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NetBSD/dist/bind/doc/draft/draft-ietf-dnsext-tsig-sha-00.txt
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INTERNET-DRAFT Donald E. Eastlake 3rd
UPDATES RFC 2845 Motorola Laboratories
Expires: February 2005 August 2004
HMAC SHA TSIG Algorithm Identifiers
---- --- ---- --------- -----------
<draft-ietf-dnsext-tsig-sha-00.txt>
Status of This Document
By submitting this Internet-Draft, I certify that any applicable
patent or other IPR claims of which I am aware have been disclosed,
or will be disclosed, and any of which I become aware will be
disclosed, in accordance with RFC 3668.
This draft is intended to be become a Proposed Standard RFC.
Distribution of this document is unlimited. Comments should be sent
to the DNSEXT working group mailing list <namedroppers@ops.ietf.org>.
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
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than a "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/1id-abstracts.html
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html
Abstract
Use of the TSIG DNS resource record requires specification of a
cryptographic message authentication code. Currently identifiers
have been specified only for the HMAC-MD5 and GSS TSIG algorithms.
This document standardizes identifiers for additional HMAC SHA TSIG
algorithms and standardizes how to specify the truncation of HMAC
values.
Copyright Notice
Copyright (C) The Internet Society 2004. All Rights Reserved.
D. Eastlake 3rd [Page 1]
INTERNET-DRAFT HMAC-SHA TSIG Identifiers
Table of Contents
Status of This Document....................................1
Abstract...................................................1
Copyright Notice...........................................1
Table of Contents..........................................2
1. Introduction............................................3
2. Algorithms and Identifiers..............................4
3. Specifying Truncation...................................5
4. IANA Considerations.....................................6
5. Security Considerations.................................6
6. Copyright and Disclaimer................................6
7. Normative References....................................7
8. Informative References..................................7
Authors Address............................................8
Expiration and File Name...................................8
D. Eastlake 3rd [Page 2]
INTERNET-DRAFT HMAC-SHA TSIG Identifiers
1. Introduction
[RFC 2845] specifies a TSIG Resource Record (RR) that can be used to
authenticate DNS queries and responses. This RR contains a domain
name syntax data item which names the authentication algorithm used.
[RFC 2845] defines the HMAC-MD5.SIG-ALG.REG.INT name for
authentication codes using the HMAC [RFC 2104] algorithm with the MD5
[RFC 1321] hash algorithm. IANA has also registered "gss-tsig" as an
identifier for TSIG authentication where the cryptographic operations
are delegated to GSS [RFC 3645].
In section 2, this document specifies additional names for TSIG
authentication algorithms based on US NIST SHA algorithms and HMAC.
In section 3, this document specifies the meaning of inequality
between the normal output size of the specified hash function and the
length of MAC (message authentication code) data given in the TSIG
RR. In particular, it specifies that a shorter length field value
specifies truncation and a longer length field is an error.
D. Eastlake 3rd [Page 3]
INTERNET-DRAFT HMAC-SHA TSIG Identifiers
2. Algorithms and Identifiers
TSIG Resource Records (RRs) [RFC 2845] are used to authenticate DNS
queries and responses. They are intended to be efficient symmetric
authentication codes based on a shared secret. (Asymmetric signatures
can be provided using the SIG RR [RFC 2931]. In particular, SIG(0)
can be used for transaction signatures.) Used with a strong hash
function, HMAC [RFC 2104] provides a way to calculate such symmetric
authentication codes. The only specified HMAC based TSIG algorithm
identifier has been HMAC-MD5.SIG-ALG.REG.INT based on MD5 [RFC 1321].
The use of SHA-1 [FIPS 180-1, RFC 3174], which is a 160 bit hash, as
compared with the 128 bits for MD5, and additional hash algorithms in
the SHA family [FIPS 180-2, RFC sha224] with 224, 256, 384, and 512
bits, may be preferred in some case. Use of TSIG between a DNS
resolver and server is by mutual agreement. That agreement can
include the support of additional algorithms.
For completeness in relation to HMAC based algorithms, the current
HMAC-MD5.SIG-ALG.REG.INT identifier is included in the table below.
Implementations which support TSIG MUST implement HMAC MD5, SHOULD
implement HMAC SHA-1, and MAY implement gss-tsig and the other
algorithms listed below.
