S/MIME Working Group                                          J.                  James Randall, Randall Consulting
     Internet Draft                                        Burt Kaliski, EMC
                                                          John Brainard, RSA
Document: draft-ietf-smime-cms-rsa-kem-06.txt                  B.Kaliski
                                                           Sean Turner, IECA
     Expires: January 7, 2010                            Category: Standards                                            EMC Corp.
Expires: March
                                                                July 7, 2009                                       September 2008

                  Use of the RSA-KEM Key Transport Algorithm in CMS
                 <draft-ietf-smime-cms-rsa-kem-06.txt>

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     Abstract

        The RSA-KEM Key Transport Algorithm is a one-pass (store-and-forward)
        mechanism for transporting keying data to a recipient using the
        recipient's RSA public key. This document specifies the conventions
        for using the RSA-KEM Key Transport Algorithm with the Cryptographic
        Message Syntax (CMS). The ASN.1 syntax is aligned with ANS X9.44 and
        ISO/IEC 18033-2.

     Conventions Used in This Document

        The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
        "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in this
        document are to be interpreted as described in RFC 2119 [STDWORDS].

     1. Introduction

        The RSA-KEM Key Transport Algorithm is a one-pass (store-and-forward)
        mechanism for transporting keying data to a recipient using the
        recipient's RSA public key.

        Most previous key transport algorithms based on the RSA public-key
        cryptosystem (e.g., the popular PKCS #1 v1.5 algorithm [PKCS1]) have
        the following general form:

        1. Format or "pad" the keying data to obtain an integer m.

        2. Encrypt the integer m with the recipient's RSA public key:

                                  c = m^e mod n

        3. Output c as the encrypted keying data.

        The RSA-KEM Key Transport Algorithm takes a different approach that
        provides higher security assurance, by encrypting a _random_ integer
        with the recipient's public key, and using a symmetric key-wrapping
        scheme to encrypt the keying data. It has the following form:

        1. Generate a random integer z between 0 and n-1.

        2. Encrypt the integer z with the recipient's RSA public key:

                                  c = z^e mod n. n

        3. Derive a key-encrypting key KEK from the integer z.

        4. Wrap the keying data using KEK to obtain wrapped keying data WK.

        5. Output c and WK as the encrypted keying data.

        This different approach provides higher security assurance because
        (a) the input to the underlying RSA operation is effectively a random
        integer between 0 and n-1, where n is the RSA modulus, so it does not
        have any structure that could be exploited by an adversary, and (b)
        the input is independent of the keying data so the result of the RSA
        decryption operation is not directly available to an adversary.  As a
        result, the algorithm enjoys a "tight" security proof in the random
        oracle model. (In other padding schemes, such as PKCS #1 v1.5, the
        input has structure and/or depends on the keying data, and the
        provable security assurances are not as strong.) The approach is also
        architecturally convenient because the public-key operations are
        separate from the symmetric operations on the keying data. One
        benefit is that the length of the keying data is bounded only by the
        symmetric key-wrapping scheme, not the size of the RSA modulus.

        The RSA-KEM Key Transport Algorithm in various forms is being adopted
        in several draft standards as well as in ANS-X9.44 and ISO/IEC
   18033-2. 18033-
        2. It has also been recommended by the NESSIE project [NESSIE].

           For completeness, a specification of the algorithm is given in
        Appendix A of this document; ASN.1 syntax is given in Appendix B.

        NOTE: The term KEM stands for "key encapsulation mechanism" and
        refers to the first three steps of the process above. The
        formalization of key transport algorithms (or more generally,
        asymmetric encryption schemes) in terms of key encapsulation
        mechanisms is described further in research by Victor Shoup leading
        to the development of the ISO/IEC 18033-2 standard [SHOUP].

     2. Use in CMS

        The RSA-KEM Key Transport Algorithm MAY be employed for one or more
        recipients in the CMS enveloped-data content type (Section 6 of
        [CMS]), where the keying data processed by the algorithm is the CMS
        content-encryption key.

        The RSA-KEM Key Transport Algorithm SHOULD be considered for new
        CMS-based applications as a replacement for the widely implemented
        RSA encryption algorithm specified originally in PKCS #1 v1.5 (see
        [PKCS1] and Section 4.2.1 of [CMSALGS]), which is vulnerable to
        chosen-ciphertext attacks. The RSAES-OAEP Key Transport Algorithm has
        also been proposed as a replacement (see [PKCS1] and [CMS-
   OAEP]). [CMS-OAEP]).
        RSA-KEM has the advantage over RSAES-OAEP of a tighter security
        proof, but the disadvantage of slightly longer encrypted keying data.

2.1

     2.1. Underlying Components

        A CMS implementation that supports the RSA-KEM Key Transport
        Algorithm MUST support at least the following underlying components:

      *

        o  For the key derivation function, KDF2 or KDF3 (see [ANS-X9.44] [ANS-X9.44]) (see
           [IEEE-P1363a]) based on SHA-1 (see [FIPS-180-2]) (this function is
           also specified as the key derivation function in
         [ANS-X9.63]).

      * [ANS-X9.63]), and
           KDF3 (see [IEEE-P1363a]) based on SHA-256 (see [FIPS-180-2]).

        o  For the key-wrapping scheme, AES-Wrap-128, i.e., the AES Key Wrap
           with a 128-bit key encrypting key (see [AES-WRAP])

        An implementation SHOULD also support KDF2 and KDF3 based on SHA-256
   (see [FIPS-180-2]). SHA-1 and KDF2
        based on SHA-256. The Camillia Camellia key wrap algorithm (see [CAMILLIA])
   should [CAMELLIA])
        SHOULD be supported, and, if 3DES is supported as a content-
        encryption cipher, then the Triple-DES Key Wrap (see [3DES-WRAP])
        SHOULD also be supported.

        It MAY support other underlying components. When AES or Camilla Camellia are
        used the data block size is 128 bits while the key size can be 128,
        192, or 256 bits while Triple DES requires a data block size of 64
        bits and a key size of 112 or 168 bits.

