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rfc:rfc3058

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.

Teiwes, et al. Informational [Page 1] 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.

Teiwes, et al. Informational [Page 2] 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:

Teiwes, et al. Informational [Page 3] 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

Teiwes, et al. Informational [Page 4] RFC 3058 IDEA Encryption Algorithm in CMS February 2001

 in the key encipherment algorithms portion of the SMIMECapabilities
 list.  The SMIMECapability SEQUENCE representing IDEA key wrapping
 MUST be DER-encoded as follows: 300D 060B 2B06 0104 0181 3C07 0101
 06.
 The ASN.1 notation of the SMIMECapability SEQUENCE representing IDEA
 is
    SMIMECapability ::= SEQUENCE {
       capabilityID OBJECT IDENTIFIER,
       parameters ANY DEFINED BY capabilityID OPTIONAL }
 where capabilityID is IDEA-CBC (no parameters) for IDEA content
 encryption in CBC mode or capabilityID is id-alg-CMSIDEAwrap (no
 parameters) for IDEA key wrapping.

5. Activation of IDEA in S/MIME Clients

 When a sending agent creates an encrypted message, it has to decide
 which type of encryption algorithm to use.  In general the decision
 process involves information obtained from the capabilities lists
 included in messages received from the recipient, as well as other
 information such as private agreements, user preferences, legal
 restrictions, etc.  If users require IDEA for symmetric encryption,
 it must be supported by the S/MIME clients on both the sending and
 receiving side, and it must be set in the user preferences.

A. References

 [IDEA]       X. Lai, "On the design and security of block ciphers",
              ETH Series in Information Processing, J.L. Massey
              (editor), vol. 1, Hartung-Gorre Verlag Konstanz,
              Technische Hochschule (Zurich), 1992.  A. J. Menezes,
              P.C. v. Oorschot, S.A. Vanstone, "Handbook of Applied
              Cryptography," CRC Press New York, 1997, p. 265.  B.
              Schneier, "Applied Cryptography," 2nd ed., John Wiley &
              Sons Inc.  New York, 1996, pp. 319-325. IPR: see the
              "IETF Page of Intellectual Property Rights Notices",
              http://www.ietf.org/ipr.html
 [SMIME2]     Dusse, S., Hoffman, P., Ramsdell, B., Lundblade, l. and
              L. Repka, "S/MIME Version 2 Message Specification", RFC
              2311, March 1998.
 [SMIME2]     Dusse, S., Hoffman, P., Ramsdell, B. and J. Weinstein,
              "S/MIME Version 2 Certificate Handling", RFC 2312, March
              1998.

Teiwes, et al. Informational [Page 5] RFC 3058 IDEA Encryption Algorithm in CMS February 2001

 [SMIME3]     Dusse, S., Hoffman, P., Ramsdell, B. and J. Weinstein,
              "S/MIME Version 3 Certificate Handling", RFC 2632, March
              1998.
 [SMIME3]     Ramsdell, B., "S/MIME Version 3 Message Specification",
              RFC 2633, June 1999.
 [MUSTSHOULD] Bradner, S.,"Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.
 [CMS]        Housley, R., "Cryptographic Message Syntax", RFC 2630,
              June 1999.
 [PKCS7]      Kaliski, B., "PKCS #7: Cryptographic Message Syntax
              Version 1.5", RFC 2315, March 1998.

B. Comments on IDEA Security and Standards

 The IDEA algorithm was developed in a joint project involving the
 Swiss Federal Institute of Technology in Zurich (Dr. X. Lai and Prof.
 J.L. Massey) and Ascom Ltd.  The aim of the project was to develop a
 strong encryption algorithm that could replace the DES algorithm.
 IDEA uses 128-bit secret keys and encrypts one 64-bit block at a time
 [IDEA].  It was particularly strengthened to protect against
 differential cryptoanalysis attacks.  For the full 8-round IDEA there
 is no attack known which is better than exhaustive search on the
 total 128-bit key space.
 IDEA permits the implementation of standard Electronic Data
 Interchange applications.  It has been entered in the ISO/IEC
 register for encryption algorithms and incorporated in the "SECURITY
 GUIDE LINES" code list by the UNI/EDIFACT "SECURITY JOINT WORKING
 GROUP".

C. Intellectual Property Rights Notice

 Ascom Ltd. holds the patent to IDEA.  In accordance with the
 intellectual property rights procedures of the IETF standards
 process, Ascom offers a non-exclusive license under reasonable and
 non-discriminatory terms and conditions.
 IDEA(TM) is protected by international copyright law and in addition
 has been patented in several countries.  Because Ascom wants to make
 this highly secure algorithm widely available, the non-commercial use
 of this algorithm is free.

Teiwes, et al. Informational [Page 6] RFC 3058 IDEA Encryption Algorithm in CMS February 2001

 Any party wishing to know more about IDEA or to request a license
 should visit the web sites <http://www.media-crypt.com/>,
 <http://www.it-sec.com/> or send an e-mail to info@media-crypt.com or
 Idea@it-sec.com.

D. Acknowledgements

 We would like to thank Russ Housley, Jim Schaad and Francois Zeller
 for their contributions to this document.

E. Authors' Addresses

 Stephan Teiwes
 iT_Security AG (Ltd.)
 Badenerstrasse 530
 CH-8048 Zurich, Switzerland
 Phone: +41 1 404 8200
 Fax  : +41 1 404 8201
 EMail: stephan.teiwes@it-sec.com
 Peter Hartmann
 iT_Security AG (Ltd.)
 Badenerstrasse 530
 CH-8048 Zurich, Switzerland
 Phone: +41 1 404 8200
 Fax  : +41 1 404 8201
 EMail: peter.hartmann@it-sec.com
 Diego Kuenzi
 724 Solutions Inc.
 Bahnhofstrasse 16
 CH-5600 Lenzburg, Switzerland
 Phone: +41 62 888 3070
 Fax:   +41 62 888 3071
 EMail: dkuenzi@724.com

Teiwes, et al. Informational [Page 7] RFC 3058 IDEA Encryption Algorithm in CMS February 2001

F. Full Copyright Statement

 Copyright (C) The Internet Society (2001).  All Rights Reserved.
 This document and translations of it may be copied and furnished to
 others, and derivative works that comment on or otherwise explain it
 or assist in its implementation may be prepared, copied, published
 and distributed, in whole or in part, without restriction of any
 kind, provided that the above copyright notice and this paragraph are
 included on all such copies and derivative works.  However, this
 document itself may not be modified in any way, such as by removing
 the copyright notice or references to the Internet Society or other
 Internet organizations, except as needed for the purpose of
 developing Internet standards in which case the procedures for
 copyrights defined in the Internet Standards process must be
 followed, or as required to translate it into languages other than
 English.
 The limited permissions granted above are perpetual and will not be
 revoked by the Internet Society or its successors or assigns.
 This document and the information contained herein is provided on an
 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Teiwes, et al. Informational [Page 8]

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