Suite B in Secure/Multipurpose Internet Mail Extensions (S/MIME)
RFC 6318

Internet Engineering Task Force (IETF)                        R. Housley
Request for Comments: 6318                                Vigil Security
Obsoletes: 5008                                               J. Solinas
Category: Informational                         National Security Agency
ISSN: 2070-1721                                                June 2011

    Suite B in Secure/Multipurpose Internet Mail Extensions (S/MIME)

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 5751.  This
   document obsoletes RFC 5008.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Not all documents
   approved by the IESG are a candidate for any level of Internet
   Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc6318.

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Copyright Notice

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   document authors.  All rights reserved.

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Table of Contents

   1. Introduction ....................................................3
      1.1. Terminology ................................................4
      1.2. ASN.1 ......................................................4
      1.3. Suite B Security Levels ....................................4
   2. SHA-256 and SHA-384 Message Digest Algorithms ...................5
   3. ECDSA Signature Algorithm .......................................6
   4. Key Management ..................................................7
      4.1. ECDH Key Agreement Algorithm ...............................7
      4.2. AES Key Wrap ...............................................8
      4.3. Key Derivation Functions ...................................9
   5. AES CBC Content Encryption .....................................11
   6. Security Considerations ........................................12
   7. References .....................................................13
      7.1. Normative References ......................................13
      7.2. Informative References ....................................14

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1.  Introduction

   The Fact Sheet on National Security Agency (NSA) Suite B Cryptography
   [NSA] states:

      A Cryptographic Interoperability Strategy (CIS) was developed to
      find ways to increase assured rapid sharing of information both
      within the U.S. and between the U.S. and her partners through the
      use of a common suite of public standards, protocols, algorithms
      and modes referred to as the "Secure Sharing Suite" or S.3.  The
      implementation of CIS will facilitate the development of a broader
      range of secure cryptographic products which will be available to
      a wide customer base.  The use of selected public cryptographic
      standards and protocols and Suite B is the core of CIS.

      In 2005, NSA announced Suite B Cryptography which built upon the
      National Policy on the use of the Advanced Encryption Standard
      (AES) to Protect National Security Systems and National Security
      Information.  In addition to the AES algorithm, Suite B includes
      cryptographic algorithms for key exchanges, digital signatures and
      hashing.  Suite B cryptography has been selected from cryptography
      that has been approved by NIST for use by the U.S. Government and
      specified in NIST standards or recommendations.

   This document specifies the conventions for using the United States
   National Security Agency's Suite B algorithms [NSA] 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.  This document only addresses Suite B compliance for S/MIME.
   Other applications of CMS are outside the scope of this document.

   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, with some relevant
   details repeated to aid developers that choose to support Suite B.

   This specification obsoletes RFC 5008 [SUITEBSMIME].  The primary
   reason for the publication of this document is to allow greater
   flexibility in the use of the Suite B Security Levels as discussed in
   Section 1.3.  It also removes some duplication between this document
   and referenced RFCs.

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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], 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 suites of algorithms for key agreement, key
   derivation, key wrap and content encryption, and two possible
   combinations of hash and signing algorithm.  Suite B algorithms are
   defined to support two minimum levels of cryptographic security: 128
   and 192 bits.

   For S/MIME signed messages, Suite B follows the direction set by
   RFC 5753 [CMSECC] and RFC 5754 [SHA2].  Suite B uses these
   combinations of message digest (hash) and signature functions (Sig
   Sets):

                            Sig Set 1          Sig Set 2
                            ----------------   ----------------
      Message Digest:       SHA-256            SHA-384
      Signature:            ECDSA with P-256   ECDSA with P-384

   For S/MIME encrypted messages, Suite B follows the direction set by
   RFC 5753 [CMSECC] and follows the conventions set by RFC 3565
   [CMSAES].

   Suite B uses these key establishment (KE) algorithms (KE Sets):

                            KE Set 1           KE Set 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

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   The two elliptic curves used in Suite B are specified in [DSS], and
   each appear in the literature under two different names.  For the
   sake of clarity, we list both names below:

      Curve       NIST Name    SECG Name    OID  [DSS]
      ---------------------------------------------------------
      nistp256    P-256        secp256r1    1.2.840.10045.3.1.7
      nistp384    P-384        secp384r1    1.3.132.0.34

   If configured at a minimum level of security of 128 bits, a Suite B
   compliant S/MIME system performing encryption MUST use either KE
   Set 1 or KE Set 2, with KE Set 1 being the preferred suite.  A
   digital signature, if applied, MUST use either Sig Set 1 or Sig Set
   2, independent of the encryption choice.

   A recipient in an S/MIME system configured at a minimum level of
   security of 128 bits MUST be able to verify digital signatures from
   Sig Set 1 and SHOULD be able to verify digital signatures from Sig
   Set 2.