2.2

     2.2. RecipientInfo Conventions

        When the RSA-KEM Key Transport Algorithm is employed for a recipient,
        the RecipientInfo alternative for that recipient MUST be
        KeyTransRecipientInfo. The algorithm-specific fields of the
        KeyTransRecipientInfo value MUST have the following values:

      *

        o  keyEncryptionAlgorithm.algorithm MUST be id-ac-generic-hybrid
         (see id-rsa-kem see Appendix
           B)

      *

        o  keyEncryptionAlgorithm.parameters MUST be a value of type
           GenericHybridParameters, identifying the RSA-KEM key encapsulation
           mechanism (see Appendix B)

      *

        o  encryptedKey MUST be the encrypted keying data output by the
           algorithm, where the keying data is the content-encryption key.
         (see
           key.(see Appendix A)

2.3

     2.3. Certificate Conventions

        The conventions specified in this section augment RFC 3280 [PROFILE].

        A recipient who employs the RSA-KEM Key Transport Algorithm MAY
        identify the public key in a certificate by the same
        AlgorithmIdentifier as for the PKCS #1 v1.5 algorithm, i.e., using
        the rsaEncryption object identifier [PKCS1]. The fact that the user
        will accept RSA-KEM with this public key is not indicated by the use
        of this identifier.  This may be signed by the use of the appropriate
        SMIME Capabilities either in a message or in the certificate.

        If the recipient wishes only to employ the RSA-KEM Key Transport
        Algorithm with a given public key, the recipient MUST identify the
        public key in the certificate using the id-ac-generic-hybrid id-rsa-kem object identifier
        (see Appendix B) where the associated
   GenericHybridParameters value indicates the underlying components
   with which the algorithm is to be employed. B). The certificate user MUST
   perform the RSA-KEM Key Transport algorithm using only those
   components. parameters are absent.

        Regardless of the AlgorithmIdentifier used, the RSA public key is
        encoded in the same manner in the subject public key information. The
        RSA public key MUST be encoded using the type RSAPublicKey type:

            RSAPublicKey ::= SEQUENCE {
                modulus            INTEGER, -- n
                publicExponent     INTEGER  -- e
            }

        Here, the modulus is the modulus n, and publicExponent is the public
        exponent e. The DER encoded RSAPublicKey is carried in the
        subjectPublicKey BIT STRING within the subject public key
        information.

        The intended application for the key MAY be indicated in the key
        usage certificate extension (see [PROFILE], Section 4.2.1.3). If the
        keyUsage extension is present in a certificate that conveys an RSA
        public key with the id-ac-generic-hybrid id-rsa-kem object identifier as discussed above,
        then the key usage extension MUST contain the following value:

           keyEncipherment.

        dataEncipherment SHOULD NOT be present. That is, a key intended to be
        employed only with the RSA-KEM Key Transport Algorithm SHOULD NOT
        also be employed for data encryption or for authentication such as in
        signatures. Good cryptographic practice employs a given RSA key pair
        in only one scheme.  This practice avoids the risk that vulnerability
        in one scheme may compromise the security of the other, and may be
        essential to maintain provable security.

2.4

     2.4. SMIMECapabilities Attribute Conventions

        RFC 2633 3851 [MSG], 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. When constructing a
        signedData object, compliant software MAY include the
        SMIMECapabilities signed attribute announcing that it supports the
        RSA-KEM Key Transport algorithm.

        The SMIMECapability SEQUENCE representing the RSA-KEM Key Transport
        Algorithm MUST include the id-ac-generic-hybrid id-rsa-kem object identifier (see Appendix
        B) in the capabilityID field and MUST include a
        GenericHybridParameters value in the parameters field identifying the
        components with which the algorithm is to be employed.

        The DER encoding of a SMIMECapability SEQUENCE is the same as the DER
        encoding of an AlgorithmIdentifier. Example DER encodings for typical
        sets of components are given in Appendix B.4.

     3. Security Considerations

        The security of the RSA-KEM Key Transport Algorithm described in this
        document can be shown to be tightly related to the difficulty of
        either solving the RSA problem or breaking the underlying symmetric
        key-wrapping scheme, if the underlying key derivation function is
        modeled as a random oracle, and assuming that the symmetric key-wrapping key-
        wrapping scheme satisfies the properties of a data encapsulation
        mechanism [SHOUP]. While in practice a random-oracle result does not
        provide an actual security proof for any particular key derivation
        function, the result does provide assurance that the general
        construction is reasonable; a key derivation function would need to
        be particularly weak to lead to an attack that is not possible in the
        random oracle model.

        The RSA key size and the underlying components should be selected
        consistent with the desired symmetric security level for an
        application. Several security levels have been identified in [NIST-
        FIPS PUB 800-57]. For brevity, the first three levels are mentioned
        here:

      *

        o  80-bit security. The RSA key size SHOULD be at least 1024 bits,
           the hash function underlying the KDF SHOULD be SHA-1 or above, and
           the symmetric key-wrapping scheme SHOULD be AES Key Wrap,
         Triple-DES Triple-
           DES Key Wrap, or Camillia Camellia Key Wrap.

      *

        o  112-bit security. The RSA key size SHOULD be at least 2048 bits,
           the hash function underlying the KDF SHOULD be SHA-224 or above,
           and the symmetric key-wrapping scheme SHOULD be AES Key Wrap,
           Triple-DES Key Wrap, or Camillia Camellia Key Wrap.

      *

        o  128-bit security. The RSA key size SHOULD be at least 3072 bits,
           the hash function underlying the KDF SHOULD be SHA-256 or above,
           and the symmetric key-wrapping scheme SHOULD be AES Key Wrap or Camillia
           Camellia Key Wrap.

        Note that the AES Key Wrap or Camillia Camellia Key Wrap MAY be used at all
        three of these levels; the use of AES or Camillia Camellia does not require a
        128-bit security level for other components.

