Use of the CAST-128 Encryption Algorithm in CMS (RFC2984)
Original Publication Date: 2000-Oct-01
Included in the Prior Art Database: 2019-Feb-12
Internet Society Requests For Comment (RFCs)
This document specifies how to incorporate CAST-128 into the S/MIME Cryptographic Message Syntax (CMS) as an additional algorithm for symmetric encryption. [STANDARDS-TRACK]
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 (C) The Internet Society (2000). All Rights Reserved.
This document specifies how to incorporate CAST-128 (RFC2144) 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 (RFC2630) 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 [RFC2119].
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 [RFC2144, 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 [Page 1]
RFC 2984 CAST-128 in CMS October 2000
commercial and non-commercial uses worldwide [IPR], and therefore is widely used in a number of applications around the Internet. It thus seems to be a suitable optional encryption algorithm for S/MIME.
This document describes how to use CAST-128 within the S/MIME CMS specification.
This section provides the OIDs and processing information necessary for CAST-128 to be used for content and key encryption in CMS.
2.1 OIDs for Content and Key Encryption
CAST-128 is added to the set of optional symmetric encryption algorithms in CMS by providing two unique object identifiers (OIDs). One OID defines the content encryption algorithm and the other defines the key encryption algorithm. Thus a CMS agent can apply CAST-128 either for content or key encryption by selecting the corresponding object identifier, supplying the required parameter, and starting...