   Note that for S/MIME systems configured at a minimum level of
   security of 128 bits, the algorithm set used for a signed-data
   content type is independent of the algorithm set used for an
   enveloped-data content type.

   If configured at a minimum level of security of 192 bits, a Suite B
   compliant S/MIME system performing encryption MUST use KE Set 2.  A
   digital signature, if applied, MUST use Sig Set 2.

   A recipient in an S/MIME system configured at a minimum level of
   security of 192 bits MUST be able to verify digital signatures from
   Sig Set 2.

2.  SHA-256 and SHA-384 Message Digest Algorithms

   SHA-256 and SHA-384 are the Suite B message digest algorithms.
   RFC 5754 [SHA2] specifies the conventions for using SHA-256 and
   SHA-384 with the Cryptographic Message Syntax (CMS).  Suite B
   compliant S/MIME implementations MUST follow the conventions in
   RFC 5754.  Relevant details are repeated below.

   Within the CMS signed-data content type, message digest algorithm
   identifiers are located in the SignedData digestAlgorithms field and
   the SignerInfo digestAlgorithm field.

   The SHA-256 and SHA-384 message digest algorithms are defined in FIPS
   Pub 180-3 [SHA2FIPS].  The algorithm identifiers for SHA-256 and
   SHA-384 are defined in [SHA2] and are repeated here:

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

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

   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.
   As specified in RFC 5754 [SHA2], implementations MUST generate
   SHA-256 and SHA-384 AlgorithmIdentifiers with absent parameters.

3.  ECDSA Signature Algorithm

   In Suite B, public key certificates used to verify S/MIME signatures
   MUST be compliant with the Suite B Certificate Profile specified in
   RFC 5759 [SUITEBCERT].

   The Elliptic Curve Digital Signature Algorithm (ECDSA) is the Suite B
   digital signature algorithm.  RFC 5753 [CMSECC] specifies the
   conventions for using ECDSA with the Cryptographic Message Syntax
   (CMS).  Suite B compliant S/MIME implementations MUST follow the
   conventions in RFC 5753.  Relevant details are repeated below.

   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.

   RFC 5480 [PKI-ALG] defines the signature algorithm identifiers used
   in CMS for ECDSA with SHA-256 and ECDSA with SHA-384.  The
   identifiers are repeated here:

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

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

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

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   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 5480
   [PKI-ALG]:

      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 for S/MIME, 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 for S/MIME, the Advanced Encryption Standard
   (AES) Key Wrap, as specified in RFC 3394 [SH] and [AESWRAP], 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 for S/MIME, 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

   Elliptic Curve Diffie-Hellman (ECDH) is the Suite B key agreement
   algorithm.

   S/MIME is used in store-and-forward communications, which means that
   ephemeral-static ECDH is always employed.  This means that the
   message originator possesses an ephemeral ECDH key pair and that the
   message recipient possesses a static ECDH key pair whose public key
   is represented by an X.509 certificate.  In Suite B, the certificate
   used to obtain the recipient's public key MUST be compliant with the
   Suite B Certificate Profile specified in RFC 5759 [SUITEBCERT].

   Section 3.1 of RFC 5753 [CMSECC] specifies the conventions for using
   ECDH with the CMS.  Suite B compliant S/MIME implementations MUST
   follow these conventions.  Relevant details are repeated below.

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

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   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).

   When implementing KE Set 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).  When implementing KE Set 2, the keyEncryptionAlgorithm
   MUST be dhSinglePass-stdDH-sha384kdf-scheme, and the
   keyEncryptionAlgorithm parameter MUST be a KeyWrapAlgorithm
   containing id-aes256-wrap.

   The algorithm identifiers for dhSinglePass-stdDH-sha256kdf-scheme and
   dhSinglePass-stdDH-sha384kdf-scheme, repeated from Section 7.1.4 of
   [CMSECC], 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

4.2.  AES Key Wrap

   The AES Key Wrap key-encryption algorithm, as specified in RFC 3394
   [SH] and [AESWRAP], is used to encrypt the content-encryption key
   with a pairwise key-encryption key that is generated using ephemeral-
   static ECDH.  Section 8 of RFC 5753 [CMSECC] specifies the
   conventions for using AES Key Wrap with the pairwise key generated
   with ephemeral-static ECDH with the CMS.  Suite B compliant S/MIME
   implementations MUST follow these conventions.  Relevant details are
   repeated below.

   When implementing KE Set 1, the KeyWrapAlgorithm MUST be
   id-aes128-wrap.  When implementing KE Set 2, the KeyWrapAlgorithm
   MUST be id-aes256-wrap.

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

   The algorithm identifiers for AES Key Wrap are specified in RFC 3394
   [SH], and the ones needed for Suite B compliant S/MIME
   implementations 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

   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.  Sections 7.1.8 and 7.2 of RFC 5753 [CMSECC] specify the
   conventions for using the KDF with the shared secret generated with
   ephemeral-static ECDH with the CMS.  Suite B compliant S/MIME
   implementations MUST follow these conventions.  Relevant details are
   repeated below.