        Implementations MUST protect the RSA private key and the content-
        encryption key. Compromise of the RSA private key may result in the
        disclosure of all messages protected with that key. Compromise of the
        content-encryption key may result in disclosure of the associated
        encrypted content.

        Additional considerations related to key management may be found in
        [NIST-GUIDELINE].

        The security of the algorithm also depends on the strength of the
        random number generator, which SHOULD have a comparable security
        level. For further discussion on random number generation, please see
        [RANDOM].

        Implementations SHOULD NOT reveal information about intermediate
        values or calculations, whether by timing or other "side channels",
        or otherwise an opponent may be able to determine information about
        the keying data and/or the recipient's private key. Although not all
        intermediate information may be useful to an opponent, it is
        preferable to conceal as much information as is practical, unless
        analysis specifically indicates that the information would not be
        useful.

        Generally, good cryptographic practice employs a given RSA key pair
        in only one scheme.  This practice avoids the risk that vulnerability
        in one scheme may compromise the security of the other, and may be
        essential to maintain provable security.  While RSA public keys have
        often been employed for multiple purposes such as key transport and
        digital signature without any known bad interactions, for increased
        security assurance, such combined use of an RSA key pair is NOT
        RECOMMENDED in the future (unless the different schemes are
        specifically designed to be used together).

        Accordingly, an RSA key pair used for the RSA-KEM Key Transport
        Algorithm SHOULD NOT also be used for digital signatures. (Indeed,
        ASC X9 requires such a separation between key establishment key pairs
        and digital signature key pairs.) Continuing this principle of key
        separation, a key pair used for the RSA-KEM Key Transport Algorithm
        SHOULD NOT be used with other key establishment schemes, or for data
        encryption, or with more than one set of underlying algorithm
        components.

        Parties MAY formalize the assurance that one another's
        implementations are correct through implementation validation, e.g.
        NIST's Cryptographic Module Validation Program (CMVP).

     4. References

4.1

     4.1. Normative References

        [3DES-WRAP]         Housley, R. Triple-DES and RC2 Key Wrapping. RFC
                            3217. December 2001.

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

        [ANS-X9.63]         American National Standard X9.63-2002: Public Key
                            Cryptography for the Financial Services Industry:
                            Key Agreement and Key Transport Using Elliptic
                            Curve Cryptography.

   [CAMILLIA]

        [CAMELLIA]          Kato, A., Moriai, S., and Kanda, M.: The Use of the
                            Camellia
                     Cipher Encryption Algorithm and Its Use With IPsec. in Cryptographic
                            Message Syntax. RFC 3657. December 2005.

        [CMS]               Housley, R. Cryptographic Message Syntax. RFC
                            3852. July 2004.

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

        [FIPS-180-2]        National Institute of Standards and Technology
                            (NIST). FIPS 180-2: Secure Hash Standard. August
                            2002.

        [MSG]               Ramsdell, B. S/MIME Version 3 Message
                            Specification. RFC 3851. July 2004.

        [PROFILE]           Cooper, D., Santesson, S., Farrell, S.,
                            Boeyen, S., Housley, R., Polk, W., Ford, W. and D. Solo. W. Polk. Internet
                            X.509 Public Key Infrastructure: Infrastructure Certificate
                            and Certificate Revocation List (CRL) Profile.
                            RFC 3280. April 2002. 5280. May 2008.

        [STDWORDS]          Bradner, S. Key Words for Use in RFCs to Indicate
                            Requirement Levels. RFC 2119. March 1997.

4.2

     4.2. Informative References

        [ANS-X9.44]         ASC X9F1 Working Group. American National
                            Standard X9.44: Public Key Cryptography for the
                            Financial Services Industry -- Key Establishment
                            Using Integer Factorization Cryptography. 2007

        [CMS-OAEP]          Housley, R. Use of the RSAES-OAEP Key Transport
                            Algorithm in the Cryptographic Message Syntax
                           (CMS). RFC 3560. July 2003.

        [IEEE-P1363a]       IEEE Std 1363a-2004: Standard Specifications for
                            Public Key Cryptography: Additional Techniques.
                            IEEE, 2004.

        [ISO-IEC-18033-2]   ISO/IEC 18033-2:2005 Information technology --
                            Security techniques -- Encryption algorithms --
                            Part 2: Asymmetric Ciphers. ISO/IEC, 2005.

        [NESSIE]            NESSIE Consortium. Portfolio of Recommended
                            Cryptographic Primitives. February 27, 2003.
                            Available via http://www.cryptonessie.org/.

        [NIST-GUIDELINE]    National Institute of Standards and Technology.
                            Special Publication 800-57: Recommendation for
                            Key Management. Part 1: General Guideline.
                            August 2005. Available via:
                            http://csrc.nist.gov/publications/index.html.

        [PKCS1]             Jonsson, J. and B. Kaliski. PKCS #1: RSA
                            Cryptography Specifications Version 2.1. RFC
                            3447. February 2003.

        [RANDOM]            Eastlake, D., S. Crocker, and J. Schiller.
                            Randomness Recommendations for Security. RFC
                            4086. June 2005.

        [SHOUP]             Shoup, V. A Proposal for an ISO Standard for
                            Public Key Encryption. Version 2.1, December 20,
                            2001. Available via http://www.shoup.net/papers/.

5. IANA Considerations

   Within the CMS, algorithms are identified by object identifiers
   (OIDs). With one exception, all of the OIDs used in this document
   were assigned in other IETF documents, in ISO/IEC standards
   documents, by the National Institute of Standards and Technology
   (NIST), and in Public-Key Cryptography Standards (PKCS) documents.
   The one exception is that the ASN.1 module's identifier (see Appendix
   B.3) is assigned in this document. No further action by the IANA is
   necessary for this document or any anticipated updates.

