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Versions: 00 01 02 RFC 5008

INTERNET DRAFT                                                R. Housley
                                                          Vigil Security
Expires December 2007                                         J. Solinas
June 2007                                                            NSA


    Suite B in Secure/Multipurpose Internet Mail Extensions (S/MIME)
                  <draft-housley-smime-suite-b-02.txt>


Status of this Memo

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Abstract

   This document specifies the conventions for using the United States
   National Security Agency's Suite B algorithms in Secure/Multipurpose
   Internet Mail Extensions (S/MIME) as specified in RFC 3851.













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1.  Introduction

   This document specifies the conventions for using the United States
   National Security Agency's Suite B algorithms [SuiteB] in
   Secure/Multipurpose Internet Mail Extensions (S/MIME) [MSG].  S/MIME
   makes use of the Cryptographic Message Syntax (CMS) [CMS].  In
   particular, the signed-data and the enveloped-data content types are
   used.

   Since many of the Suite B algorithms enjoy uses in other environments
   as well, the majority of the conventions needed for the Suite B
   algorithms are already specified in other documents.  This document
   references the source of these conventions, and the relevant details
   are repeated to aid developers that choose to support Suite B.  In a
   few cases, additional algorithm identifiers are needed, and they are
   provided in this document.

1.1.  Terminology

   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].

1.2.  ASN.1

   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].

1.3.  Suite B Security Levels

   Suite B offers two security levels:  Level 1 and Level 2.  Security
   Level 2 offers greater cryptographic strength by using longer keys.

   For S/MIME signed messages, Suite B follows the direction set by RFC
   3278 [CMSECC], but some additional algorithm identifiers are
   assigned.  Suite B uses these algorithms:

                            Security Level 1   Security Level 2
                            ----------------   ----------------
      Message Digest:       SHA-256            SHA-384
      Signature:            ECDSA with P-256   ECDSA with P-384









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   For S/MIME encrypted messages, Suite B follows the direction set by
   RFC 3278 [CMSECC] and follows the conventions set by RFC 3565
   [CMSAES].  Again, additional algorithm identifiers are assigned.
   Suite B uses these algorithms:

                            Security Level 1   Security Level 2
                            ----------------   ----------------
      Key Agreement:        ECDH with P-256    ECDH with P-384
      Key Derivation:       SHA-256            SHA-384
      Key Wrap:             AES-128 Key Wrap   AES-256 Key Wrap
      Content Encryption:   AES-128 CBC        AES-256 CBC

2.  SHA-256 and SHA-256 Message Digest Algorithms

   This section specifies the conventions employed by implementations
   that support SHA-256 or SHA-384 [SHA2].  In Suite B Security Level 1,
   the SHA-256 message digest algorithm MUST be used.  In Suite B
   Security Level 2, SHA-384 MUST be used.

   Within the CMS signed-data content type, message digest algorithm
   identifiers are located in the SignedData digestAlgorithms field and
   the SignerInfo digestAlgorithm field.  Also, message digest values
   are located in the Message Digest authenticated attribute.  In
   addition, message digest values are input to signature algorithms.

   The SHA-256 and SHA-384 message digest algorithms are defined in FIPS
   Pub 180-2 [SHA2, EH].  The algorithm identifier for SHA-256 is:

      id-sha256  OBJECT IDENTIFIER  ::=  { joint-iso-itu-t(2)
          country(16) us(840) organization(1) gov(101) csor(3)
          nistalgorithm(4) hashalgs(2) 1 }

   The algorithm identifier for SHA-384 is:

      id-sha384  OBJECT IDENTIFIER  ::=  { joint-iso-itu-t(2)
          country(16) us(840) organization(1) gov(101) csor(3)
          nistalgorithm(4) hashalgs(2) 2 }

   There are two possible encodings for the AlgorithmIdentifier
   parameters field.  The two alternatives arise from the fact that when
   the 1988 syntax for AlgorithmIdentifier was translated into the 1997
   syntax the OPTIONAL associated with the AlgorithmIdentifier
   parameters got lost.  Later the OPTIONAL was recovered via a defect
   report, but by then many people thought that algorithm parameters
   were mandatory.  Because of this history some implementations encode
   parameters as a NULL element and others omit them entirely.  The
   correct encoding for the SHA-256 and SHA-384 message digest
   algorithms is to omit the parameters field; however, to ensure



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   compatibility, implementations ought to also handle a SHA-256 and
   SHA-384 AlgorithmIdentifier parameters field which contains a NULL.

