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Versions: 00 01 02 03 04 05 RFC 3657

S/MIME Working Group                                           S. Moriai
Internet Draft                                           NTT Corporation
Expiration Date: September 2003                                  A. Kato
                                                NTT Software Corporation
                                                              March 2003


            Use of the Camellia Encryption Algorithm in CMS

                   <draft-ietf-smime-camellia-02.txt>

Status of this Memo

    This document is an Internet-Draft and is in full conformance with
    all provisions of Section 10 of RFC2026.

    Internet-Drafts are working documents of the Internet Engineering
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    "ietf-smime" mailing list, or directly to the author.

Abstract

    This document specifies how to incorporate the Camellia encryption
    algorithm into the S/MIME Cryptographic Message Syntax (CMS) as an
    additional algorithm for symmetric encryption.  The relevant object
    identifiers (OIDs) and processing steps are provided so that
    Camellia may be used in the CMS specification (RFC 3369, RFC 3370)
    for content and key encryption.

    The key words "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD
    NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document (in
    uppercase, as shown) are to be interpreted as described in
    [RFC2119].

1. Introduction

    This document specifies the conventions for using the Camellia
    encryption algorithm [CamelliaSpec][CamelliaID] for encryption with
    the Cryptographic Message Syntax (CMS) [CMS].


Moriai, Kato                                                    [Page 1]

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    CMS values are generated using ASN.1 (X.208-88), using the Basic
    Encoding Rules (BER) (X.209-88) and the Distinguished Encoding Rules
    (DER) (X.509-88).

1.1 Camellia

    Camellia was jointly developed by Nippon Telegraph and Telephone
    Corporation and Mitsubishi Electric Corporation in 2000. Camellia
    specifies the 128-bit block size and 128-, 192-, and 256-bit key
    sizes, the same interface as the Advanced Encryption Standard (AES).
    Camellia is characterized by its suitability for both software and
    hardware implementations as well as its high level of security.
    From a practical viewpoint, it is designed to enable flexibility in
    software and hardware implementations on 32-bit processors widely
    used over the Internet and many applications, 8-bit processors used
    in smart cards, cryptographic hardware, embedded systems, and so on
    [CamelliaTech].  Moreover, its key setup time is excellent, and its
    key agility is superior to that of AES.

    Camellia has been scrutinized by the wide cryptographic community
    during several projects for evaluating crypto algorithms.  In
    particular, Camellia was selected as a recommended cryptographic
    primitive by the EU NESSIE (New European Schemes for Signatures,
    Integrity and Encryption) project [NESSIE] and also included in the
    list of cryptographic techniques for Japanese e-Government systems
    which are selected by the Japan CRYPTREC (Cryptography Research and
    Evaluation Committees) [CRYPTREC].

2. Object Identifiers for Content and Key Encryption

    This section provides the OIDs and processing information necessary
    for Camellia to be used for content and key encryption in CMS.

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

2.1 OIDs for Content Encryption

    Camellia is added to the set of symmetric content encryption
    algorithms defined in [CMSALG].  The Camellia content-encryption
    algorithm, in Cipher Block Chaining (CBC) mode, for the three
    different key sizes are identified by the following object
    identifiers:

       id-camellia128-cbc OBJECT IDENTIFIER ::=
           { iso(1) member-body(2) 392 200011 61 security(1)
             algorithm(1) symmetric-encryption-algorithm(1)
             camellia128-cbc(2) }


Moriai, Kato                                                    [Page 2]

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       id-camellia192-cbc OBJECT IDENTIFIER ::=
           { iso(1) member-body(2) 392 200011 61 security(1)
             algorithm(1) symmetric-encryption-algorithm(1)
             camellia192-cbc(3) }

       id-camellia256-cbc OBJECT IDENTIFIER ::=
           { iso(1) member-body(2) 392 200011 61 security(1)
             algorithm(1) symmetric-encryption-algorithm(1)
             camellia256-cbc(4) }

    The AlgorithmIdentifier parameters field MUST be present, and the
    parameters field MUST contain the value of IV:

       CamelliaCBCParameter ::= CamelliaIV  --  Initialization Vector

       CamelliaIV ::= OCTET STRING (SIZE(16))

    The plain text is padded according to Section 6.3 of [CMS].


