Network Working Group D. Eastlake 3rd
Request for Comments: 4635 Motorola Laboratories
Category: Standards Track August 2006
HMAC SHA TSIG Algorithm Identifiers
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
Use of the Domain Name System TSIG resource record requires
specification of a cryptographic message authentication code.
Currently, identifiers have been specified only for HMAC MD5 (Hashed
Message Authentication Code, Message Digest 5) and GSS (Generic
Security Service) TSIG algorithms. This document standardizes
identifiers and implementation requirements for additional HMAC SHA
(Secure Hash Algorithm) TSIG algorithms and standardizes how to
specify and handle the truncation of HMAC values in TSIG.
Table of Contents
1. Introduction ....................................................2
2. Algorithms and Identifiers ......................................2
3. Specifying Truncation ...........................................3
3.1. Truncation Specification ...................................4
4. TSIG Truncation Policy and Error Provisions .....................4
5. IANA Considerations .............................................5
6. Security Considerations .........................................5
7. Normative References ............................................6
8. Informative References. .........................................7
Eastlake 3rd Standards Track [Page 1]
RFC 4635 HMAC SHA TSIG Algorithm Identifiers August 2006
1. Introduction
[RFC2845] specifies a TSIG Resource Record (RR) that can be used to
authenticate DNS (Domain Name System [STD13]) queries and responses.
This RR contains a domain name syntax data item that names the
authentication algorithm used. [RFC2845] defines the
HMAC-MD5.SIG-ALG.REG.INT name for authentication codes using the HMAC
(Hashed Message Authentication Code) [RFC2104] algorithm with the MD5
(Message Digest 5) [RFC1321] hash algorithm. IANA has also
registered "gss-tsig" as an identifier for TSIG authentication where
the cryptographic operations are delegated to the Generic Security
Service (GSS) [RFC3645].
Note that use of TSIG presumes prior agreement, between the resolver
and server involved, as to the algorithm and key to be used.
In Section 2, this document specifies additional names for TSIG
authentication algorithms based on US NIST SHA (United States,
National Institute of Science and Technology, Secure Hash Algorithm)
algorithms and HMAC and specifies the implementation requirements for
those algorithms.
In Section 3, this document specifies the effect 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 that a longer-length field is an error.
In Section 4, policy restrictions and implications related to
truncation are described and specified, as is a new error code to
indicate truncation shorter than that permitted by policy.
The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", "MAY", in
this document are to be interpreted as described in [RFC2119].
2. Algorithms and Identifiers
TSIG Resource Records (RRs) [RFC2845] 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 [RFC2931]. In
particular, SIG(0) can be used for transaction signatures.) Used
with a strong hash function, HMAC [RFC2104] 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 [RFC1321].
Eastlake 3rd Standards Track [Page 2]
RFC 4635 HMAC SHA TSIG Algorithm Identifiers August 2006
The use of SHA-1 [FIPS180-2, RFC3174], which is a 160-bit hash, as
datatracker.ietf.org