   For both SHA-256 and SHA-384, the AlgorithmIdentifier parameters
   field is OPTIONAL, and if present, the parameters field MUST contain
   a NULL.  Implementations MUST accept SHA-256 and SHA-384
   AlgorithmIdentifiers with absent parameters.  Implementations MUST
   accept SHA-256 and SHA-384 AlgorithmIdentifiers with NULL parameters.
   Implementations SHOULD generate SHA-256 and SHA-384
   AlgorithmIdentifiers with absent parameters.

3.  ECDSA Signature Algorithm

   This section specifies the conventions employed by implementations
   that support ECDSA.  The direction set by RFC 3278 [CMSECC] is
   followed, but additional message digest algorithms and additional
   elliptic curves are employed.  In Suite B Security Level 1, ECDSA
   MUST be used with the SHA-256 message digest algorithm and the P-256
   elliptic curve.  In Suite B Security Level 2, ECDSA MUST be used with
   the SHA-384 message digest algorithm and the P-384 elliptic curve.
   The P-256 and P-384 elliptic curves are specified in [DSS].

   Within the CMS signed-data content type, signature algorithm
   identifiers are located in the SignerInfo signatureAlgorithm field of
   SignedData.  In addition, signature algorithm identifiers are located
   in the SignerInfo signatureAlgorithm field of countersignature
   attributes.

   Within the CMS signed-data content type, signature values are located
   in the SignerInfo signature field of SignedData.  In addition,
   signature values are located in the SignerInfo signature field of
   countersignature attributes.

   As specified in RFC 3279 [PKIX1ALG], ECDSA and ECDH use the same
   algorithm identifier for subject public keys in certificates, and it
   is repeated here:

      id-ecPublicKey  OBJECT IDENTIFIER  ::=  { iso(1) member-body(2)
          us(840) ansi-x9-62(10045) keyType(2) 1 }

   This object identifier is used in public key certificates for both
   ECDSA signature keys and ECDH encryption keys.  The intended
   application for the key may be indicated in the key usage field (see
   RFC 3280 [PKIX1]).  The use of separate keys for signature and
   encryption purposes is RECOMMENDED; however, the use of a single key
   for both signature and encryption purposes is not forbidden.

   As specified in RFC 3279 [PKIX1ALG], ECDSA and ECDH use the same



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   encoding for subject public keys in certificates, and it is repeated
   here:

      ECPoint  ::=  OCTET STRING

   The elliptic curve public key (an OCTET STRING) is mapped to a
   subject public key (a BIT STRING) as follows:  the most significant
   bit of the OCTET STRING becomes the most significant bit of the BIT
   STRING, and the least significant bit of the OCTET STRING  becomes
   the least significant bit of the BIT STRING.  Note that this octet
   string may represent an elliptic curve point in compressed or
   uncompressed form.  Implementations that support elliptic curves
   according to this specification MUST support the uncompressed form
   and MAY support the compressed form.

