draft-ietf-smime-idea-01.txt   draft-ietf-smime-idea-02.txt 
Internet Draft S. Teiwes, Internet Draft S. Teiwes,
draft-ietf-smime-idea-01.txt P. Hartmann, draft-ietf-smime-idea-02.txt P. Hartmann,
August 26, 1999 D. Kuenzi, February 22, 1999 D. Kuenzi,
Expires in six months iT_Security Ltd. Expires in six months iT_Security Ltd.
Incorporation of the IDEA Encryption Algorithm in S/MIME Incorporation of the IDEA Encryption Algorithm in S/MIME
Status of this Memo Status of this Memo
This document is an Internet-Draft and is in full conformance with This document is an Internet-Draft and is in full conformance with
all provisions of section 10 of RFC2026. Internet-Drafts are all provisions of section 10 of RFC2026. Internet-Drafts are
working documents of the Internet Engineering Task Force (IETF), working documents of the Internet Engineering Task Force (IETF),
its areas, and its working groups. Note that other groups may also its areas, and its working groups. Note that other groups may also
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Rim), ftp.ietf.org (US East Coast), or ftp.isi.edu (US West Coast). Rim), ftp.ietf.org (US East Coast), or ftp.isi.edu (US West Coast).
1. Introduction 1. Introduction
S/MIME (Secure/Multipurpose Internet Mail Extensions) [SMIME2,
SMIME3] is a specification for secure sending and receiving of MIME
[MIME] data. Based on the Internet MIME standard, S/MIME provides
cryptographic services for authentication, message integrity and
non-repudiation of origin by using digital signatures. It also
supports privacy and data security by using encryption. The S/MIME
framework can be flexibly extended to meet future requirements.
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 This memo specifies how to incorporate IDEA (International Data
Encryption Algorithm) into S/MIME as an additional algorithm for Encryption Algorithm) [IDEA] into S/MIME [SMIME2, SMIME3] as an
symmetric encryption. Today, IDEA is widely applied in e-business additional algorithm for symmetric encryption. Today, IDEA is widely
applications. However, it is not part of the S/MIME specification given applied in electronic business applications. But it is not
in [SMIME3]. Often, encryption algorithms are part of a security policy, considered in the specification [SMIME3]. Encryption algorithms are
and organizations usually have their own preferences in this respect. part of an organizations' security policy. Typically, organizations
Therefore, it is beneficial to have the choice between different like to have their own preferences in this respect. Therefore, it is
well-known encryption algorithms. Especially for those organization beneficial to have the choice between different well-known encryption
who make already use of IDEA on a wide scale it is of high interest algorithms. Especially for those organization who make already use
that IDEA is also available S/MIME. It is the intention of this memo of IDEA on a wide scale it is of high interest that IDEA is also
to provide the OIDs and algorithms required to include IDEA in S/MIME available in S/MIME. It is the intention of this memo to provide the
for symmetric content and key encryption. 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 The general functional capabilities and preferences of S/MIME are
specified by the registered list of S/MIME object identifiers (OIDs). specified by the registered list of S/MIME object identifiers (OIDs).
This list of OIDs is maintained by the Internet Mail Consortium at This list of OIDs is maintained by the Internet Mail Consortium at
<http://www.imc.org/ietf-smime/oids.html>. <http://www.imc.org/ietf-smime/oids.html>.
The set of S/MIME functions provided by a client is expressed by the 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 S/MIME capabilities attribute. This attribute contains a list of OIDs
of supported cryptographic functions. of supported cryptographic functions.
This draft is being discussed on the "ietf-smime" mailing list. To This draft is being discussed on the "ietf-smime" mailing list. To
subscribe, send a message to: subscribe, send a message to:
ietf-smime-request@imc.org ietf-smime-request@imc.org
with the single word with the single word
subscribe subscribe
in the body of the message. There is a Web site for the mailing list in the body of the message. There is a Web site for the mailing list
at <http://www.imc.org/ietf-smime/> at <http://www.imc.org/ietf-smime/>
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 2. Object Identifier for Content and Key Encryption
The Cryptographic Message Syntax [CMS], derived from PKCS#7 [PKCS7], The Cryptographic Message Syntax [CMS], derived from PKCS#7 [PKCS7],
is the framework for the implementation of cryptographic functions in is the framework for the implementation of cryptographic functions in
S/MIME. It specifies data formats and encryption processes without S/MIME. It specifies data formats and encryption processes without
naming the cryptographic algorithms. Each algorithm which is used for naming the cryptographic algorithms. Each algorithm which is used
encryption purposes must be specified by a unique algorithm identifier. for encryption purposes must be specified by a unique algorithm
For example, in the special case of content encryption, the identifier. For example, in the special case of content encryption
ContentEncryptionAlgorithmIdentifier specifies the algorithm to be the ContentEncryptionAlgorithmIdentifier specifies the algorithm to
applied. However, according to [CMS] any symmetric encryption algorithm be applied. However, according to [CMS] any symmetric encryption
that a CMS implementation includes as a content-encryption algorithm algorithm that a CMS implementation includes as a content-encryption
must also be included as a key-encryption algorithm. algorithm must also be included as a key-encryption algorithm.