2.2 OIDs for Key Encryption

    The key-wrap/unwrap procedures used to encrypt/decrypt a Camellia
    content-encryption key (CEK) with a Camellia key-encryption key
    (KEK) are specified in Section 3.  Generation and distribution of
    key-encryption keys are beyond the scope of this document.

    The Camellia key-encryption algorithm has the following object
    identifier:

      id-camellia128-wrap OBJECT IDENTIFIER ::=
              { iso(1) member-body(2) 392 200011 61 security(1)
                algorithm(1) key-wrap-algorithm(3)
                camellia128-wrap(2) }

      id-camellia192-wrap OBJECT IDENTIFIER ::=
              { iso(1) member-body(2) 392 200011 61 security(1)
                 algorithm(1) key-wrap-algorithm(3)
                 camellia192-wrap(3) }

      id-camellia256-wrap OBJECT IDENTIFIER ::=
              { iso(1) member-body(2) 392 200011 61 security(1)
                algorithm(1) key-wrap-algorithm(3)
                camellia256-wrap(4) }

    In all cases the parameters field of AlgorithmIdentifier MUST be
    absent, because the key wrapping procedure itself defines how and
    when to use an IV. The OID gives the KEK key size, but does not
    make any statements as to the size of the wrapped Camellia CEK.
    Implementations MAY use different KEK and CEK sizes.  Implements
    MUST support the CEK and the KEK having the same length.  If
    different lengths are supported, the KEK MUST be of equal or greater
    length than the CEK.


Moriai, Kato                                                    [Page 3]

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3. Key Wrap Algorithm

    Camellia key wrapping and unwrapping is done in conformance with the
    AES key wrap algorithm [AES-WRAP][RFC3394], because Camellia and AES
    have the same block and key sizes, i.e. the block size of 128 bits
    and key sizes of 128, 192, and 256 bits.

3.1 Notation and Definitions

    The following notation is used in the description of the key
    wrapping algorithms:

      Camellia(K, W)
                    Encrypt W using the Camellia codebook with key K
      Camellia-1(K, W)
                    Decrypt W using the Camellia codebook with key K
      MSB(j, W)     Return the most significant j bits of W
      LSB(j, W)     Return the least significant j bits of W
      B1 ^ B2       The bitwise exclusive or (XOR) of B1 and B2
      B1 | B2       Concatenate B1 and B2
      K             The key-encryption key K
      n             The number of 64-bit key data blocks
      s             The number of steps in the wrapping process, s = 6n
      P[i]          The ith plaintext key data block
      C[i]          The ith ciphertext data block
      A             The 64-bit integrity check register
      R[i]          An array of 64-bit registers where
                       i = 0, 1, 2, ..., n
      A[t], R[i][t] The contents of registers A and R[i] after encryption
                       step t.
      IV            The 64-bit initial value used during the wrapping
                       process.

    In the key wrap algorithm, the concatenation function will be used
    to concatenate 64-bit quantities to form the 128-bit input to the
    Camellia codebook.  The extraction functions will be used to split
    the 128-bit output from the Camellia codebook into two 64-bit
    quantities.

3.2 Camellia Key Wrap

    Key wrapping with Camellia is identical to Section 2.2.1 of
    [RFC3394] with "AES" replaced by "Camellia".

    The inputs to the key wrapping process are the KEK and the plaintext
    to be wrapped.  The plaintext consists of n 64-bit blocks,
    containing the key data being wrapped.  The key wrapping process is
    described below.

   Inputs:      Plaintext, n 64-bit values {P1, P2, ..., Pn}, and
                Key, K (the KEK).
   Outputs:     Ciphertext, (n+1) 64-bit values {C0, C1, ..., Cn}.


Moriai, Kato                                                    [Page 4]

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   1) Initialize variables.

       Set A0 to an initial value (see Section 3.4)
       For i = 1 to n
            R[0][i] = P[i]

   2) Calculate intermediate values.