   ECDSA and ECDH require use of certain parameters with the public key.
   The parameters may be inherited from the certificate issuer,
   implicitly included through reference to a named curve, or explicitly
   included in the certificate.  As specified in RFC 3279 [PKIX1ALG],
   the parameter structure is:

      EcpkParameters  ::=  CHOICE {
        ecParameters  ECParameters,
        namedCurve    OBJECT IDENTIFIER,
        implicitlyCA  NULL }

   In Suite B, the namedCurve CHOICE MUST be used.  The object
   identifier for P-256 is:

      ansip256r1  OBJECT IDENTIFIER  ::=  { iso(1) member-body(2)
          us(840) ansi-x9-62(10045) curves(3) prime(1) 7 }

   The object identifier for P-384 is:

      secp384r1  OBJECT IDENTIFIER  ::=  { iso(1)
          identified-organization(3) certicom(132) curve(0) 34 }

   The algorithm identifier used in CMS for ECDSA with SHA-256 signature
   values is:

      ecdsa-with-SHA256  OBJECT IDENTIFIER  ::=  { iso(1) member-body(2)
          us(840) ansi-X9-62(10045) signatures(4) ecdsa-with-sha2(3) 2 }

   The algorithm identifier used in CMS for ECDSA with SHA-384 signature
   values is:

      ecdsa-with-SHA384  OBJECT IDENTIFIER  ::=  { iso(1) member-body(2)
          us(840) ansi-X9-62(10045) signatures(4) ecdsa-with-sha2(3) 3 }



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   When either the ecdsa-with-SHA256 or the ecdsa-with-SHA384 algorithm
   identifier is used, the AlgorithmIdentifier parameters field MUST be
   absent.

   When signing, the ECDSA algorithm generates two values, commonly
   called r and s.  To transfer these two values as one signature, they
   MUST be encoded using the Ecdsa-Sig-Value type specified in RFC 3279
   [PKIX1ALG]:

      Ecdsa-Sig-Value  ::=  SEQUENCE {
        r  INTEGER,
        s  INTEGER }

4.  Key Management

   CMS accommodates the following general key management techniques: key
   agreement, key transport, previously distributed symmetric key-
   encryption keys, and passwords.  In Suite B, ephemeral-static key
   agreement MUST be used as described in Section 4.1.

   When a key agreement algorithm is used, a key-encryption algorithm is
   also needed.  In Suite B, the AES key Wrap as specified in RFC 3394
   [AESWRAP, SH] MUST be used as the key-encryption algorithm.  AES Key
   Wrap is discussed further in Section 4.2.  The key-encryption key
   used with the AES Key Wrap algorithm is obtained from a key
   derivation function (KDF).  In Suite B, there are two KDFs, one based
   on SHA-256 and one based on SHA-384.  These KDFs are discussed
   further in Section 4.3.

4.1.  ECDH Key Agreement Algorithm

   This section specifies the conventions employed by implementations
   that support ECDH.  The direction set by RFC 3278 [CMSECC] is
   followed, but additional key derivation functions and key wrap
   algorithms are employed.  S/MIME is used in store-and-forward
   communications, which means that ephemeral-static ECDH is always
   employed.  This means that the message originator uses an ephemeral
   ECDH key and that the message recipient uses a static ECDH key, which
   is obtained from an X.509 certificate.  In Suite B Security Level 1,
   ephemeral-static ECDH MUST be used with the SHA-256 KDF, AES-128 key
   wrap, and the P-256 elliptic curve.  In Suite B Security Level 2,
   ephemeral-static ECDH MUST be used with the SHA-384 KDF, AES-256 key
   wrap, and the P-384 elliptic curve.

   Within the CMS enveloped-data content type, key agreement algorithm
   identifiers are located in the EnvelopedData RecipientInfos
   KeyAgreeRecipientInfo keyEncryptionAlgorithm field.




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   As specified in RFC 3279 [PKIX1ALG], ECDSA and ECDH use the same
   conventions for carrying a subject public key in a certificate.
   These conventions are discussed in Section 3.