IDEA is added to the set of optional symmetric encryption algorithms IDEA is added to the set of optional symmetric encryption algorithms
in S/MIME by providing two unique object identifiers (OIDs). One OID in S/MIME by providing two unique object identifiers (OIDs). One OID
defines content encryption and the other one key encryption. Thus an defines content encryption and the other one key encryption. Thus an
S/MIME agent can apply IDEA either for content or key encryption by S/MIME agent can apply IDEA either for content or key encryption by
selecting the corresponding object identifier, supplying the required selecting the corresponding object identifier, supplying the required
parameter, and starting the program code. parameter, and starting the program code.
For content encryption the use of IDEA in cipher block chaining (CBC) For content encryption the use of IDEA in cipher block chaining (CBC)
mode is recommended. The key length is fixed to 128 bits. mode is recommended. The key length is fixed to 128 bits.
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::= { iso(1) identified-organization(3) ::= { iso(1) identified-organization(3)
usdod(6) oid(1) private(4) enterprises(1) usdod(6) oid(1) private(4) enterprises(1)
ascom(188) systec(7) security(1) algorithms(1) 2 } ascom(188) systec(7) security(1) algorithms(1) 2 }
The identifier's parameters field contains the initial The identifier's parameters field contains the initial
vector IV as an optional parameter. vector IV as an optional parameter.
IDEA-CBCPar ::= SEQUENCE { IDEA-CBCPar ::= SEQUENCE {
IV OCTET STRING OPTIONAL -- exactly 8 octets } IV OCTET STRING OPTIONAL -- exactly 8 octets }
If IV is specified as above, it must be used as initial vector. In 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 this case, the ciphertext MUST NOT include the initial vector. If
IV is not specified, the first 64 bits of the ciphertext must be IV is not specified, the first 64 bits of the ciphertext MUST be
considered as the initial vector. considered as the initial vector. However, this alternative of not
including the IV SHOULD NOT be applied in S/MIME.
The key-wrap/unwrap algorithms used to encrypt/decrypt an IDEA The key-wrap/unwrap algorithms used to encrypt/decrypt an IDEA
content-encryption key with an IDEA key-encryption key are content-encryption key with an IDEA key-encryption key are
specified in the following section. Generation and distribution specified in the following section. Generation and distribution
of IDEA key-encryption keys are beyond the scope of this memo. of IDEA key-encryption keys are beyond the scope of this document.
The IDEA key-encryption algorithm has the object identifier The IDEA key-encryption algorithm has the object identifier
id-alg-CMSIDEAwrap OBJECT IDENTIFIER id-alg-CMSIDEAwrap OBJECT IDENTIFIER
::= { iso(1) identified-organization(3) ::= { iso(1) identified-organization(3)
usdod(6) oid(1) private(4) enterprises(1) usdod(6) oid(1) private(4) enterprises(1)
ascom(188) systec(7) security(1) algorithms(1) 6 } ascom(188) systec(7) security(1) algorithms(1) 6 }
The identifier's parameters field must be NULL. The identifier's parameters field MUST be NULL.
3. Key-Wrapping and Unwrapping 3. Key-Wrapping and Unwrapping
In the following subsections IDEA key-wrap and key-unwrap algorithms In the following subsections IDEA key-wrap and key-unwrap algorithms
are specified in conformance with [CMS], section 12.3. are specified in conformance with [CMS], section 12.3.
3.1 IDEA Key Wrap 3.1 IDEA Key Wrap
The IDEA key-wrap algorithm encrypts an IDEA content-encryption key The IDEA key-wrap algorithm encrypts an IDEA content-encryption key
with an IDEA key-encryption key. The IDEA key-wrap algorithm is defined with an IDEA key-encryption key. The IDEA key-wrap algorithm is
by: defined by:
1. Let the content-encryption key (16 octets) be called CEK 1. Let the content-encryption key (16 octets) be called CEK
2. Compute an 8 octet key checksum value on CEK as described 2. Compute an 8 octet key checksum value on CEK as described
in [CMS], section 12.6.1, call the result ICV. in [CMS], section 12.6.1, call the result ICV.
3. Let CEKICV := CEK || ICV. 3. Let CEKICV := CEK || ICV.
4. Generate 8 octets at random, call the result IV. 4. Generate 8 octets at random, call the result IV.
5. Encrypt CEKICV using IDEA in CBC mode and the key-encryption key. 5. Encrypt CEKICV using IDEA in CBC mode and the key-encryption key.
