RFC 2984 (rfc2984) - Page 1 of 6

Use of the CAST-128 Encryption Algorithm in CMS

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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
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