       For t = 1 to s, where s = 6n
           A[t] = MSB(64, Camellia(K, A[t-1] | R[t-1][1])) ^ t
           For i = 1 to n-1
               R[t][i] = R[t-1][i+1]
           R[t][n] = LSB(64, Camellia(K, A[t-1] | R[t-1][1]))

   3) Output the results.

       Set C[0] = A[t]
       For i = 1 to n
           C[i] = R[t][i]

    An alternative description of the key wrap algorithm involves
    indexing rather than shifting.  This approach allows one to
    calculate the wrapped key in place, avoiding the rotation in the
    previous description.  This produces identical results and is more
    easily implemented in software.

   Inputs:  Plaintext, n 64-bit values {P1, P2, ..., Pn}, and
            Key, K (the KEK).
   Outputs: Ciphertext, (n+1) 64-bit values {C0, C1, ..., Cn}.

   1) Initialize variables.

       Set A = IV, an initial value (see Section 3.4)
       For i = 1 to n
           R[i] = P[i]

   2) Calculate intermediate values.

       For j = 0 to 5
           For i=1 to n
               B = Camellia(K, A | R[i])
               A = MSB(64, B) ^ t where t = (n*j)+i
               R[i] = LSB(64, B)

   3) Output the results.

       Set C[0] = A
       For i = 1 to n
           C[i] = R[i]


3.3 Camellia Key Unwrap

    Key unwrapping with Camellia is identical to Section 2.2.2 of

Moriai, Kato                                                    [Page 5]

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    [RFC3394], with "AES" replaced by "Camellia".

    The inputs to the unwrap process are the KEK and (n+1) 64-bit blocks
    of ciphertext consisting of previously wrapped key.  It returns n
    blocks of plaintext consisting of the n 64-bit blocks of the
    decrypted key data.

   Inputs:  Ciphertext, (n+1) 64-bit values {C0, C1, ..., Cn}, and
            Key, K (the KEK).
   Outputs: Plaintext, n 64-bit values {P1, P2, ..., Pn}.

   1) Initialize variables.

       Set A[s] = C[0] where s = 6n
       For i = 1 to n
           R[s][i] = C[i]

   2) Calculate the intermediate values.

       For t = s to 1
           A[t-1] = MSB(64, Camellia-1(K, ((A[t] ^ t) | R[t][n]))
           R[t-1][1] = LSB(64, Camellia-1(K, ((A[t]^t) | R[t][n]))
           For i = 2 to n
               R[t-1][i] = R[t][i-1]

   3) Output the results.

       If A[0] is an appropriate initial value (see Section 3.4),
       Then
           For i = 1 to n
               P[i] = R[0][i]
       Else
           Return an error

    The unwrap algorithm can also be specified as an index based
    operation, allowing the calculations to be carried out in place.
    Again, this produces the same results as the register shifting
    approach.

   Inputs:  Ciphertext, (n+1) 64-bit values {C0, C1, ..., Cn}, and
            Key, K (the KEK).
   Outputs: Plaintext, n 64-bit values {P0, P1, K, Pn}.

   1) Initialize variables.

       Set A = C[0]
       For i = 1 to n
           R[i] = C[i]

   2) Compute intermediate values.

       For j = 5 to 0
           For i = n to 1
               B = Camellia-1(K, (A ^ t) | R[i]) where t = n*j+i

Moriai, Kato                                                    [Page 6]

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               A = MSB(64, B)
               R[i] = LSB(64, B)

   3) Output results.

   If A is an appropriate initial value (see Section 3.4),
   Then
       For i = 1 to n
           P[i] = R[i]
   Else
       Return an error


3.4 Key Data Integrity -- the Initial Value

    The initial value (IV) refers to the value assigned to A[0] in the
    first step of the wrapping process.  This value is used to obtain an
    integrity check on the key data.  In the final step of the
    unwrapping process, the recovered value of A[0] is compared to the
    expected value of A[0].  If there is a match, the key is accepted as
    valid, and the unwrapping algorithm returns it.  If there is not a
    match, then the key is rejected, and the unwrapping algorithm
    returns an error.

    The exact properties achieved by this integrity check depend on the
    definition of the initial value.  Different applications may call
    for somewhat different properties; for example, whether there is
    need to determine the integrity of key data throughout its lifecycle
    or just when it is unwrapped.  This specification defines a default
    initial value that supports integrity of the key data during the
    period it is wrapped (in Section 3.4.1).  Provision is also made to
    support alternative initial values (in Section 3.4.2).