Use the random value generated in the previous step as the Use the random value generated in the previous step as the
initialization vector (IV). Call the ciphertext TEMP1. initialization vector (IV). Call the ciphertext TEMP1.
6. Let TEMP2 = IV || TEMP1. 6. Let TEMP2 = IV || TEMP1.
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with the key-encryption key. Use an initialization vector (IV) with the key-encryption key. Use an initialization vector (IV)
of 0x4adda22c79e82105. Call the output TEMP3. of 0x4adda22c79e82105. Call the output TEMP3.
3. Reverse the order of the octets in TEMP3. That is, the most 3. Reverse the order of the octets in TEMP3. That is, the most
significant (first) octet is swapped with the least significant significant (first) octet is swapped with the least significant
(last) octet, and so on. Call the result TEMP2. (last) octet, and so on. Call the result TEMP2.
4. Decompose the TEMP2 into IV and TEMP1. IV is the most significant 4. Decompose the TEMP2 into IV and TEMP1. IV is the most significant
(first) 8 octets, and TEMP1 is the remaining (last) 24 octets. (first) 8 octets, and TEMP1 is the remaining (last) 24 octets.
5. Decrypt TEMP1 using IDEA in CBC mode with the key-encryption key. 5. Decrypt TEMP1 using IDEA in CBC mode with the key-encryption key.
Use the IV value from the previous step as the initialization Use the IV value from the previous step as the initialization
vector. Call the plaintext CEKICV. vector. Call the plaintext CEKICV.
6. Decompose the CEKICV into CEK and ICV. CEK is the most significant 6. Decompose the CEKICV into CEK and ICV. CEK is the most
(first) 16 octets, and ICV is the least significant (last) 8 octets. 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 7. Compute an 8 octet key checksum value on CEK as described
in [CMS], section 12.6.1. If the computed key checksum value in [CMS], section 12.6.1. If the computed key checksum value
does not match the decrypted key checksum value, ICV, then error. does not match the decrypted key checksum value, ICV, then error.
8. Use CEK as the content-encryption key. 8. Use CEK as the content-encryption key.
4. Consequence on S/MIME Capabilities Attribute 4. SMIMECapabilities Attribute
An S/MIME client should announce the set of cryptographic functions An S/MIME client can announce the set of cryptographic functions
it supports by using the S/MIME capabilities attribute. This it supports by using the S/MIME capabilities attribute as specified
attribute provides a partial list of OIDs of cryptographic functions in [SMIME3]. This attribute provides a partial list of OIDs of
and must be signed by the client. The functions' OIDs should be cryptographic functions and must be signed by the client. These OIDs
logically separated in functional categories and must be ordered with should be logically separated in functional categories and MUST be
respect to their preference. If an S/MIME client is required to ordered with respect to their preference. If an S/MIME client is
support symmetric encryption with IDEA, the capabilities attribute required to support symmetric encryption and key wrapping based on
must contain the above specified OIDs in the category of symmetric IDEA, the capabilities attribute MUST contain the above specified
algorithms. IDEA does not require additional OID parameters as it OIDs in the category of symmetric algorithms and key encipherment
uses a fixed key length of 128 bits. 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
encrytion 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: 300F 060B 2B06 0104 0181 3C07 0101 0205 00.
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
in the key encipherment algorithms portion of the SMIMECapabilities
list. The SMIMECapability SEQUENCE representing IDEA key wrapping
MUST be DER-encoded as follows: 300F 060B 2B06 0104 0181 3C07 0101
0605 00.
5. Activation of IDEA in S/MIME 5. Activation of IDEA in S/MIME
When a sending agent creates an encrypted message, it has to decide When a sending agent creates an encrypted message, it has to decide
which type of encryption algorithm to use. In general the decision which type of encryption algorithm to use. In general the decision
process involves information obtained from the capabilities lists process involves information obtained from the capabilities lists
included in messages received from the recipient, as well as other included in messages received from the recipient, as well as other
information such as private agreements, user preferences, legal information such as private agreements, user preferences, legal
restrictions, etc. If users require IDEA for symmetric encryption, restrictions, etc. If users require IDEA for symmetric encryption,
it must be supported by the S/MIME clients on both the sending and it must be supported by the S/MIME clients on both the sending and
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Cryptography," CRC Press New York, 1997, p. 265. Cryptography," CRC Press New York, 1997, p. 265.
B. Schneier, "Applied Cryptography," 2nd ed., John Wiley & Sons Inc. B. Schneier, "Applied Cryptography," 2nd ed., John Wiley & Sons Inc.
New York, 1996, pp. 319-325. New York, 1996, pp. 319-325.