6. Acknowledgments

   This document is one part of a strategy to align algorithm standards
   produced by ASC X9, ISO/IEC JTC1 SC27, NIST, and the IETF. We would
   like to thank the members of the ASC X9F1 working group for their
   contributions to drafts of ANS X9.44 which led to this specification.
   Our thanks to Russ Housley as well for his guidance and
   encouragement. We also appreciate the helpful direction we've
   received from Blake Ramsdell and Jim Schaad in bringing this document
   to fruition. A special thanks to Magnus Nystrom for his assistance on
   Appendix B.

7. Authors' Addresses

   James Randall
   RSA, The Security Division of EMC
   174 Middlesex Turnpike
   Bedford, MA  01730
   USA
   e-mail:   jrandall@rsa.com

   Burt Kaliski
   EMC
   176 South Street
   Hopkinton, MA 01748
   USA
   e-mail:  kaliski_burt@emc.com

Appendix A. RSA-KEM Key Transport Algorithm

   The RSA-KEM Key Transport Algorithm is a one-pass (store-and-forward)
   mechanism for transporting keying data to a recipient using

     Appendix A.
                RSA-KEM Key Transport Algorithm

        The RSA-KEM Key Transport Algorithm is a one-pass (store-and-forward)
        mechanism for transporting keying data to a recipient using the
        recipient's RSA public key.

        With this type of algorithm, a sender encrypts the keying data using
        the recipient's public key to obtain encrypted keying data. The
        recipient decrypts the encrypted keying data using the recipient's
        private key to recover the keying data.

A.1

     A.1. Underlying Components

        The algorithm has the following underlying components:

       *

        o  KDF, a key derivation function, which derives keying data of a
           specified length from a shared secret value

       *

        o  Wrap, a symmetric key-wrapping scheme, which encrypts keying
         data Data
           using a key-encrypting key

        In the following, kekLen denotes the length in bytes of the key-
        encrypting key for the underlying symmetric key-wrapping scheme.

        In this scheme, the length of the keying data to be transported MUST
        be among the lengths supported by the underlying symmetric key-
        wrapping scheme. (Both the AES and Camillia Camellia Key Wraps, for instance,
        require the length of the keying data to be a multiple of 8 bytes,
        and at least 16 bytes.) Usage and formatting of the keying data
        (e.g., parity adjustment for Triple-DES keys) is outside the scope of
        this algorithm. With some key derivation functions, it is possible to
        include other information besides the shared secret value in the
        input to the function. Also, with some symmetric key-wrapping
        schemes, it is possible to associate a label with the keying data.
        Such uses are outside the scope of this document, as they are not
        directly supported by CMS.

A.2

     A.2. Sender's Operations

        Let (n,e) be the recipient's RSA public key (see [PKCS1] for
        details) and let K be the keying data to be transported.

        Let nLen denote the length in bytes of the modulus n, i.e., the least
        integer such that 2^{8*nLen} > n.

        The sender performs the following operations:

        1. Generate a random integer z between 0 and n-1 (see Note), and
           convert z to a byte string Z of length nLen, most significant byte
           first:

               z = RandomInteger (0, n-1)
               Z = IntegerToString (z, nLen)

        2. Encrypt the random integer z using the recipient's public key
         (n,e) n,e)
           and convert the resulting integer c to a ciphertext C, a byte
           string of length nLen:

               c = z^e mod n
               C = IntegerToString (c, nLen)

        3. Derive a key-encrypting key KEK of length kekLen bytes from the
           byte string Z using the underlying key derivation function:

               KEK = KDF (Z, kekLen)

        4. Wrap the keying data K with the key-encrypting key KEK using the
           underlying key-wrapping scheme to obtain wrapped keying data WK:

               WK = Wrap (KEK, K)

        5. Concatenate the ciphertext C and the wrapped keying data WK to
           obtain the encrypted keying data EK:

               EK = C || WK

        6. Output the encrypted keying data EK.

        NOTE: The random integer z MUST be generated independently at random
        for different encryption operations, whether for the same or
        different recipients.

A.3

     A.3. Recipient's Operations

        Let (n,d) be the recipient's RSA private key (see [PKCS1]; other
        private key formats are allowed) and let EK be the encrypted keying
        data.

        Let nLen denote the length in bytes of the modulus n.

        The recipient performs the following operations:

        1. Separate the encrypted keying data EK into a ciphertext C of
           length nLen bytes and wrapped keying data WK:

               C || WK = EK

           If the length of the encrypted keying data is less than nLen
           bytes, output "decryption error" and stop.

        2. Convert the ciphertext C to an integer c, most significant byte
           first. Decrypt the integer c using the recipient's private key
           (n,d) to recover an integer z (see Note):

               c = StringToInteger (C)
               z = c^d mod n

           If the integer c is not between 0 and n-1, output "decryption
           error" and stop.

        3. Convert the integer z to a byte string Z of length nLen, most
           significant byte first (see Note):

               Z = IntegerToString (z, nLen)

        4. Derive a key-encrypting key KEK of length kekLen bytes from
           the byte string Z using the underlying key derivation function
           (see Note):

               KEK = KDF (Z, kekLen)

        5. Unwrap the wrapped keying data WK with the key-encrypting key
           KEK using the underlying key-wrapping scheme to recover the
           keying data K:

              K = Unwrap (KEK, WK)

           If the unwrapping operation outputs an error, output "decryption
           error" and stop.

        6. Output the keying data K.

        NOTE: Implementations SHOULD NOT reveal information about the integer
        z and the string Z, nor about the calculation of the exponentiation
        in Step 2, the conversion in Step 3, or the key derivation in Step 4,
        whether by timing or other "side channels". The observable behavior
        of the implementation SHOULD be the same at these steps for all
        ciphertexts C that are in range. (For example, IntegerToString
        conversion should take the same amount of time regardless of the
        actual value of the integer z.) The integer z, the string Z and other
        intermediate results MUST be securely deleted when they are no longer
        needed.