   When implementing KE Set 1, the KDF based on SHA-256 MUST be used.
   When implementing KE Set 2, the KDF based on SHA-384 MUST be used.

   As specified in Section 7.2 of RFC 5753 [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 }

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

      keyInfo contains the object identifier of the key-encryption
         algorithm used to wrap the content-encryption key.  In Suite B
         for S/MIME, if the AES-128 Key Wrap is used, then the keyInfo
         will contain id-aes128-wrap, and the parameters will be absent.
         In Suite B for S/MIME, if AES-256 Key Wrap is used, then the
         keyInfo will contain id-aes256-wrap, and the parameters will be
         absent.

      entityUInfo optionally contains a random value provided by the
         message originator.  If the user keying material (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.

      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].  When a 128-bit AES key is used,
         the length MUST be 0x00000080.  When a 256-bit AES key is used,
         the length MUST be 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 (KM) 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 (KEK), 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.  If KE Set 1 is used, the
         SHA-256 hash MUST be used.  If KE Set 2 is used, the SHA-384
         hash MUST be used.

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      Z is the shared secret value generated by ephemeral-static ECDH.
         Leading zero bits MUST be preserved.  In Suite B for S/MIME, if
         KE Set 1 is used, Z MUST be exactly 256 bits.  In Suite B for
         S/MIME, if KE Set 2 is used, 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 for S/MIME, with both KE
         Set 1 and KE Set 2, exactly one iteration is needed; the
         Counter is not incremented.

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

   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 for S/MIME, when KE Set 1 is used, the key-encryption key
   MUST be the most significant 128 bits of the SHA-256 output value.
   In Suite B for S/MIME, when KE Set 2 is used, 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

   AES [AES] in Cipher Block Chaining (CBC) mode [MODES] is the Suite B
   for S/MIME content-encryption algorithm.  RFC 3565 [CMSAES] specifies
   the conventions for using AES with the CMS.  Suite B compliant S/MIME
   implementations MUST follow these conventions.  Relevant details are
   repeated below.

   In Suite B for S/MIME, if KE Set 1 is used, AES-128 in CBC mode MUST
   be used for content encryption.  In Suite B for S/MIME, if KE Set 2
   is used, 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.

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   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 }

   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 and algorithm
   identifiers have been specified in previous documents.

   Two minimum 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.

   See [RANDOM] for guidance on generation of random values.

   The security considerations in RFC 5652 [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 5753 [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.

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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", November 2001.

   [DSS]       National Institute of Standards and Technology, "Digital
               Signature Standard (DSS)", FIPS PUB 186-3, June 2009.

   [CMS]       Housley, R., "Cryptographic Message Syntax (CMS)",
               STD 70, RFC 5652, September 2009.

   [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]    Turner, S. and D. Brown, "Use of Elliptic Curve
               Cryptography (ECC) Algorithms in Cryptographic Message
               Syntax (CMS)", RFC 5753, January 2010.

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

   [MSG]       Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet
               Mail Extensions (S/MIME) Version 3.2 Message
               Specification", RFC 5751, January 2010.

   [PKI-ALG]   Turner, S., Brown, D., Yiu, K., Housley, R., and T. Polk,
               "Elliptic Curve Cryptography Subject Public Key
               Information", RFC 5480, March 2009.

   [SEC1]      Standards for Efficient Cryptography Group, "SEC 1:
               Elliptic Curve Cryptography", September 2000.
               <http://www.secg.org/collateral/sec1_final.pdf>.

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

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   [SHA2]      Turner, S., "Using SHA2 Algorithms with Cryptographic
               Message Syntax", RFC 5754, January 2010.

   [SHA2FIPS]  National Institute of Standards and Technology, "Secure
               Hash Standard (SHS)", FIPS 180-3, October 2008.

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

   [SUITEBCERT]
               Solinas, J. and L. Zieglar, "Suite B Certificate and
               Certificate Revocation List (CRL) Profile", RFC 5759,
               January 2010.

   [SUITEBSMIME]
               Housley, R. and J. Solinas, "Suite B in
               Secure/Multipurpose Internet Mail Extensions (S/MIME)",
               RFC 5008, September 2007.

   [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

   [RANDOM]    Eastlake 3rd, D., Schiller, J., and S. Crocker,
               "Randomness Requirements for Security", BCP 106,
               RFC 4086, June 2005.

   [NSA]       U.S. National Security Agency, "Fact Sheet NSA Suite B
               Cryptography", January 2009.
               <http://www.nsa.gov/ia/programs/suiteb_cryptography>.

Housley & Solinas             Informational                    [Page 14]
RFC 6318                    Suite B in S/MIME                  June 2011

Authors' Addresses

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

   EMail: housley@vigilsec.com

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

   EMail: jasolin@orion.ncsc.mil

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