3.4.1 Default Initial Value

    The default initial value (IV) is defined to be the hexadecimal
    constant:

       A[0] = IV = A6A6A6A6A6A6A6A6

    The use of a constant as the IV supports a strong integrity check on
    the key data during the period that it is wrapped.  If unwrapping
    produces A[0] = A6A6A6A6A6A6A6A6, then the chance that the key data
    is corrupt is 2^-64.  If unwrapping produces A[0] any other value,
    then the unwrap must return an error and not return any key data.

3.4.2 Alternative Initial Values

    When the key wrap is used as part of a larger key management
    protocol or system, the desired scope for data integrity may be more
    than just the key data or the desired duration for more than just
    the period that it is wrapped.  Also, if the key data is not just an
    Camellia key, it may not always be a multiple of 64 bits.
    Alternative definitions of the initial value can be used to address

Moriai, Kato                                                    [Page 7]

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    such problems.  According to [RFC3394], NIST will define alternative
    initial values in future key management publications as needed.  In
    order to accommodate a set of alternatives that may evolve over
    time, key wrap implementations that are not application-specific
    will require some flexibility in the way that the initial value is
    set and tested.

4. SMIMECapabilities Attribute

    An S/MIME client 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 be signed by the client.  The functions' OIDs SHOULD be
    logically separated in functional categories and MUST be ordered
    with respect to their preference.

    RFC 2633 [RFC2633], Section 2.5.2 defines the SMIMECapabilities
    signed attribute (defined as a SEQUENCE of SMIMECapability
    SEQUENCEs) to be used to specify a partial list of algorithms that
    the software announcing the SMIMECapabilities can support.

    If an S/MIME client is required to support symmetric encryption with
    Camellia, the capabilities attribute MUST contain the Camellia OID
    specified above in the category of symmetric algorithms.  The
    parameter associated with this OID MUST be CamelliaSMimeCapability.

       CamelliaSMimeCapabilty ::= NULL

    The SMIMECapability SEQUENCE representing Camellia MUST be
    DER-encoded as the following hexadecimal strings:

       Key Size                   Capability
        128          30 0f 06 0b 2a 83 08 8c 9a 4b 3d 01 01 01 02 05 00
        196          30 0f 06 0b 2a 83 08 8c 9a 4b 3d 01 01 01 03 05 00
        256          30 0f 06 0b 2a 83 08 8c 9a 4b 3d 01 01 01 04 05 00

    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, and so on. If users require Camellia 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.

5. Security Considerations

    This document specifies the use of Camellia for encrypting the
    content of a CMS message and for encrypting the symmetric key used
    to encrypt the content of a CMS message, and the other mechanisms
    are the same as the existing ones.  Therefore, the security
    considerations described in the CMS specifications [CMS][CMSALG] and
    the AES key wrap algorithm [AES-WRAP][RFC3394] can be applied to

Moriai, Kato                                                    [Page 8]

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    this document.  No security problem has been found on Camellia
    [CRYPTREC][NESSIE].

6. Intellectual Property Statement

    Mitsubishi Electric Corporation and Nippon Telegraph and Telephone
    Corporation have pending applications or filed patents which are
    essential to Camellia.  License policy for these essential patents
    will be available on the IETF page of Intellectual Property Rights
    Notices.


References
    [AES]   National Institute of Standards.
        FIPS Pub 197: Advanced Encryption Standard (AES). 26
        November 2001.

    [DES]   National Institute of Standards and Technology.
        FIPS Pub 46: Data Encryption Standard.  15 January 1977.