     Appendix B.
                ASN.1 Syntax

        The ASN.1 syntax for identifying the RSA-KEM Key Transport Algorithm
        is an extension of the syntax for the "generic hybrid cipher" in
        ISO/IEC 18033-2 [ISO-IEC-18033-2], and is the same as employed in ANS
        X9.44 [ANS-X9.44]. The syntax for the scheme is given in Section B.1.
        The syntax for selected underlying components including those
        mentioned above is given in B.2.

        The following object identifier prefixes are used in the definitions
        below:

           is18033-2 OID ::= { iso(1) standard(0) is18033(18033) part2(2) }

           nistAlgorithm OID ::= {
              joint-iso-itu-t(2) country(16) us(840) organization(1)
              gov(101) csor(3) nistAlgorithm(4)
           }

           pkcs-1 OID ::= {
              iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-1(1)
           }

        NullParms is a more descriptive synonym for NULL when an algorithm
        identifier has null parameters:

           NullParms ::= NULL

        The material in this Appendix is based on ANS X9.44.

     B.1 RSA-KEM Key Transport Algorithm

        The object identifier for the RSA-KEM Key Transport Algorithm is the
   same as for the "generic hybrid cipher" in ISO/IEC 18033-2,
   id-ac-generic-hybrid, id-
        rsa-kem, which is defined in the draft as:

      id-ac-generic-hybrid

            id-rsa-kem OID ::= {
         is18033-2 asymmetric-cipher(1) generic-hybrid(2)
              iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1)
              pkcs-9(9) smime(16) alg(3) TBA
            }

   The associated

        When id-rsa-kem is used in an AlgorithmIdentifier, the parameters for id-ac-generic-hybrid have type
   GenericHybridParameters:
        MUST employ the GenericHybridParameters syntax. The parameters MUST
        be absent when used in the subjectPublicKeyInfo field The syntax for
        GenericHybridParameters is as follows:

           GenericHybridParameters ::= {
              kem  KeyEncapsulationMechanism,
              dem  DataEncapsulationMechanism
           }

        The fields of type GenericHybridParameters have the following
        meanings:

      *

        o  kem identifies the underlying key encapsulation mechanism. For the
           RSA-KEM Key Transport Algorithm, the scheme is RSA-KEM from
           ISO/IEC 18033-2.

           The object identifier for RSA-KEM (as a key encapsulation
           mechanism) is id-kem-rsa, which is defined in ISO/IEC 18033-2 as

              id-kem-rsa OID ::= {
                 is18033-2 key-encapsulation-mechanism(2) rsa(4)
              }

           The associated parameters for id-kem-rsa have type
           RsaKemParameters:

              RsaKemParameters ::= {
                 keyDerivationFunction  KeyDerivationFunction,
                 keyLength              KeyLength
              }

           The fields of type RsaKemParameters have the following meanings:

                   *  keyDerivationFunction identifies the underlying key
                      derivation function. For alignment with ANS X9.44, it
                      MUST be KDF2 or KDF3. However, other key derivation
                      functions MAY be used with CMS. Please see B.2.1 for
                      the syntax for KDF2 and KDF3.

                         KeyDerivationFunction ::=
                            AlgorithmIdentifier {{KDFAlgorithms}}

                         KDFAlgorithms ALGORITHM ::= {
                            kdf2 | kdf3,
                            ...  -- implementations may define other methods
                         }

                   *  keyLength is the length in bytes of the key-encrypting
                      key, which depends on the underlying symmetric key-
                      wrapping scheme.

                         KeyLength ::= INTEGER (1..MAX)

      *
        o  dem identifies the underlying data encapsulation mechanism. For
           alignment with ANS X9.44, it MUST be an X9-approved symmetric key-wrapping key-
           wrapping scheme. (See Note.) However, other symmetric key-wrapping
           schemes MAY be used with CMS. Please see B.2.2 for the syntax for
           the AES, Triple-DES, and Camillia Camellia Key Wraps.

              DataEncapsulationMechanism ::=
                 AlgorithmIdentifier {{DEMAlgorithms}}

              DEMAlgorithms ALGORITHM ::= {
                 X9-SymmetricKeyWrappingSchemes,
               Camillia-KeyWrappingSchemes,
                 Camellia-KeyWrappingSchemes,
                 ...  -- implementations may define other methods
              }

              X9-SymmetricKeyWrappingSchemes ALGORITHM ::= {
                 aes128-Wrap | aes192-Wrap | aes256-Wrap | tdes-Wrap,
                 ...   -- allows for future expansion
              }

            Camillia-KeyWrappingSchemes

              Camellia-KeyWrappingSchemes ALGORITHM ::= {
               camillia128-Wrap
                 Camellia128-Wrap | camillia192-Wrap Camellia192-Wrap | camillia256-Wrap Camellia256-Wrap
              }

           NOTE: The generic hybrid cipher in ISO/IEC 18033-2 can encrypt
        arbitrary data, hence the term "data encapsulation mechanism". The
        symmetric key-wrapping schemes take the role of data encapsulation
        mechanisms in the RSA-KEM Key Transport Algorithm.  ISO/IEC 18033-2
        allows only three specific data encapsulation mechanisms, not
        including any of these symmetric key-wrapping schemes. However, the
        ASN.1 syntax in that document expects that additional algorithms will
        be allowed.

