rfc3058.txt

最新的RFC

Network Working Group                                          S. Teiwes
Request for Comments: 3058                                   P. Hartmann
Category:Informational                             iT_Security AG (Ltd.)
                                                               D. Kuenzi
                                                      724 Solutions Inc.
                                                           February 2001


              Use of the IDEA Encryption Algorithm 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 Notice

   Copyright (C) The Internet Society (2001).  All Rights Reserved.

Abstract

   This memo specifies how to incorporate International Data Encryption
   Algorithm (IDEA) into CMS or S/MIME as an additional strong algorithm
   for symmetric encryption.  For organizations who make use of IDEA for
   data security purposes it is of high interest that IDEA is also
   available in S/MIME.  The intention of this memo is to provide the
   OIDs and algorithms required that IDEA can be included in S/MIME for
   symmetric content and key encryption.

1. Introduction

   This memo specifies how to incorporate International Data Encryption
   Algorithm (IDEA) [IDEA] into CMS or S/MIME [SMIME2, SMIME3] as an
   additional strong algorithm for symmetric encryption.  For
   organizations who make use of IDEA for data security purposes it is
   of high interest that IDEA is also available in S/MIME.  The
   intention of this memo is to provide the OIDs and algorithms required
   that IDEA can be included in S/MIME for symmetric content and key
   encryption.

   The general functional capabilities and preferences of S/MIME are
   specified by the registered list of S/MIME object identifiers (OIDs).
   This list of OIDs is available from the Internet Mail Consortium at
   <http://www.imc.org/ietf-smime/oids.html>.  The set of S/MIME
   functions provided by a client is expressed by the S/MIME
   capabilities attribute.  This attribute contains a list of OIDs of
   supported cryptographic functions.



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RFC 3058            IDEA Encryption Algorithm in CMS       February 2001


   In this document, the terms MUST, MUST NOT, SHOULD, and SHOULD NOT
   are used in capital letters.  This conforms to the definitions in
   [MUSTSHOULD].

2. Object Identifier for Content and Key Encryption

   The Cryptographic Message Syntax [CMS], derived from PKCS#7 [PKCS7],
   is the framework for the implementation of cryptographic functions in
   S/MIME.  It specifies data formats and encryption processes without
   naming the cryptographic algorithms.  Each algorithm which is used
   for encryption purposes must be specified by a unique algorithm
   identifier.  For example, in the special case of content encryption
   the ContentEncryptionAlgorithmIdentifier specifies the algorithm to
   be applied.  However, according to [CMS] any symmetric encryption
   algorithm that a CMS implementation includes as a content-encryption
   algorithm must also be included as a key-encryption algorithm.

   IDEA is added to the set of optional symmetric encryption algorithms
   in S/MIME by providing two unique object identifiers (OIDs).  One OID
   defines content encryption and the other one key encryption.  Thus an
   S/MIME agent can apply IDEA either for content or key encryption by
   selecting the corresponding object identifier, supplying the required
   parameter, and starting the program code.

   For content encryption the use of IDEA in cipher block chaining (CBC)
   mode is recommended.  The key length is fixed to 128 bits.

   The IDEA content-encryption algorithm in CBC mode has the object
   identifier

     IDEA-CBC OBJECT IDENTIFIER
       ::= { iso(1) identified-organization(3)
           usdod(6) oid(1) private(4) enterprises(1)
           ascom(188) systec(7) security(1) algorithms(1) 2 }

   The identifier's parameters field contains the initialization vector
   (IV) as an optional parameter.

     IDEA-CBCPar ::= SEQUENCE {
       iv  OCTET STRING OPTIONAL } -- exactly 8 octets

   If IV is specified as above, it MUST be used as initial vector.  In
   this case, the ciphertext MUST NOT include the initial vector.  If IV
   is not specified, the first 64 bits of the ciphertext MUST be
   considered as the initial vector.  However, this alternative of not
   including IV into "iv OCTET STRING" of IDEA-CBCPar SHOULD NOT be
   applied in CMS or S/MIME.




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RFC 3058            IDEA Encryption Algorithm in CMS       February 2001


   The key-wrap/unwrap algorithms used to encrypt/decrypt an IDEA
   content-encryption key with an IDEA key-encryption key are specified
   in the following section.  Generation and distribution of IDEA key-
   encryption keys are beyond the scope of this document.

