Internet Draft                                         S. Teiwes,
draft-ietf-smime-idea-00.txt
draft-ietf-smime-idea-01.txt                           P. Hartmann,
March 29,
August 26, 1999                                        D. Kuenzi,
Expires in six months			               Ascom Systec			                   iT_Security Ltd.

   Incorporation of the IDEA encryption algorithm Encryption Algorithm in S/MIME

Status of this memo Memo

   This document is an Internet-Draft. Internet-Draft and is in full conformance with
   all provisions of section 10 of RFC2026. Internet-Drafts are
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1. Introduction

   This memo describes how to incorporate the IDEA (International Data
   Encryption Algorithm) [IDEA] encryption algorithm into

   S/MIME (Secure/Multipurpose Internet Mail Extensions) [SMIME2, SMIME3]. The
   S/MIME standard provides
   SMIME3] is a consistent way to send and receive specification for secure sending and receiving of MIME
   [MIME] data. Information security services are implemented Based on the basis of a set of Internet MIME standard, S/MIME provides
   cryptographic functions. Thus, digital
   signatures are used services for secure authentication, message integrity and
   non-repudiation of
   origin, origin by using digital signatures. It also
   supports privacy and data integrity, whereas data encryption is used to assure
   data security and privacy. by using encryption. The S/MIME is constructed as an open system. Its functionality for
   information security purposes
   framework can be flexibly extended to meet new future requirements. At
   However, its extentability can also be used to introduce specific
   add-on functionality which might be desired in messaging applications.

   This memo specifies how to incorporate IDEA (International Data
   Encryption Algorithm) into S/MIME as an additional algorithm for
   symmetric encryption. Today, IDEA is widely applied in e-business
   applications. However, it is not part of the S/MIME specification given
   in [SMIME3]. Often, encryption algorithms are part of a security policy,
   and organizations usually have their own preferences in this respect.
   Therefore, it is beneficial to have the same time choice between different
   well-known encryption algorithms. Especially for those organization
   who make already use of IDEA on a wide scale it is assured of high interest
   that extended systems
   will be compatible with non-extended systems. IDEA is also available S/MIME. It is the intention of this memo
   to provide the OIDs and algorithms required to include IDEA 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 maintained by 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.

   According to S/MIME v3 [SMIME3] sending and receiving agents MUST
   provide

   This draft is being discussed on the DES EDE3 CBC [3DES] [DES] for content encryption and
   decryption. Receiving agents SHOULD also support RC2 [RC2] at "ietf-smime" mailing list. To
   subscribe, send a key
   size of 40 bits. However, there are no general restrictions on message to:
        ietf-smime-request@imc.org
   with the
   application of encryption algorithms in S/MIME as long as they are
   specified by a valid object identifier. The ability of strong
   encryption is of general interest, but it is of particular interest
   for instance in electronic commerce applications. Thus, the extension
   of the S/MIME capabilities by the strong and efficient IDEA
   encryption algorithm is benificial.

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

   This draft is being discussed on the "ietf-smime" mailing list. To
   subscribe, send a message to:
        ietf-smime-request@imc.org
   with the single word
        subscribe single word
        subscribe
   in the body of the message. There is a Web site for the mailing list
   at <http://www.imc.org/ietf-smime/>

2. Comments On The IDEA Encryption Algorithm

   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 an encryption algorithm which would replace the DES
   algorithm. IDEA uses a 128-bit secret key and encrypts one 64-bit
   block at a time. The algorithm is generally considered to be very
   secure. It was particularly strengthened to protect against
   differential cryptoanalysis attacks.

   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".

   More information on IDEA and source code can be found at
   <http://www.ascom.ch/infosec/idea.html>.

3. IDEA Object Identifier For S/MIME for Content and Key Encryption

   The PKCS #7 message format [PKCS7] 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. A concrete Each algorithm which is used for
   encryption purposes MUST must be specified by a unique algorithm identifier. In
   For example, in the special case of content encryption, the
   ContentEncryptionAlgorithmIdentifier specifies the applied algorithm.

   S/MIME v3 requires only algorithm to be
   applied. However, according to [CMS] any symmetric encryption algorithm
   that agents MUST provide DES EDE3 CBC for
   content encryption, whereas RC2/40-bit is specified a CMS implementation includes as optional.
   IDEA can a content-encryption algorithm
   must also be simply included as a key-encryption algorithm.

   IDEA is added to the set of optional content symmetric encryption algorithms
   in S/MIME by providing its two unique S/MIME object identifier. This
   corresponds to identifiers (OIDs). One OID
   defines content encryption and the ContentEncryptionAlgorithmIdentifier of PKCS #7.
   An other one key encryption. Thus an
   S/MIME agent can apply the IDEA algorithm either for content or key encryption
   simply by
   selecting its the corresponding object identifier, supplying the required
   parameter, and starting the corresponding program code.