     B.2 Selected Underlying Components

     B.2.1 Key Derivation Functions

        The object identifier for KDF2 (see [ANS X9.44]) is:

           id-kdf-kdf2 OID ::= { x9-44-components kdf2(1) }

        The associated parameters identify the underlying hash function. For
        alignment with ANS X9.44, the hash function MUST be an ASC
   X9-approved X9-
        approved hash function. However, other hash functions MAY be used
        with CMS.

              kdf2 ALGORITHM ::= { OID id-kdf-kdf2  PARMS KDF2-HashFunction }
              KDF2-HashFunction ::= AlgorithmIdentifier {{KDF2-HashFunctions}} {{KDF2-
        HashFunctions}}

              KDF2-HashFunctions ALGORITHM ::= {
                 X9-HashFunctions,
                 ...  -- implementations may define other methods
              }

              X9-HashFunctions ALGORITHM ::= {
                 sha1 | sha224 | sha256 | sha384 | sha512,
                 ...  -- allows for future expansion
              }

        The object identifier for SHA-1 is

              id-sha1 OID ::= {
                 iso(1) identified-organization(3) oiw(14) secsig(3)
                 algorithms(2) sha1(26)
              }

        The object identifiers for SHA-224, SHA-256, SHA-384 and SHA-512 are

              id-sha224 OID ::= { nistAlgorithm hashAlgs(2) sha224(4) }
              id-sha256 OID ::= { nistAlgorithm hashAlgs(2) sha256(1) }
              id-sha384 OID ::= { nistAlgorithm hashAlgs(2) sha384(2) }
              id-sha512 OID ::= { nistAlgorithm hashAlgs(2) sha512(3) }

        There has been some confusion over whether the various SHA object
        identifiers have a NULL parameter, or no associated parameters. As
        also discussed in [PKCS1], implementations SHOULD generate algorithm
        identifiers without parameters, and MUST accept algorithm identifiers
        either without parameters, or with NULL parameters.

              sha1   ALGORITHM ::= { OID id-sha1   } -- NULLParms MUST be
              sha224 ALGORITHM ::= { OID id-sha224 } -- accepted for these
              sha256 ALGORITHM ::= { OID id-sha256 } -- OIDs
              sha384 ALGORITHM ::= { OID id-sha384 } -- ""
              sha512 ALGORITHM ::= { OID id-sha512 } -- ""

        The object identifier for KDF3 (see [ANS X9.44]) is:

              id-kdf-kdf3 OID ::= { x9-44-components kdf3(2) }
        The associated parameters identify the underlying hash function. For
        alignment with the draft ANS X9.44, the hash function MUST be an ASC
        X9-approved hash function. (See Note.) However, other hash functions
        MAY be used with CMS.

           kdf3 ALGORITHM ::= { OID id-kdf-kdf3  PARMS KDF3-HashFunction }

           KDF3-HashFunction ::= AlgorithmIdentifier { KDF3-HashFunctions }

           KDF3-HashFunctions ALGORITHM ::= {
              X9-HashFunctions,
              ...  -- implementations may define other methods
           }

     B.2.2 Symmetric Key-Wrapping Schemes

        The object identifiers for the AES Key Wrap depends on the size of
        the key encrypting key. There are three object identifiers (see
        [AES-WRAP]):

           id-aes128-Wrap OID ::= { nistAlgorithm aes(1) aes128-Wrap(5)  }
           id-aes192-Wrap OID ::= { nistAlgorithm aes(1) aes192-Wrap(25) }
           id-aes256-Wrap OID ::= { nistAlgorithm aes(1) aes256-Wrap(45) }

        These object identifiers have no associated parameters.

           aes128-Wrap ALGORITHM ::= { OID id-aes128-Wrap }
           aes192-Wrap ALGORITHM ::= { OID id-aes192-Wrap }
           aes256-Wrap ALGORITHM ::= { OID id-aes256-Wrap }

        The object identifier for the Triple-DES Key Wrap (see [3DES-WRAP])
        is

           id-alg-CMS3DESwrap OBJECT IDENTIFIER ::= {
              iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
              smime(16) alg(3) 6
           }

        This object identifier has a NULL parameter.

           tdes-Wrap ALGORITHM ::=
              { OID id-alg-CMS3DESwrap  PARMS NullParms }

        NOTE: As of this writing, the AES Key Wrap and the Triple-DES Key
        Wrap are in the process of being approved by ASC X9.

        The object identifiers for the Camillia Camellia Key Wrap depends depend on the size
        of the key encrypting key. There are three object identifiers:

           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) }

         These object identifiers have no associated parameters.

           camellia128-Wrap ALGORITHM ::= { OID id-camellia128-Wrap }
           camellia192-Wrap ALGORITHM ::= { OID id-camellia192-Wrap }
           camellia256-Wrap ALGORITHM ::= { OID id-camellia256-Wrap }

     B.3 ASN.1 module

        CMS-RSA-KEM
           { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1)
             pkcs-9(9) smime(16) modules(0) cms-rsa-kem(21) }

        DEFINITIONS ::=

        BEGIN

           -- EXPORTS ALL

           -- IMPORTS None

           -- Useful types and definitions

           OID ::= OBJECT IDENTIFIER  -- alias

           -- Unless otherwise stated, if an object identifier has associated

           -- parameters (i.e., the PARMS element is specified), the parameters
           -- parameters field shall be included in algorithm identifier
           -- values. The
   -- parameters field shall be omitted if and only if
           -- the object
   -- identifier does not have associated parameters
           -- (i.e., the PARMS
   -- element is omitted), unless otherwise stated.

           ALGORITHM ::= CLASS {
              &id    OBJECT IDENTIFIER  UNIQUE,
              &Type  OPTIONAL
           }
           WITH SYNTAX { OID &id [PARMS &Type] }

           AlgorithmIdentifier { ALGORITHM:IOSet } ::= SEQUENCE {
              algorithm   ALGORITHM.&id( {IOSet} ),
              parameters  ALGORITHM.&Type( {IOSet}{@algorithm} )  OPTIONAL
           }

           NullParms ::= NULL

           -- ISO/IEC 18033-2 arc

           is18033-2 OID ::= { iso(1) standard(0) is18033(18033) part2(2) }

           -- NIST algorithm arc

           nistAlgorithm OID ::= {
              joint-iso-itu-t(2) country(16) us(840) organization(1)
              gov(101) csor(3) nistAlgorithm(4)
           }

           -- PKCS #1 arc

           pkcs-1 OID ::= {
             iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-1(1)
           }

           -- RSA-KEM Key Transport Algorithm, based on Generic Hybrid Cipher

   id-ac-generic-hybrid Algorithm

            id-rsa-kem OID ::= {
      is18033-2 asymmetric-cipher(1) generic-hybrid(2)
              iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1)
              pkcs-9(9) smime(16) alg(3) TBA
            }