   Ephemeral-static ECDH key agreement is defined in [SEC1] and
   [IEEE1363].  When using ephemeral-static ECDH, the EnvelopedData
   RecipientInfos keyAgreeRecipientInfo field is used as follows:

      version MUST be 3.

      originator MUST be the originatorKey alternative.  The
      originatorKey algorithm field MUST contain the id-ecPublicKey
      object identifier (see Section 3) with NULL parameters.  The
      originatorKey publicKey field MUST contain the message
      originator's ephemeral public key, which is a DER-encoded ECPoint
      (see Section 3).  The ECPoint SHOULD be represented in
      uncompressed form.

      ukm can be present or absent.  However, message originators SHOULD
      include the ukm.  As specified in RFC 3852 [CMS], implementations
      MUST support ukm message recipient processing, so interoperability
      is not a concern if the ukm is present or absent.  When present,
      the ukm is used to ensure that a different key-encryption key is
      generated, even when the ephemeral private key is improperly used
      more than once.  See [RANDOM] for guidance on generation of random
      values.

      keyEncryptionAlgorithm MUST be one of the two algorithm
      identifiers listed below, and the algorithm identifier parameter
      field MUST be present and identify the key wrap algorithm.  The
      key wrap algorithm denotes the symmetric encryption algorithm used
      to encrypt the content-encryption key with the pairwise key-
      encryption key generated using the ephemeral-static ECDH key
      agreement algorithm (see Section 4.3).  In Suite B Security Level
      1, the keyEncryptionAlgorithm MUST be dhSinglePass-stdDH-
      sha256kdf-scheme, and the keyEncryptionAlgorithm parameter MUST be
      a KeyWrapAlgorithm containing id-aes128-wrap (see Section 4.2).
      In Suite B Security Level 2, the keyEncryptionAlgorithm MUST be
      dhSinglePass-stdDH-sha384kdf-scheme, and the
      keyEncryptionAlgorithm parameter MUST be a KeyWrapAlgorithm
      containing id-aes256-wrap (see Section 4.2).  The algorithm
      identifier for dhSinglePass-stdDH-sha256kdf-scheme and









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      dhSinglePass-stdDH-sha384kdf-scheme are:

         dhSinglePass-stdDH-sha256kdf-scheme  OBJECT IDENTIFIER  ::=
             { iso(1) identified-organization(3) certicom(132)
               schemes(1) 11 1 }

         dhSinglePass-stdDH-sha384kdf-scheme  OBJECT IDENTIFIER  ::=
             { iso(1) identified-organization(3) certicom(132)
               schemes(1) 11 2 }

      Both of these algorithm identifiers use KeyWrapAlgorithm as the
      type for their parameter:

         KeyWrapAlgorithm  ::=  AlgorithmIdentifier

      recipientEncryptedKeys contains an identifier and an encrypted key
      for each recipient.  The RecipientEncryptedKey
      KeyAgreeRecipientIdentifier MUST contain either the
      issuerAndSerialNumber identifying the recipient's certificate or
      the RecipientKeyIdentifier containing the subject key identifier
      from the recipient's certificate.  In both cases, the recipient's
      certificate contains the recipient's static ECDH public key.
      RecipientEncryptedKey EncryptedKey MUST contain the content-
      encryption key encrypted with the ephemeral-static ECDH generated
      pairwise key-encryption key using the algorithm specified by the
      KeyWrapAlgorithm (see section 4.3).

4.2.  AES Key Wrap

   CMS offers support for symmetric key-encryption key management;
   however, it is not used in Suite B.  Rather, the AES Key Wrap key-
   encryption algorithm, as specified in RFC 3394 [AESWRAP, SH], is used
   to encrypt the content-encryption key with a pairwise key-encryption
   key that is generated using ephemeral-static ECDH.  In Suite B
   Security Level 1, AES-128 Key Wrap MUST be used as the key-encryption
   algorithm.  In Suite B Security Level 2, AES-256 Key Wrap MUST be
   used as the key-encryption algorithm.

   Within the CMS enveloped-data content type, wrapped content-
   encryption keys are located in the EnvelopedData RecipientInfos
   KeyAgreeRecipientInfo RecipientEncryptedKeys encryptedKey field, and
   key wrap algorithm identifiers are located in the KeyWrapAlgorithm
   parameters within the EnvelopedData RecipientInfos
   KeyAgreeRecipientInfo keyEncryptionAlgorithm field.