    [AES-WRAP] National Institute of Standards and Technology. AES Key
        Wrap Specification. 17 November 2001.
        http://csrc.nist.gov/encryption/kms/key-wrap.pdf

    [CamelliaID] J. Nakajima and S. Moriai, "A Description of the
        Camellia Encryption Algorithm", Internet-Draft, July 2001.
        draft-nakajima-camellia-02.txt

    [CamelliaSpec] K. Aoki, T. Ichikawa, M. Kanda, M. Matsui, S. Moriai,
        J. Nakajima, and T. Tokita "Specification of Camellia - a
        128-bit Block Cipher".  http://info.isl.ntt.co.jp/camellia/

    [CamelliaTech] K. Aoki, T. Ichikawa, M. Kanda, M. Matsui, S. Moriai,
        J. Nakajima, and T. Tokita "Camellia: A 128-Bit Block Cipher
        Suitable for Multiple Platforms - Design and Analysis -", In
        Selected Areas in Cryptography, 7th Annual International
        Workshop, SAC 2000, August 2000, Proceedings, Lecture Notes in
        Computer Science 2012, pp.39--56, Springer-Verlag, 2001.

    [CMS] R. Housley, "Cryptographic Message Syntax", RFC 3369, August
        2002.

    [CMSALG] R. Housley, "Cryptographic Message Syntax (CMS)
        Algorithms", RFC 3370, August 2002.

    [CRYPTREC] Information-technology Promotion Agency (IPA), Japan,
        CRYPTREC. http://www.ipa.go.jp/security/enc/CRYPTREC/index-e.html

    [NESSIE] New European Schemes for Signatures, Integrity and
        Encryption (NESSIE) project. http://www.cryptonessie.org

    [RFC2119] S. Bradner, "Key words for use in RFCs to Indicate
        Requirement Levels", BCP 14, RFC 2119, March 1997.


Moriai, Kato                                                    [Page 9]

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    [RFC2633] Ramsdell, B., Editor.  S/MIME Version 3 Message
        Specification.  RFC 2633.  June 1999.

    [RFC3394] J. Schaad and R. Housley, "Advanced Encryption Standard
        (AES) Key Wrap Algorithm", RFC 3394, September 2002.


Authors' Address

    Shiho Moriai
    Nippon Telegraph and Telephone Corporation
    Phone: +81-468-59-2007
    FAX:   +81-468-59-3858
    Email: shiho@isl.ntt.co.jp

    Akihiro Kato
    NTT Software Corporation
    Phone: +81-45-212-7404
    FAX:   +81-45-212-7410
    Email: akato@po.ntts.co.jp

Appendix A  ASN.1 Module

DEFINITIONS IMPLICIT TAGS ::=
BEGIN

-- Camellia using CBC-chaining mode for key sizes of 128, 192, 256

id-camellia128-cbc OBJECT IDENTIFIER ::=
    { iso(1) member-body(2) 392 200011 61 security(1)
      algorithm(1) symmetric-encryption-algorithm(1)
      camellia128-cbc(2) }

id-camellia192-cbc OBJECT IDENTIFIER ::=
   { iso(1) member-body(2) 392 200011 61 security(1)
     algorithm(1) symmetric-encryption-algorithm(1)
     camellia192-cbc(3) }

id-camellia256-cbc OBJECT IDENTIFIER ::=
   { iso(1) member-body(2) 392 200011 61 security(1)
     algorithm(1) symmetric-encryption-algorithm(1)
     camellia256-cbc(4) }

-- Camellia-IV is a the parameter for all the above object identifiers.

Camellia-IV ::= OCTET STRING (SIZE(16))

-- Camellia S/MIME Capabilty parameter for all the above object
-- identifiers.

CamelliaSMimeCapability ::= NULL

-- Camellia Key Wrap Algorithm identifiers - Parameter is absent


Moriai, Kato                                                   [Page 10]

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id-camellia128-wrap OBJECT IDENTIFIER ::=
    { iso(1) member-body(2) 392 200011 61 security(1)
      algorithm(1) key-wrap-algorithm(3)
      camellia128-wrap(2) }

id-camellia192-wrap OBJECT IDENTIFIER ::=
    { iso(1) member-body(2) 392 200011 61 security(1)
      algorithm(1) key-wrap-algorithm(3)
      camellia192-wrap(3) }

id-camellia256-wrap OBJECT IDENTIFIER ::=
    { iso(1) member-body(2) 392 200011 61 security(1)
      algorithm(1) key-wrap-algorithm(3)
      camellia256-wrap(4) }


END





































Moriai, Kato                                                   [Page 11]


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