           GenericHybridParameters ::= SEQUENCE {
              kem  KeyEncapsulationMechanism,
              dem  DataEncapsulationMechanism
           }

          KeyEncapsulationMechanism ::= AlgorithmIdentifier {{KEMAlgorithms}}

   KEMAlgorithms ALGORITHM ::= {
   ... -- Don't know what you want in here
   }
          id-kem-rsa OID ::= {
             is18033-2 key-encapsulation-mechanism(2) rsa(4)
          }

          RsaKemParameters ::= SEQUENCE {
             keyDerivationFunction  KeyDerivationFunction,
             keyLength              KeyLength
          }

          KeyDerivationFunction ::= AlgorithmIdentifier {{KDFAlgorithms}}

          KDFAlgorithms ALGORITHM ::= {
             kdf2 | kdf3,
             ...  -- implementations may define other methods
          }

          KeyLength ::= INTEGER (1..MAX)

          DataEncapsulationMechanism ::=
             AlgorithmIdentifier {{DEMAlgorithms}}

          DEMAlgorithms ALGORITHM ::= {
             X9-SymmetricKeyWrappingSchemes |
      Camillia-KeyWrappingSchemes,
             Camellia-KeyWrappingSchemes,
             ...  -- implementations may define other methods
          }

          X9-SymmetricKeyWrappingSchemes ALGORITHM ::= {
             aes128-Wrap | aes192-Wrap | aes256-Wrap | tdes-Wrap,
             ...   -- allows for future expansion
          }

          X9-SymmetricKeyWrappingScheme ::=
             AlgorithmIdentifier {{ X9-SymmetricKeyWrappingSchemes }}

   Camillia-KeyWrappingSchemes

          Camellia-KeyWrappingSchemes ALGORITHM ::= {
             camellia128-Wrap | camellia192-Wrap | camellia256-Wrap,
             ... -- allows for future expansion
          }

   Camillia-KeyWrappingScheme

          Camellia-KeyWrappingScheme ::=
             AlgorithmIdentifier {{ Camillia-KeyWrappingSchemes Camellia-KeyWrappingSchemes }}

          -- Key Derivation Functions

          id-kdf-kdf2 OID ::= { x9-44-components kdf2(1) }
          -- Base arc

          x9-44 OID ::= {
             iso(1) identified-organization(3) tc68(133) country(16) x9(840)
             x9Standards(9) x9-44(44)
          }

          x9-44-components OID ::= { x9-44 components(1) }

          kdf2 ALGORITHM ::= { OID id-kdf-kdf2  PARMS KDF2-HashFunction }

          KDF2-HashFunction ::= AlgorithmIdentifier {{ KDF2-HashFunctions }}

          KDF2-HashFunctions ALGORITHM ::= {
             X9-HashFunctions,
             ...  -- implementations may define other methods
          }

          -- id-kdf-kdf3 OID ::= { x9-44-components kdf3(2) } kdf3 ALGORITHM
        ::= { OID id-kdf-kdf2  PARMS KDF3-HashFunction } KDF3-HashFunction
        ::= AlgorithmIdentifier {{ KDF3-HashFunctions }}

          KDF3-HashFunctions ALGORITHM ::= {
              X9-HashFunctions,
              ...  -- implementations may define other methods
          }

          -- Hash Functions

          X9-HashFunctions ALGORITHM ::= {
             sha1 | sha224 | sha256 | sha384 | sha512,
             ...  -- allows for future expansion
          }

          id-sha1 OID ::= {
             iso(1) identified-organization(3) oiw(14) secsig(3)
             algorithms(2) sha1(26)
          }

          id-sha224 OID ::= { nistAlgorithm hashAlgs(2) sha256(4) }
          id-sha256 OID ::= { nistAlgorithm hashAlgs(2) sha256(1) }
          id-sha384 OID ::= { nistAlgorithm hashAlgs(2) sha384(2) }
          id-sha512 OID ::= { nistAlgorithm hashAlgs(2) sha512(3) }
          sha1   ALGORITHM ::= { OID id-sha1    } -- NullParms MUST be
          sha224 ALGORITHM ::= { OID id-sha224  } -- accepted for these
          sha256 ALGORITHM ::= { OID id-sha256  } -- OIDs
          sha384 ALGORITHM ::= { OID id-sha384  } -- ""
          sha512 ALGORITHM ::= { OID id-sha512  } -- ""

           -- Symmetric Key-Wrapping Schemes

          id-aes128-Wrap OID ::= { nistAlgorithm aes(1) aes128-Wrap(5)  }
          id-aes192-Wrap OID ::= { nistAlgorithm aes(1) aes192-Wrap(25) }
          id-aes256-Wrap OID ::= { nistAlgorithm aes(1) aes256-Wrap(45) }

          aes128-Wrap ALGORITHM ::= { OID id-aes128-Wrap }
          aes192-Wrap ALGORITHM ::= { OID id-aes192-Wrap }
          aes256-Wrap ALGORITHM ::= { OID id-aes256-Wrap }

          id-alg-CMS3DESwrap OBJECT IDENTIFIER ::= {
             iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
             smime(16) alg(3) 6
          }

          tdes-Wrap ALGORITHM ::= { OID id-alg-CMS3DESwrap  PARMS NullParms }

          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) }

          camellia128-Wrap ALGORITHM ::= { OID id-camellia128-Wrap }
          camellia192-Wrap ALGORITHM ::= { OID id-camellia192-Wrap }
          camellia256-Wrap ALGORITHM ::= { OID id-camellia256-Wrap }

        END
     B.4 Examples

        As an example, if the key derivation function is KDF2 based on
   SHA-256 onSHA-256
        and the symmetric key-wrapping scheme is the AES Key Wrap with a 128-bit 128-
        bit KEK, the AlgorithmIdentifier for the RSA-KEM Key Transport
        Algorithm will have the following value:

