< draft-ietf-dnssec-dss-02.txt   draft-ietf-dnssec-dss-03.txt >
INTERNET-DRAFT DSA KEYs and SIGs in the DNS INTERNET-DRAFT DSA KEYs and SIGs in the DNS
January 1998 October 1998
Expires July 1998 Expires April 1999
DSA KEYs and SIGs in the Domain Name System (DNS) DSA KEYs and SIGs in the Domain Name System (DNS)
--- ---- --- ---- -- --- ------ ---- ------ ----- --- ---- --- ---- -- --- ------ ---- ------ -----
Donald E. Eastlake 3rd Donald E. Eastlake 3rd
Status of This Document Status of This Document
This draft, file name draft-ietf-dnssec-dss-02.txt, is intended to be This draft, file name draft-ietf-dnssec-dss-03.txt, is intended to be
become a Proposed Standard RFC. Distribution of this document is become a Proposed Standard RFC. Distribution of this document is
unlimited. Comments should be sent to the DNS security mailing list unlimited. Comments should be sent to the DNS security mailing list
<dns-security@tis.com> or to the author. <dns-security@tis.com> or to the author.
This document is an Internet-Draft. Internet-Drafts are working This document is an Internet-Draft. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas, documents of the Internet Engineering Task Force (IETF), its areas,
and its working groups. Note that other groups may also distribute and its working groups. Note that other groups may also distribute
working documents as Internet-Drafts. working documents as Internet-Drafts.
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[Changes from previous draft: change dates, update author info, add
IANA Considerations]
Abstract Abstract
A standard method for storing US Government Digital Signature A standard method for storing US Government Digital Signature
Algorithm keys and signatures in the Domain Name System is described Algorithm keys and signatures in the Domain Name System is described
which utilizes DNS KEY and SIG resource records. which utilizes DNS KEY and SIG resource records.
INTERNET-DRAFT DSA in the DNS INTERNET-DRAFT DSA in the DNS
Table of Contents Table of Contents
Status of This Document....................................1 Status of This Document....................................1
Abstract...................................................1 Abstract...................................................1
Table of Contents..........................................2 Table of Contents..........................................2
1. Introduction............................................3 1. Introduction............................................3
2. DSA KEY Resource Records................................3
3. DSA SIG Resource Records................................4
4. Performance Considerations..............................4
5. Security Considerations.................................5
6. IANA Considerations.....................................5
2. DSA KEY Resource Records................................4 References.................................................6
Author's Address...........................................6
3. DSA SIG Resource Records................................5 Expiration and File Name...................................6
4. Performance Considerations..............................6
5. Security Considerations.................................6
References.................................................7
Author's Address...........................................7
Expiration and File Name...................................7
INTERNET-DRAFT DSA in the DNS INTERNET-DRAFT DSA in the DNS
1. Introduction 1. Introduction
The Domain Name System (DNS) is the global hierarchical replicated The Domain Name System (DNS) is the global hierarchical replicated
distributed database system for Internet addressing, mail proxy, and distributed database system for Internet addressing, mail proxy, and
other information. The DNS has been extended to include digital other information. The DNS has been extended to include digital
signatures and cryptographic keys as described in [draft-ietf- signatures and cryptographic keys as described in [draft-ietf-
dnssec-secext2-*]. Thus the DNS can now be secured and can be used dnssec-secext2-*]. Thus the DNS can now be secured and can be used
for secure key distribution. for secure key distribution.
This document describes how to store US Government Digital Signature This document describes how to store US Government Digital Signature
Algorithm (DSA) keys and signatures in the DNS. Familiarity with the Algorithm (DSA) keys and signatures in the DNS. Familiarity with the
US Digital Signature Algorithm is assumed [Schneier]. Implementation US Digital Signature Algorithm is assumed [Schneier]. Implementation
of DSA is mandatory for DNS security. of DSA is mandatory for DNS security.