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   The algorithm identifiers for AES Key Wrap are specified in RFC 3394
   [SH], and the ones needed for Suite B are repeated here:

      id-aes128-wrap  OBJECT IDENTIFIER  ::=  { joint-iso-itu-t(2)
          country(16) us(840) organization(1) gov(101) csor(3)
          nistAlgorithm(4) aes(1) 5 }

      id-aes256-wrap  OBJECT IDENTIFIER  ::=  { joint-iso-itu-t(2)
          country(16) us(840) organization(1) gov(101) csor(3)
          nistAlgorithm(4) aes(1) 45 }

4.3.  Key Derivation Functions

   CMS offers support for deriving symmetric key-encryption keys from
   passwords; however, password-based key management is not used in
   Suite B.  Rather, KDFs based on SHA-256 and SHA-384 are used to
   derive a pairwise key-encryption key from the shared secret produced
   by ephemeral-static ECDH.  In Suite B Security Level 1, the KDF based
   on SHA-256 MUST be used.  In Suite B Security Level 2, KDF based on
   SHA-384 MUST be used.

   As specified in Section 8.2 of RFC 3278 [CMSECC], using ECDH with the
   CMS enveloped-data content type, the derivation of key-encryption
   keys makes use of the ECC-CMS-SharedInfo type, which is repeated
   here:

      ECC-CMS-SharedInfo  ::=  SEQUENCE {
        keyInfo      AlgorithmIdentifier,
        entityUInfo  [0] EXPLICIT OCTET STRING OPTIONAL,
        suppPubInfo  [2] EXPLICIT OCTET STRING }

   In Suite B, the fields of ECC-CMS-SharedInfo are used as follows:

      keyInfo contains the object identifier of the key-encryption
      algorithm that will be used to wrap the content-encryption key and
      NULL parameters.  In Suite B Security Level 1, AES-128 Key Wrap
      MUST be used, resulting in {id-aes128-wrap, NULL}.  In Suite B
      Security Level 2, AES-256 Key Wrap MUST be used, resulting in
      {id-aes256-wrap, NULL}.

      entityUInfo optionally contains a random value provided by the
      message originator.  If the ukm is present, then the entityUInfo
      MUST be present, and it MUST contain the ukm value.  If the ukm is
      not present, then the entityUInfo MUST be absent.







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      suppPubInfo contains the length of the generated key-encryption
      key, in bits, represented as a 32 bit unsigned number, as
      described in RFC 2631 [CMSDH].  In Suite B Security Level 1, a
      128-bit AES key MUST be used, resulting in 0x00000080.  In Suite B
      Security Level 2, a 256-bit AES key MUST be used, resulting in
      0x00000100.

   ECC-CMS-SharedInfo is DER-encoded and used as input to the key
   derivation function, as specified in Section 3.6.1 of [SEC1].  Note
   that ECC-CMS-SharedInfo differs from the OtherInfo specified in
   [CMSDH].  Here, a counter value is not included in the keyInfo field
   because the KDF specified in [SEC1] ensures that sufficient keying
   data is provided.

   The KDF specified in [SEC1] provides an algorithm for generating an
   essentially arbitrary amount of keying material from the shared
   secret produced by ephemeral-static ECDH, which is called Z for the
   remainder of this discussion.  The KDF can be summarized as:

      KM = Hash ( Z || Counter || ECC-CMS-SharedInfo )

   To generate a key-encryption key, one or more KM blocks are
   generated, incrementing Counter appropriately, until enough material
   has been generated.  The KM blocks are concatenated left to right:

      KEK = KM ( counter=1 ) || KM ( counter=2 ) ...

   The elements of the KDF are used as follows:

      Hash is the one-way hash function, and it is either SHA-256 or
      SHA-384 [SHA2].  In Suite B Security Level 1, the SHA-256 MUST be
      used.  In Suite B Security Level 2, SHA-384 MUST be used.