           SEQUENCE {
         id-ac-generic-hybrid,
              id-rsa-kem,                                   -- generic RSA-KEM cipher
              SEQUENCE {                           -- GenericHybridParameters
                 SEQUENCE {                    -- key encapsulation mechanism
                    id-kem-rsa,                                    -- RSA-KEM
                    SEQUENCE {                            -- RsaKemParameters
                       SEQUENCE {                  -- key derivation function
                          id-kdf-kdf2,                                -- KDF2
                          SEQUENCE {                     -- KDF2-HashFunction
                             id-sha256  -- SHA-256; no parameters (preferred)
                          },
                       16                              -- KEK length in bytes
                       },
                 SEQUENCE {                   -- data encapsulation mechanism
                    id-aes128-Wrap             -- AES-128 Wrap; no parameters
                 }
              }
           }

           This AlgorithmIdentifier value has the following DER encoding: encoding (??
        indicates the algorithm number which is to be assigned):

             30 4f 53
                06 07 28 81 8c 71 02 0b 2a 86 48 86 f7 0d 01 02 09 10 03 ??         -- id-ac-generic-hybrid id-rsa-kem
                30 44
                   30 25
                      06 07 28 81 8c 71 02 02 04               -- id-kem-rsa
                      30 1a
                         30 16
                            06 07 28 81 8c 71 02 05 02        -- id-kdf-kdf2
                            30 0b
                               06 09 60 86 48 01 65 03 04 02 01 -- id-sha256
                         02 10                                   -- 16 bytes
                   30 0b
                      06 09 60 86 48 01 65 03 04 01 05     -- id-aes128-Wrap
        The DER encodings for other typical sets of underlying components are
        as follows:

         *

        o     KDF2 based on SHA-384, AES Key Wrap with a 192-bit KEK

              30 4f 46 06 07 28 81 8c 71 0b 2a 86 48 86 f7 0d 01 09 10 03 ?? 02
              01 02 30 44 30 25 06 07 28 81 8c 71 02 02 04 30
              1a 30 16 06 07 28 81 8c 71 02 05 02 30 0b 06 09
              60 86 48 01 65 03 04 02 02 02 18 30 0b 06 09 60
              86 48 01 65 03 04 01 19

         *

        o     KDF2 based on SHA-512, AES Key Wrap with a 256-bit KEK

              30 4f 46 06 07 28 81 8c 71 0b 2a 86 48 86 f7 0d 01 09 10 03 ?? 02
              01 02 30 44 30 25 06 07 28 81 8c 71 02 02 04 30
              1a 30 16 06 07 28 81 8c 71 02 05 02 30 0b 06 09
              60 86 48 01 65 03 04 02 03 02 20 30 0b 06 09 60
              86 48 01 65 03 04 01 2d

         *

        o  KDF2 based on SHA-1, Triple-DES Key Wrap with a 128-bit KEK
            (two-key (two-
           key triple-DES)

              30 4f 46 06 07 28 81 8c 71 0b 2a 86 48 86 f7 0d 01 09 10 03 ?? 02
              01 02 30 44 30 21 06 07 28 81 8c 71 02 02 04 30
              16 30 12 06 07 28 81 8c 71 02 05 02 30 07 06 05
              2b 0e 03 02 1a 02 10 30 0f 06 0b 2a 86 48 86 f7
              0d 01 09 10 03 06 05 00

Full Copyright Statement

   Copyright (C) The IETF Trust (2008).

   This document and translations

     IANA Considerations

        Within the CMS, algorithms are identified by object identifiers
        (OIDs). With one exception, all of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist the OIDs used in its implementation may be prepared, copied, published
   and distributed, this document
        were assigned in whole or other IETF documents, in part, without restriction ISO/IEC standards
        documents, by the National Institute of any
   kind, provided Standards and Technology
        (NIST), and in Public-Key Cryptography Standards (PKCS) documents.
        The one exception is that the above copyright notice and ASN.1 module's identifier (see Appendix
        B.3) is assigned in this paragraph
   are included on all such copies and derivative works.  However, document. No further action by the IANA is
        necessary for this document itself may not be modified in or any way, such as anticipated updates.

     Acknowledgments

        This document is one part of a strategy to align algorithm standards
        produced by removing ASC X9, ISO/IEC JTC1 SC27, NIST, and the copyright notice or references IETF. We would
        like to thank the Internet Society or other
   Internet organizations, except as needed for the purpose members of
   developing Internet standards in which case the procedures ASC X9F1 working group for
   copyrights defined in the Internet Standards process must be
   followed, or as required their
        contributions to translate it into languages other than
   English.

   The limited permissions granted above are perpetual drafts of ANS X9.44 which led to this specification.

        Our thanks to Russ Housley as well for his guidance and will not be
   revoked by
        encouragement. We also appreciate the Internet Society or its successors or assigns.

Disclaimer Statement

   This document helpful direction we've
        received from Blake Ramsdell and the information contained herein are provided on an
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
   THE INTERNET ENGINEERING TASK FORCE DISCLAIM 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 Jim Schaad in bringing this document
        to fruition. A PARTICULAR PURPOSE. special thanks to Magnus Nystrom for his assistance on
        Appendix B. Thanks also to Bob Griffin and John Linn for both
        editorial direction and procedural guidance.

     Author Information

        James Randall

        Randall Consulting
        55 Sandpiper Drive
        Dover, NH 03820
        USA

        Email:  jdrandall@comcast.net

        Burt Kaliski

        EMC
        176 South Street
        Hopkinton, MA 01748
        USA

        Email:  kaliski_burt@emc.com

        John Brainard

        RSA, The Security Division of EMC
        174 Middlesex Turnpike
        Bedford, MA  01730
        USA
        Email:   jbrainard@rsa.com

        Sean Turner

        IECA, Inc.
        3057 Nutley Street, Suite 106
        Fairfax, VA 22031
        USA

        Email: turners@ieca.com