RFC 2984 (rfc2984) - Page 1 of 6
Use of the CAST-128 Encryption Algorithm in CMS
Alternative Format: Original Text Document
Network Working Group C. Adams
Request for Comments: 2984 Entrust Technologies
Category: Standards Track October 2000
Use of the CAST-128 Encryption Algorithm in CMS
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 (2000). All Rights Reserved.
Abstract
This document specifies how to incorporate CAST-128 (RFC 2144) into
the S/MIME Cryptographic Message Syntax (CMS) as an additional
algorithm for symmetric encryption. The relevant OIDs and processing
steps are provided so that CAST-128 may be included in the CMS
specification (RFC 2630) for symmetric content and key encryption.
The key words "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT",
"RECOMMENDED", "MAY", and "OPTIONAL" in this document (in uppercase,
as shown) are to be interpreted as described in [RFC 2119].
1. Motivation
S/MIME (Secure/Multipurpose Internet Mail Extensions) [SMIME2,
SMIME3] is a set of specifications for the secure transport of MIME
objects. In the current (S/MIME v3) specifications the mandatory-
to-implement symmetric algorithm for content encryption and key
encryption is triple-DES (3DES). While this is perfectly acceptable
in many cases because the security of 3DES is generally considered to
be high, for some environments 3DES may be seen to be too slow. In
part to help alleviate such performance concerns, S/MIME has allowed
any number of (optional) additional algorithms to be used for
symmetric content and key encryption.
The CAST-128 encryption algorithm [RFC 2144, Adams] is a well-studied
symmetric cipher that has a number of appealing features, including
relatively high performance and a variable key size (from 40 bits to
128 bits). It is available royalty-free and license-free for
Adams Standards Track