      Z is the shared secret value generated by ephemeral-static ECDH.
      Leading zero bits MUST be preserved.  In Suite B Security Level 1,
      Z MUST be exactly 256 bits.  In Suite B Security Level 2, Z MUST
      be exactly 384 bits.

      Counter is a 32 bit unsigned number, represented in network byte
      order.  Its initial value MUST be 0x00000001 for any key
      derivation operation.  In Suite B Security Level 1 and Security
      Level 2, exactly one iteration is needed; the Counter is not
      incremented.

      ECC-CMS-SharedInfo is composed as described above.  It MUST be DER
      encoded.





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   To generate a key-encryption key, one KM block is generated, with a
   Counter value of 0x00000001:

      KEK = KM ( 1 ) = Hash ( Z || Counter=1 || ECC-CMS-SharedInfo )

   In Suite B Security Level 1, the key-encryption key MUST be the most
   significant 128 bits of the SHA-256 output value.  In Suite B
   Security Level 2, the key-encryption key MUST be the most significant
   256 bits of the SHA-384 output value.

   Note that the only source of secret entropy in this computation is Z.
   The effective key space of the key-encryption key is limited by the
   size of Z, in addition to any security level considerations imposed
   by the elliptic curve that is used.  However, if entityUInfo is
   different for each message, a different key-encryption key will be
   generated for each message.

5.  AES CBC Content Encryption

   This section specifies the conventions employed by implementations
   that support content encryption using AES [AES] in Cipher Block
   Chaining (CBC) mode [MODES].  The conventions in RFC 3565 [CMSAES]
   are followed.  In Suite B Security Level 1, the AES-128 in CBC mode
   MUST be used for content encryption.  In Suite B Security Level 2,
   AES-256 in CBC mode MUST be used.

   Within the CMS enveloped-data content type, content encryption
   algorithm identifiers are located in the EnvelopedData
   EncryptedContentInfo contentEncryptionAlgorithm field.  The content
   encryption algorithm is used to encipher the content located in the
   EnvelopedData EncryptedContentInfo encryptedContent field.

   The AES CBC content-encryption algorithm is described in [AES] and
   [MODES].  The algorithm identifier for AES-128 in CBC mode is:

      id-aes128-CBC  OBJECT IDENTIFIER  ::=  { joint-iso-itu-t(2)
          country(16) us(840) organization(1) gov(101) csor(3)
          nistAlgorithm(4) aes(1) 2 }

   The algorithm identifier for AES-256 in CBC mode is:

      id-aes256-CBC  OBJECT IDENTIFIER  ::=  { joint-iso-itu-t(2)
          country(16) us(840) organization(1) gov(101) csor(3)
          nistAlgorithm(4) aes(1) 42 }







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   The AlgorithmIdentifier parameters field MUST be present, and the
   parameters field must contain AES-IV:

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

   The 16 octet initialization vector is generated at random by the
   originator.  See [RANDOM] for guidance on generation of random
   values.

6.  Security Considerations

   This document specifies the conventions for using the NSA's Suite B
   algorithms in S/MIME.  All of the algorithms have been specified in
   previous documents, although a few new algorithm identifiers have
   been assigned.

   Two levels of security may be achieved using this specification.
   Users must consider their risk environment to determine which level
   is appropriate for their own use.

   For signed and encrypted messages, Suite B provides a consistent
   level of security for confidentiality and integrity of the message
   content.

   The security considerations in RFC 3852 [CMS] discuss the CMS as a
   method for digitally signing data and encrypting data.

   The security considerations in RFC 3370 [CMSALG] discuss
   cryptographic algorithm implementation concerns in the context of the
   CMS.

   The security considerations in RFC 3278 [CMSECC] discuss the use of
   elliptic curve cryptography (ECC) in the CMS.

   The security considerations in RFC 3565 [CMSAES] discuss the use of
   AES in the CMS.

