]
408 INTERNET-DRAFT DSA Information in the DNS
413 Donald E. Eastlake 3rd
416 Milford, MA 01757 USA
418 Telephone: +1-508-786-7554(w)
419 EMail: Donald.Eastlake@motorola.com
423 Expiration and File Name
425 This draft expires in January 2006.
427 Its file name is draft-ietf-dnsext-rfc2536bis-dsa-06.txt.
463 D. Eastlake 3rd [Page 8]