   The IDEA key-encryption algorithm has the object identifier

     id-alg-CMSIDEAwrap OBJECT IDENTIFIER
       ::= { iso(1) identified-organization(3)
           usdod(6) oid(1) private(4) enterprises(1)
           ascom(188) systec(7) security(1) algorithms(1) 6 }

   The identifier's parameters field MUST be NULL.

3. Key-Wrapping and Unwrapping

   In the following subsections IDEA key-wrap and key-unwrap algorithms
   are specified in conformance with [CMS], section 12.3.

3.1 IDEA Key Wrap

   The IDEA key-wrap algorithm encrypts an IDEA content-encryption key
   with an IDEA key-encryption key.  The IDEA key-wrap algorithm is
   defined by:

   1.  Let the content-encryption key (16 octets) be called CEK
   2.  Compute an 8 octet key checksum value on CEK as described in
       [CMS], section 12.6.1, call the result ICV.
   3.  Let CEKICV := CEK || ICV.
   4.  Generate 8 octets at random, call the result IV.
   5.  Encrypt CEKICV using IDEA in CBC mode and the key-encryption key.
       Use the random value generated in the previous step as the
       initialization vector (IV).  Call the ciphertext TEMP1.
   6.  Let TEMP2 = IV || TEMP1.
   7.  Reverse the order of the octets in TEMP2.  That is, the most
       significant (first) octet is swapped with the least significant
       (last) octet, and so on.  Call the result TEMP3.
   8.  Encrypt TEMP3 using IDEA in CBC mode and the key-encryption key.
       Use an initialization vector (IV) of 0x4adda22c79e82105.  The
       ciphertext is 32 octets long.

3.2 IDEA Key Unwrap

   The IDEA key-unwrap algorithm decrypts an IDEA content-encryption key
   using an IDEA key-encryption key.  The IDEA key-unwrap algorithm is
   defined by:





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RFC 3058            IDEA Encryption Algorithm in CMS       February 2001


   1.  If the wrapped content-encryption key is not 32 octets, then
       error.
   2.  Decrypt the wrapped content-encryption key using IDEA in CBC mode
       with the key-encryption key.  Use an initialization vector (IV)
       of 0x4adda22c79e82105.  Call the output TEMP3.
   3.  Reverse the order of the octets in TEMP3.  That is, the most
       significant (first) octet is swapped with the least significant
       (last) octet, and so on.  Call the result TEMP2.
   4.  Decompose the TEMP2 into IV and TEMP1.  IV is the most
       significant (first) 8 octets, and TEMP1 is the remaining (last)
       24 octets.
   5.  Decrypt TEMP1 using IDEA in CBC mode with the key-encryption key.
       Use the IV value from the previous step as the initialization
       vector.  Call the plaintext CEKICV.
   6.  Decompose the CEKICV into CEK and ICV.  CEK is the most
       significant (first) 16 octets, and ICV is the least significant
       (last) 8 octets.
   7.  Compute an 8 octet key checksum value on CEK as described in
       [CMS], section 12.6.1.  If the computed key checksum value does
       not match the decrypted key checksum value, ICV, then error.
   8.  Use CEK as the content-encryption key.

4. SMIMECapabilities Attribute

   An S/MIME client can announce the set of cryptographic functions it
   supports by using the S/MIME capabilities attribute as specified in
   [SMIME3].  This attribute provides a partial list of OIDs of
   cryptographic functions and must be signed by the client.  These OIDs
   should be logically separated in functional categories and MUST be
   ordered with respect to their preference.  If an S/MIME client is
   required to support symmetric encryption and key wrapping based on
   IDEA, the capabilities attribute MUST contain the above specified
   OIDs in the category of symmetric algorithms and key encipherment
   algorithms.  IDEA does not require additional OID parameters since it
   has a fixed key length of 128 bits.

   The SMIMECapability SEQUENCE representing the IDEA symmetric
   encryption algorithm MUST include the IDEA-CBC OID in the
   capabilityID field and the parameters field MUST be absent.  The
   SMIMECapability SEQUENCE for IDEA encryption SHOULD be included in
   the symmetric encryption algorithms portion of the SMIMECapabilities
   list.  The SMIMECapability SEQUENCE representing IDEA MUST be DER-
   encoded as follows: 300D 060B 2B06 0104 0181 3C07 0101 02.

   The SMIMECapability SEQUENCE representing the IDEA key wrapping
   algorithm MUST include the id-alg-CMSIDEAwrap OID in the capabilityID
   field and the parameters field of KeyWrapAlgorithm MUST be absent.
   The SMIMECapability SEQUENCE for IDEA key wrapping SHOULD be included



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