7.  References

7.1.  Normative References

   [AES]       National Institute of Standards and Technology, "Advanced
               Encryption Standard (AES)", FIPS PUB 197, November 2001.

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




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   [DSS]       National Institute of Standards and Technology, "Digital
               Signature Standard (DSS)", FIPS PUB 186-2, January 2000.

   [ECDSA]     American National Standards Institute, "Public Key
               Cryptography For The Financial Services Industry: The
               Elliptic Curve Digital Signature Algorithm (ECDSA)",
               ANSI X9.62-1998, 1999.

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

   [CMSAES]    Schaad, J., "Use of the Advanced Encryption Standard
               (AES) Encryption Algorithm in Cryptographic Message
               Syntax (CMS)", RFC 3565, July 2003.

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

   [CMSDH]     Rescorla, E., "Diffie-Hellman Key Agreement Method",
               RFC 2631, June 1999.

   [CMSECC]    Blake-Wilson, S., Brown, D., and P. Lambert, "Use of
               Elliptic Curve Cryptography (ECC) Algorithms in
               Cryptographic Message Syntax (CMS)", RFC 3278,
               April 2002.

   [IEEE1363]  Institute of Electrical and Electronics Engineers,
               "Standard Specifications for Public Key Cryptography",
               IEEE Std 1363, 2000.

   [MODES]     National Institute of Standards and Technology, "DES
               Modes of Operation", FIPS Pub 81, 2 December 1980.

   [MSG]       Ramsdell, B., "Secure/Multipurpose Internet Mail
               Extensions (S/MIME) Version 3.1 Message Specification",
               RFC 3851, July 2004.

   [PKIX1]     Housley, R., Polk, W., Ford, W. and D. Solo, "Internet
               X.509 Public Key Infrastructure Certificate and
               Certificate Revocation List (CRL) Profile", RFC 3280,
               April 2002.

   [PKIX1ALG]  Polk, W., Housley, R., and L. Bassham, "Algorithms and
               Identifiers for the Internet X.509 Public Key
               Infrastructure Certificate and Certificate Revocation
               List (CRL) Profile", RFC 3279, April 2002.





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   [SEC1]      Standards for Efficient Cryptography Group, "Elliptic
               Curve Cryptography", 2000.  [See http://www.secg.org/
               collateral/sec1.pdf.]

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

   [SHA2]      National Institute of Standards and Technology, "Secure
               Hash Standard", FIPS 180-2, 1 August 2002.

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

   [X.208-88]   CCITT.  Recommendation X.208: Specification of Abstract
                Syntax Notation One (ASN.1).  1988.

   [X.209-88]   CCITT.  Recommendation X.209: Specification of Basic
                Encoding Rules for Abstract Syntax Notation One (ASN.1).
                1988.

   [X.509-88]   CCITT.  Recommendation X.509: The Directory -
                Authentication Framework.  1988.

7.2.  Informative References

   [EH]        Eastlake, D., and T. Hansen, "US Secure Hash Algorithms
               (SHA and HMAC-SHA)", RFC 4634, July 2006.

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

   [SuiteB]    National Security Agency, "Fact Sheet NSA Suite B
               Cryptography", July 2005.  [See http://www.nsa.gov/ia/
               industry/crypto_Suite_b.cfm?MenuID=10.2.7)

8.  IANA Considerations

   None.

   {{{ RFC Editor: Please remove this section prior to publication. }}}











Housley                                                        [Page 14]

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Authors' Addresses

   Russell Housley
   Vigil Security, LLC
   918 Spring Knoll Drive
   Herndon, VA 20170
   USA

   EMail: housley(at)vigilsec.com

   Jerome A. Solinas
   National Information Assurance Laboratory
   National Security Agency
   9800 Savage Road
   Fort George G. Meade, MD  20755
   USA

   Email: jasolin(at)orion.ncsc.mil

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Housley                                                        [Page 15]

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Housley                                                        [Page 16]


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