INTERNET-DRAFT DSA in the DNS
2. DSA KEY Resource Records 2. DSA KEY Resource Records
DSA public keys are stored in the DNS as KEY RRs using algorithm DSA public keys are stored in the DNS as KEY RRs using algorithm
number 3 [draft-ietf-dnssec-secext2-*]. The structure of the number 3 [draft-ietf-dnssec-secext2-*]. The structure of the
algorithm specific portion of the RDATA part of this RR is as shown 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 below. These fields, from Q through Y are the "public key" part of
the DSA KEY RR. the DSA KEY RR.
The period of key validity is not in the KEY RR but is indicated by 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 the SIG RR(s) which signs and authenticates the KEY RR(s) at that
skipping to change at page 4, line 41 skipping to change at page 4, line 4
number selected at key generation time such that 2**159 < Q < 2**160 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 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 stored in "big-endian" network order. P, G, and Y are calculated as
directed by the FIPS 186 key generation algorithm [Schneier]. P is 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 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 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 the same length as P and are allocated fixed size fields with the
same number of octets as P. same number of octets as P.
During the key generation process, a random number X must be During the key generation process, a random number X must be
INTERNET-DRAFT DSA in the DNS
generated such that 1 <= X <= Q-1. X is the private key and is used 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 in the final step of public key generation where Y is computed as
Y = G**X mod P Y = G**X mod P
INTERNET-DRAFT DSA in the DNS
3. DSA SIG Resource Records 3. DSA SIG Resource Records
The signature portion of the SIG RR RDATA area, when using the US The signature portion of the SIG RR RDATA area, when using the US
Digital Signature Algorithm, is shown below with fields in the order Digital Signature Algorithm, is shown below with fields in the order
they occur. See [draft-ietf-dnssec-secext2-*] for fields in the SIG they occur. See [draft-ietf-dnssec-secext2-*] for fields in the SIG
RR RDATA which precede the signature itself. RR RDATA which precede the signature itself.
Field Size Field Size
----- ---- ----- ----
T 1 octet T 1 octet
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S = ( K**(-1) * (hash + X*R) ) mod Q S = ( K**(-1) * (hash + X*R) ) mod Q
Since Q is 160 bits long, R and S can not be larger than 20 octets, Since Q is 160 bits long, R and S can not be larger than 20 octets,
which is the space allocated. which is the space allocated.
T is copied from the public key. It is not logically necessary in T is copied from the public key. It is not logically necessary in
the SIG but is present so that values of T > 8 can more conveniently the SIG 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 be used as an escape for extended versions of DSA or other algorithms
as later specified. as later specified.
INTERNET-DRAFT DSA in the DNS
4. Performance Considerations 4. Performance Considerations
General signature generation speeds are roughly the same for RSA [RFC General signature generation speeds are roughly the same for RSA [RFC
xRSA] and DSA. With sufficient pre-computation, signature generation xRSA] and DSA. With sufficient pre-computation, signature generation
with DSA is faster than RSA. Key generation is also faster for DSA. with DSA is faster than RSA. Key generation is also faster for DSA.
However, signature verification is an order of magnitude slower than However, signature verification is an order of magnitude slower than
RSA when the RSA public exponent is chosen to be small as is RSA when the RSA public exponent is chosen to be small as is
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recommended for KEY RRs used in domain name system (DNS) data recommended for KEY RRs used in domain name system (DNS) data
authentication. authentication.