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

   The object identifier for IDEA content-encryption algorithm in CBC mode is given by has the object
   identifier

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

   The algorithm's identifier's parameters field contains the initial
   vector iv is IV as an optional parameter parameter.

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

   If iv IV is specified as above, it MUST must be used as initial vector. In
   this case, the ciphertext MUST NOT must not include the initial vector. If
   iv
   IV is not specified, the first 64 bits of the ciphertext MUST must be
   taken
   considered as the initial vector.

   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 memo.

   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:

   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. Consequence On on S/MIME Capabilities Attribute

   An S/MIME client SHOULD should announce the set of cryptographic functions
   it supports by using the S/MIME capabilities attribute. This
   attribute provides a partial list of OIDs of cryptographic functions
   and MUST must be signed by the client. The function's functions' OIDs SHOULD should be
   logically separated in functional categories and MUST must be ordered with
   respect to their preference. If an S/MIME client is required to
   support strong symmetric encryption by IDEA-CBC, with IDEA, the capabilities attribute
   MUST
   must contain the above specified OID OIDs in the category of symmetric
   algorithms. IDEA-CBC IDEA does not require additional OID parameters as it
   uses a fixed key length of 128 bits is propagated. bits.

5. Activation of IDEA In in S/MIME

   When a sending agent creates an encrypted message, it has to decide
   which type of encryption algorithm to use. In general, general the decision
   process involves using information obtained from the capabilities lists
   included in messages received from the recipient, as well as
   out-of-band other
   information such as private agreements, user preferences, legal
   restrictions, etc.

   For example, in the broad field of electronic commerce weak If users require IDEA for symmetric encryption, as represented by RC2/40, is regarded to be unacceptable.
   Strong encryption can
   it must be enforced on supported by the basis of a security policy.
   This policy SHOULD include an agreement on at least one desired
   strong encryption algorithms to be used in S/MIME. In this case it
   is required that S/MIME clients on both at the sending and the
   receiving end MUST support the desired encryption algorithms. Thus,
   if IDEA-CBC is chosen to be used as encryption algorithm, it MUST
   be supported by the S/MIME clients side, and it MUST 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.

   [SMIME2] "S/MIME Version 2 Message Specification", RFC 2311, and
   "S/MIME Version 2 Certificate Handling", RFC 2312.

   [SMIME3] "S/MIME Version 3 Message Specification", Internet Draft
   draft-ietf-smime-msg-xx, Certificate Handling", RFC 2632, and
   "S/MIME Version 3 Certificate
   Handling", Internet Draft draft-ietf-smime-cert-xx.

   [MIME-SPEC] Message Specification", RFC 2633.

   [MIME] The primary definition of MIME.
   "MIME Part 1: Format of Internet Message Bodies", RFC 2045; 2045.
   "MIME Part 2: Media Types", RFC 2046; 2046.
   "MIME Part 3: Message Header Extensions for Non-ASCII Text", RFC 2047; 2047.
   "MIME Part 4: Registration Procedures", RFC 2048; 2048.
   "MIME Part 5: Conformance Criteria and Examples", RFC 2049

   [3DES] W. Tuchman, "Hellman Presents No Shortcut Solutions To DES,"
   IEEE Spectrum, vol. 16, no. 7, July 1979, pp. 40-41.

   [DES] ANSI X3.106, "American National Standard for Information
   Systems- Data Link Encryption," American National Standards
   Institute, 1983.

   [RC2] "A Description of the RC2 (r) Encryption Algorithm", RFC 2268

   [MUSTSHOULD] "Key words for use in RFCs to Indicate Requirement
   Levels", 2049.

   [CMS] "Cryptographic Message Syntax", RFC 2119 2630.

   [PKCS7] "PKCS #7: Cryptographic Message Syntax Version 1.5", RFC 2315 2315.

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 an encryption algorithm which would replace the DES
   algorithm.

   IDEA uses 128-bit secret keys and encrypts one 64-bit block at a
   time. Experts in cryptography consider IDEA to be a highly secure
   symmetric cipher [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".

   More information on IDEA and source code can be found at
   <http://www.ascom.com/infosec/idea.html>.

C. Intellectual Property Notice

   IDEA (TM) is protected by international copyright law and in addition
   it has been patented in the United States States, Japan, and in most of the
   European countries. The patent is held by Ascom Ltd.

   Non-commercial use of IDEA is free.
   Commercial licenses can be easily obtained via online order or by
   contacting idea@ascom.ch.

C. Detailed licensing information can be found
   at <http://www.ascom.com/infosec/idea.html>.

D. Authors' Address

   Ascom Systec

   iT_Security Ltd.
   Gewerbepark
   P.O.Box
   5506 Maegenwil,
   Badenerstrasse 530

   CH-8048 Zurich, Switzerland

   Phone: +41 62 889 5964 1 236 9900
   Fax  : +41 1 236 9990
   Email: {stephan.teiwes,peter.hartmann,diego.kuenzi}@ascom.ch {stephan.teiwes,peter.hartmann,diego.kuenzi}@itsec.ch