Mandatory HMAC-MD5.SIG-ALG.REG.INT
Recommended hmac-sha1
Optional hmac-sha224
Optional hmac-sha256
Optional hamc-sha384
Optional hmac-sha512
D. Eastlake 3rd [Page 4]
INTERNET-DRAFT HMAC-SHA TSIG Identifiers
3. Specifying Truncation
In some cases, it is reasonable to truncate the output of HMAC and
use the truncated value for authentication. HMAC SHA-1 truncated to
96 bits is an optional available in several IETF protocols including
IPSEC and TLS.
The TSIG RR [RFC 2845] includes a "MAC size" field, which gives the
size of the MAC field in octets. But [RFC 2845] does not specify what
to do if this MAC size differs from the length of the output of HMAC
for a particular hash function.
The specification for TSIG handling is changed as follows:
1. If The "MAC size" field is larger than the HMAC output length or
is zero: This case MUST NOT be generated and if received MUST
cause the packet to be dropped and RCODE 1 (FORMERR) to be
returned.
2. If the "MAC size" field equals the HMAC output length: Operation
is as described in [RFC 2845].
3. If the "MAC size" field is less than the HMAC output length but is
not zero: This is sent when the signer has truncated the HMAC
output as described in RFC 2104, taking initial octets and
discarding trailing octets. TSIG truncation can only be to an
integral number of octets. On receipt of a packet with truncation
thus indicated, the locally calculated MAC is similarly truncated
and only the truncated values compared for authentication.
TSIG implementations SHOULD implement SHA-1 truncated to 96 bits (12
octets) and MAY implement any or all other truncations valid under
case 3 above.
D. Eastlake 3rd [Page 5]
INTERNET-DRAFT HMAC-SHA TSIG Identifiers
4. IANA Considerations
This document, on approval for publication as a standards track RFC,
registers the new TSIG algorithm identifiers listed in Section 2 with
IANA.
5. Security Considerations
For all of the message authentication code algorithms listed herein,
those producing longer values are believed to be stronger; however,
while there are some arguments that mild truncation can strengthen a
MAC by reducing the information available to an attacker, excessive
truncation clearly weakens authentication by reducing the number of
bits an attacker has to try to force. See [RFC 2104] which recommends
that ah HMAC never be truncated to less than half its length nor to
less than 80 bits (10 octets).
See also the Security Considerations section of [RFC 2845].
6. Copyright and Disclaimer
Copyright (C) The Internet Society 2004. 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.
D. Eastlake 3rd [Page 6]
INTERNET-DRAFT HMAC-SHA TSIG Identifiers
7. Normative References
[FIPS 180-2] - "Secure Hash Standard", (SHA-1/256/384/512) US Federal
Information Processing Standard, Draft, 1 August 2002.
[RFC 1321] - Rivest, R., "The MD5 Message-Digest Algorithm ", RFC
1321, April 1992.
[RFC 2104] - Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
Hashing for Message Authentication", RFC 2104, February 1997.
[RFC 2434] - Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 2434, October 1998.
[RFC 2845] - Vixie, P., Gudmundsson, O., Eastlake 3rd, D., and B.
Wellington, "Secret Key Transaction Authentication for DNS (TSIG)",
RFC 2845, May 2000.
[RFC sha224] - "A 224-bit One-way Hash Function: SHA-224", R.
Housley, December 2003, work in progress, draft-ietf-pkix-
sha224-*.txt.
8. Informative References.
[FIPS 180-1] - Secure Hash Standard, (SHA-1) US Federal Information
Processing Standard, 17 April 1995.
[RFC 2931] - Eastlake 3rd, D., "DNS Request and Transaction
Signatures ( SIG(0)s )", RFC 2931, September 2000.
[RFC 3174] - Eastlake 3rd, D. and P. Jones, "US Secure Hash Algorithm
1 (SHA1)", RFC 3174, September 2001.
[RFC 3645] - Kwan, S., Garg, P., Gilroy, J., Esibov, L., Westhead,
J., and R. Hall, "Generic Security Service Algorithm for Secret Key
Transaction Authentication for DNS (GSS-TSIG)", RFC 3645, October
2003.
D. Eastlake 3rd [Page 7]
INTERNET-DRAFT HMAC-SHA TSIG Identifiers
Authors Address
Donald E. Eastlake 3rd
Motorola Laboratories
155 Beaver Street
Milford, MA 01757 USA
Telephone: +1-508-786-7554 (w)
+1-508-634-2066 (h)
EMail: Donald.Eastlake@motorola.com
Expiration and File Name
This draft expires in February 2005.
Its file name is draft-ietf-dnsext-tsig-sha-00.txt
D. Eastlake 3rd [Page 8]
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