[SMIME2] "S/MIME Version 2 Message Specification", RFC 2311, and [SMIME2] "S/MIME Version 2 Message Specification", RFC 2311, and
"S/MIME Version 2 Certificate Handling", RFC 2312. "S/MIME Version 2 Certificate Handling", RFC 2312.
[SMIME3] "S/MIME Version 3 Certificate Handling", RFC 2632, and [SMIME3] "S/MIME Version 3 Certificate Handling", RFC 2632, and
"S/MIME Version 3 Message Specification", RFC 2633. "S/MIME Version 3 Message Specification", RFC 2633.
[MIME] The primary definition of MIME. [MUSTSHOULD] "Key words for use in RFCs to Indicate Requirement
"MIME Part 1: Format of Internet Message Bodies", RFC 2045. Levels", RFC 2119.
"MIME Part 2: Media Types", RFC 2046.
"MIME Part 3: Message Header Extensions for Non-ASCII Text", RFC 2047.
"MIME Part 4: Registration Procedures", RFC 2048.
"MIME Part 5: Conformance Criteria and Examples", RFC 2049.
[CMS] "Cryptographic Message Syntax", RFC 2630. [CMS] "Cryptographic Message Syntax", RFC 2630.
[PKCS7] "PKCS #7: Cryptographic Message Syntax Version 1.5", RFC 2315. [PKCS7] "PKCS #7: Cryptographic Message Syntax Version 1.5",
RFC 2315.
B. Comments on IDEA Security and Standards B. Comments on IDEA Security and Standards
The IDEA algorithm was developed in a joint project involving the The IDEA algorithm was developed in a joint project involving the
Swiss Federal Institute of Technology in Zurich (Dr. X. Lai and 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 Prof. J.L. Massey) and Ascom Ltd. The aim of the project was to
develop an encryption algorithm which would replace the DES develop an encryption algorithm which would replace the DES
algorithm. algorithm.
IDEA uses 128-bit secret keys and encrypts one 64-bit block at a IDEA uses 128-bit secret keys and encrypts one 64-bit block at a
skipping to change at line 254 skipping to change at line 266
symmetric cipher [IDEA]. It was particularly strengthened to protect symmetric cipher [IDEA]. It was particularly strengthened to protect
against differential cryptoanalysis attacks. For the full 8-round against differential cryptoanalysis attacks. For the full 8-round
IDEA there is no attack known which is better than exhaustive search IDEA there is no attack known which is better than exhaustive search
on the total 128-bit key space. on the total 128-bit key space.
IDEA permits the implementation of standard Electronic Data IDEA permits the implementation of standard Electronic Data
Interchange applications. It has been entered in the ISO/IEC register Interchange applications. It has been entered in the ISO/IEC register
for encryption algorithms and incorporated in the "SECURITY GUIDE for encryption algorithms and incorporated in the "SECURITY GUIDE
LINES" code list by the UNI/EDIFACT "SECURITY JOINT WORKING GROUP". LINES" code list by the UNI/EDIFACT "SECURITY JOINT WORKING GROUP".
More information on IDEA and source code can be found at More information on IDEA can be found at
<http://www.ascom.com/infosec/idea.html>. <http://www.it-sec.com/idea_alg.html>.
C. Intellectual Property Notice C. Intellectual Property Notice
IDEA (TM) is protected by international copyright law and in addition IDEA (TM) is protected by international copyright law and in addition
it has been patented in the United States, Japan, and in most of the it has been patented in the United States, Japan, and in most of the
European countries. The patent is held by Ascom Ltd. European countries. The patent is held by Ascom Ltd.
Non-commercial use of IDEA is free. Non-commercial use of IDEA is free.
Commercial licenses can be easily obtained via online order or by Commercial licenses can be easily obtained via online order or by
contacting idea@ascom.ch. Detailed licensing information can be found contacting idea@it-sec.com. Detailed licensing information can be found
at <http://www.ascom.com/infosec/idea.html>. at <http://www.it-sec.com/idea_lic.html>.
D. Authors' Address D. Acknowledgements
We would like to thank Jim Schaad and Francois Zeller for their
contributions to this document.
E. Authors' Address
iT_Security Ltd. iT_Security Ltd.
Badenerstrasse 530 Badenerstrasse 530
CH-8048 Zurich, Switzerland CH-8048 Zurich, Switzerland
Phone: +41 1 236 9900 Phone: +41 1 236 9900
Fax : +41 1 236 9990 Fax : +41 1 236 9990
Email: {stephan.teiwes,peter.hartmann,diego.kuenzi}@itsec.ch Email: {stephan.teiwes,peter.hartmann,diego.kuenzi}@it-sec.com
F. Full Copyright Statement
Copyright (C) The Internet Society (date). All Rights Reserved.
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or assist in its implementation may be prepared, copied, published
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are included on all such copies and derivative works. However, this
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The limited permissions granted above are perpetual and will not be
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