INTERNET-DRAFT Diffie-Hellman Keys in the DNS
May 1997
Expires November 1997
Storage of Diffie-Hellman Keys in the Domain Name System
------- -- -------------- ---- -- --- ------ ---- ------
Donald E. Eastlake 3rd
Status of This Document
This draft, file name draft-ietf-dnssec-dhk-00.txt, is intended to be
become a Proposed or Experimental Standard RFC. Distribution of this
document is unlimited. Comments should be sent to the DNS security
mailing list <dnssec@tis.com> or to the author.
This document is an Internet-Draft. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas,
and its working groups. Note that other groups may also distribute
working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six
months. Internet-Drafts may be updated, replaced, or obsoleted by
other documents at any time. It is not appropriate to use Internet-
Drafts as reference material or to cite them other than as a
``working draft'' or ``work in progress.''
To learn the current status of any Internet-Draft, please check the
1id-abstracts.txt listing contained in the Internet-Drafts Shadow
Directories on ds.internic.net (East USA), ftp.isi.edu (West USA),
nic.nordu.net (North Europe), ftp.nis.garr.it (South Europe),
munnari.oz.au (Pacific Rim), or ftp.is.co.za (Africa).
Donald E. Eastlake 3rd [Page 1]
INTERNET-DRAFT Diffie-Hellman Keys in the DNS
Abstract
A standard method for storing Diffie-Hellman keys in the Domain Name
System is described which utilizes DNS KEY resource records.
Acknowledgements
Part of the format for Diffie-Hellman keys and the description
thereof was taken from an Internet draft by:
Ashar Aziz <ashar.aziz@eng.sun.com>
Tom Markson <markson@incog.com>
Hemma Prafullchandra <hemma@eng.sun.com>
In addition, the following person provided useful comments that have
been incorporated:
Ran Atkinson <rja@inet.org>
Donald E. Eastlake 3rd [Page 2]
INTERNET-DRAFT Diffie-Hellman Keys in the DNS
Table of Contents
Status of This Document....................................1
Abstract...................................................2
Acknowledgements...........................................2
Table of Contents..........................................3
1. Introduction............................................4
2. Diffie-Hellman KEY Resource Records.....................5
3. Performance Considerations..............................6
4. Security Considerations.................................6
References.................................................7
Author's Address...........................................7
Expiration and File Name...................................7
Donald E. Eastlake 3rd [Page 3]
INTERNET-DRAFT Diffie-Hellman Keys in the DNS
1. Introduction
The Domain Name System (DNS) is the current global hierarchical
replicated distributed database system for Internet addressing, mail
proxy, and similar information. The DNS has recently been extended to
include digital signatures and cryptographic keys as described in RFC
2065. Thus the DNS can now be used for secure key distribution.
This document describes how to store Diffie-Hellman keys in the DNS.
Familiarity with the Diffie-Hellman key exchange algorithm is assumed
[Schneier].
Diffie-Hellman requires two parties to interact to derive keying
information which can then be used for authentication. Since DNS SIG
RRs are primarily used as quasi-static authenticators of zone
information for all resolvers, no Diffie-Hellman algorithm SIG RR is
defined.
Donald E. Eastlake 3rd [Page 4]
INTERNET-DRAFT Diffie-Hellman Keys in the DNS
2. Diffie-Hellman KEY Resource Records
Diffie-Hellman keys are stored in the DNS as KEY RRs using algorithm
number 2. The structure of the RDATA portion of this RR is as shown
below. The first 4 octets, including the flags, protocol, and
algorithm fields are common to all KEY RRs as described in RFC 2065.
The remainder, from prime length through public value is the "public
key" part of the KEY RR. 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 domain name.
1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| flags | protocol | algorithm=2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| prime length | prime (p) (variable length) /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ prime (p) (variable length) | generator length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| generator (g) (variable length) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| public value length | public value (variable length)/
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ public value (g^i mod p) (variable length) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
[Is it worth while defining some standard internet values for p and
g? That you are using them could be flagged by a zero or tiny "prime
length". Using such standard values would shorten the DH KEY RR a lot
but they might be tempting targets to break.]
Prime length is length of the Diffie-Hellman prime (p) in bytes.
Prime contains the binary representation of the Diffie-Hellman prime
with most significant byte first.
Generator length is the length of the generator (g) in bytes.
Generator is the binary representation of generator with most
significant byte first. PublicValueLen is the Length of the Public
Value (g^i mod p) in bytes. PublicValue is the binary representation
of the DH public value with most significant byte first.
The corresponding algorithm=2 SIG resource record is not used so no
format for it is defined.
Donald E. Eastlake 3rd [Page 5]
INTERNET-DRAFT Diffie-Hellman Keys in the DNS
3. Performance Considerations
Current DNS implementations are optimized for small transfers,
typically less than 512 bytes including overhead. While larger
transfers will perform correctly and work is underway to make larger
transfers more efficient, it is still advisable at this time to make
reasonable efforts to minimize the size of KEY RR sets stored within
the DNS consistent with adequate security. Keep in mind that in a
secure zone, an authenticating SIG RR will also be returned.
4. Security Considerations
Many of the security consideration in RFC 2065 apply. Of course, the
Diffie-Hellman key stored in the DNS for an entity should not be
trusted unless it has been obtain via a trusted DNS resolver that
vouches for its security or unless the application using the key has
done a similar authentication.
In addition, the usual Diffie-Hellman key strength considerations
apply. (p-1)/2 should also be prime, g should be primitive mod p, p
should be "large", etc. [Schneier]
Donald E. Eastlake 3rd [Page 6]
INTERNET-DRAFT Diffie-Hellman Keys in the DNS
References
[RFC 1034] - P. Mockapetris, "Domain names - concepts and
facilities", 11/01/1987.
[RFC 1035] - P. Mockapetris, "Domain names - implementation and
specification", 11/01/1987.
[RFC 2065] - Domain Name System Security Extensions, D. Eastlake, C.
Kaufman, January 1997.
[Schneier] - Bruce Schneier, "Applied Cryptography: Protocols,
Algorithms, and Source Code in C", 1996, John Wiley and Sons
Author's Address
Donald E. Eastlake 3rd
CyberCash, Inc.
318 Acton Street
Carlisle, MA 01741 USA
Telephone: +1 508 287 4877
+1 703 620-4200 (main office, Reston, VA)
FAX: +1 508 371 7148
EMail: dee@cybercash.com
Expiration and File Name
This draft expires in November 1997.
Its file name is draft-ietf-dnssec-dhk-00.txt.
Donald E. Eastlake 3rd [Page 7]