Current DNS implementations are optimized for small transfers, Current DNS implementations are optimized for small transfers,
typically less than 512 bytes including overhead. While larger typically less than 512 bytes including overhead. While larger
transfers will perform correctly and work is underway to make larger transfers will perform correctly and work is underway to make larger
transfers more efficient, it is still advisable at this time to make transfers more efficient, it is still advisable at this time to make
reasonable efforts to minimize the size of KEY RR sets stored within reasonable efforts to minimize the size of KEY RR sets stored within
the DNS consistent with adequate security. Keep in mind that in a the DNS consistent with adequate security. Keep in mind that in a
secure zone, at least one authenticating SIG RR will also be secure zone, at least one authenticating SIG RR will also be
skipping to change at page 7, line 5 skipping to change at page 5, line 44
DSA assumes the ability to frequently generate high quality random DSA assumes the ability to frequently generate high quality random
numbers. See [RFC 1750] for guidance. DSA is designed so that if numbers. See [RFC 1750] for guidance. DSA is designed so that if
manipulated rather than random numbers are used, very high bandwidth manipulated rather than random numbers are used, very high bandwidth
covert channels are possible. See [Schneier] and more recent covert channels are possible. See [Schneier] and more recent
research. The leakage of an entire DSA private key in only two DSA research. The leakage of an entire DSA private key in only two DSA
signatures has been demonstrated. DSA provides security only if signatures has been demonstrated. DSA provides security only if
trusted implementations, including trusted random number generation, trusted implementations, including trusted random number generation,
are used. are used.
6. IANA Considerations
Allocation of meaning to values of the T parameter that are not
defined herein requires an IETF standards actions. It is intended
that values unallocated herein be used to cover future extensions of
the DSS standard.
INTERNET-DRAFT DSA in the DNS INTERNET-DRAFT DSA in the DNS
References References
[FIPS 186] - U.S. Federal Information Processing Standard: Digital [FIPS 186] - U.S. Federal Information Processing Standard: Digital
Signature Standard. Signature Standard.
[RFC 1034] - P. Mockapetris, "Domain names - concepts and [RFC 1034] - P. Mockapetris, "Domain names - concepts and
facilities", 11/01/1987. facilities", 11/01/1987.
[RFC 1035] - P. Mockapetris, "Domain names - implementation and [RFC 1035] - P. Mockapetris, "Domain names - implementation and
specification", 11/01/1987. specification", 11/01/1987.
[RFC 1750] - D. Eastlake, S. Crocker, J. Schiller, "Randomness [RFC 1750] - D. Eastlake, S. Crocker, J. Schiller, "Randomness
Recommendations for Security", 12/29/1994. Recommendations for Security", 12/29/1994.
[draft-ietf-dnssec-secext2-*] - Domain Name System Security [draft-ietf-dnssec-secext2-*] - Domain Name System Security
Extensions, D. Eastlake, C. Kaufman, January 1997. Extensions, D. Eastlake, C. Kaufman, January 1997.
[RFC xRSA] - draft-ietf-dnssec-rsa-*.txt [RFC xRSA] - draft-ietf-dnssec-rsa-*.txt - RSA/MD5 KEYs and SIGs in
the Domain Name System (DNS), D. Eastlake.
[Schneier] - Bruce Schneier, "Applied Cryptography Second Edition: [Schneier] - Bruce Schneier, "Applied Cryptography Second Edition:
protocols, algorithms, and source code in C", 1996, John Wiley and protocols, algorithms, and source code in C", 1996, John Wiley and
Sons, ISBN 0-471-11709-9. Sons, ISBN 0-471-11709-9.
Author's Address Author's Address
Donald E. Eastlake 3rd Donald E. Eastlake 3rd
CyberCash, Inc. IBM
318 Acton Street 318 Acton Street
Carlisle, MA 01741 USA Carlisle, MA 01741 USA
Telephone: +1 978 287 4877 Telephone: +1-978-287-4877
+1 703 620-4200 (main office, Reston, Virginia) +1-914-784-7913
FAX: +1 978 371 7148 FAX: +1-978-371-7148
EMail: dee@cybercash.com EMail: dee3@us.ibm.com
Expiration and File Name Expiration and File Name
This draft expires in July 1998. This draft expires in April 1999.
Its file name is draft-ietf-dnssec-dss-02.txt. Its file name is draft-ietf-dnssec-dss-03.txt.
 End of changes. 16 change blocks. 
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