Network Working Group J. Pawling
Request for Comments: 2876 WGSI, A Getronics Company
Category: Informational July 2000
Use of the KEA and SKIPJACK Algorithms in CMS
Status of this Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright (C) The Internet Society (2000). All Rights Reserved.
This document describes the conventions for using the Key Exchange
Algorithm (KEA) and SKIPJACK encryption algorithm in conjunction with
the Cryptographic Message Syntax [CMS] enveloped-data and encrypted-
data content types.
Throughout this document, the terms MUST, MUST NOT, SHOULD and MAY
are used in capital letters. This conforms to the definitions in
[MUSTSHOULD]. [MUSTSHOULD] defines the use of these key words to help
make the intent of standards track documents as clear as possible.
The same key words are used in this document to help implementers
achieve interoperability. Software that claims compliance with this
document MUST provide the capabilities as indicated by the MUST, MUST
NOT, SHOULD and MAY terms. The KEA and SKIPJACK cryptographic
algorithms are described in [SJ-KEA].
2. Content Encryption Process
This section applies to the construction of both the enveloped-data
and encrypted-data content types. Compliant software MUST meet the
requirements stated in [CMS] Section 6.3, "Content-encryption
Process". The input to the encryption process MUST be padded to a
multiple of eight octets using the padding rules described in [CMS]
Section 6.3. The content MUST be encrypted as a single string using
the SKIPJACK algorithm in 64-bit Cipher Block Chaining (CBC) mode
using randomly-generated 8-byte Initialization Vector (IV) and 80-bit
SKIPJACK content-encryption key (CEK) values.
Pawling Informational [Page 1]RFC 2876 KEA and SKIPJACK Algorithms in CMS July 20003. Content Decryption Process
This section applies to the processing of both the enveloped-data and
encrypted-data content types. The encryptedContent MUST be decrypted
as a single string using the SKIPJACK algorithm in 64-bit CBC mode.
The 80-bit SKIPJACK CEK and the 8-byte IV MUST be used as inputs to
the SKIPJACK decryption process. Following decryption, the padding
MUST be removed from the decrypted data. The padding rules are
described in [CMS] Section 6.3, "Content-encryption Process".
4. Enveloped-data Conventions
The CMS enveloped-data content type consists of an encrypted content
and wrapped CEKs for one or more recipients. Compliant software MUST
meet the requirements for constructing an enveloped-data content type
stated in [CMS] Section 6, "Enveloped-data Content Type". [CMS]
Section 6 should be studied before reading this section, because this
section does not repeat the [CMS] text.
An 8-byte IV and 80-bit CEK MUST be randomly generated for each
instance of an enveloped-data content type as inputs to the SKIPJACK
algorithm for use to encrypt the content. The SKIPJACK CEK MUST only
be used for encrypting the content of a single instance of an
enveloped-data content type.
KEA and SKIPJACK can be used with the enveloped-data content type
using either of the following key management techniques defined in
[CMS] Section 6:
1) Key Agreement: The SKIPJACK CEK is uniquely wrapped for each
recipient using a pairwise symmetric key-encryption key (KEK)
generated using KEA using the originator's private KEA key,
recipient's public KEA key and other values. Section 4.2 provides
2) "Previously Distributed" Symmetric KEK: The SKIPJACK CEK is
wrapped using a "previously distributed" symmetric KEK (such as a
Mail List Key). The methods by which the symmetric KEK is
generated and distributed are beyond the scope of this document.
Section 4.3 provides more details.
[CMS] Section 6 also defines the concept of the key transport key
management technique. The key transport technique MUST NOT be used
Pawling Informational [Page 2]RFC 2876 KEA and SKIPJACK Algorithms in CMS July 20004.1. EnvelopedData Fields
The enveloped-data content type is Abstract Syntax Notation.1 (ASN.1)