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RFC 5652

 
 
 

Cryptographic Message Syntax (CMS)

Part 3 of 3, p. 34 to 56
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10.  Useful Types

   This section is divided into two parts.  The first part defines
   algorithm identifiers, and the second part defines other useful
   types.

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10.1.  Algorithm Identifier Types

   All of the algorithm identifiers have the same type:
   AlgorithmIdentifier.  The definition of AlgorithmIdentifier is taken
   from X.509 [X.509-88].

   There are many alternatives for each algorithm type.

10.1.1.  DigestAlgorithmIdentifier

   The DigestAlgorithmIdentifier type identifies a message-digest
   algorithm.  Examples include SHA-1, MD2, and MD5.  A message-digest
   algorithm maps an octet string (the content) to another octet string
   (the message digest).

      DigestAlgorithmIdentifier ::= AlgorithmIdentifier

10.1.2.  SignatureAlgorithmIdentifier

   The SignatureAlgorithmIdentifier type identifies a signature
   algorithm, and it can also identify a message digest algorithm.
   Examples include RSA, DSA, DSA with SHA-1, ECDSA, and ECDSA with
   SHA-256.  A signature algorithm supports signature generation and
   verification operations.  The signature generation operation uses the
   message digest and the signer's private key to generate a signature
   value.  The signature verification operation uses the message digest
   and the signer's public key to determine whether or not a signature
   value is valid.  Context determines which operation is intended.

      SignatureAlgorithmIdentifier ::= AlgorithmIdentifier

10.1.3.  KeyEncryptionAlgorithmIdentifier

   The KeyEncryptionAlgorithmIdentifier type identifies a key-encryption
   algorithm used to encrypt a content-encryption key.  The encryption
   operation maps an octet string (the key) to another octet string (the
   encrypted key) under control of a key-encryption key.  The decryption
   operation is the inverse of the encryption operation.  Context
   determines which operation is intended.

   The details of encryption and decryption depend on the key management
   algorithm used.  Key transport, key agreement, previously distributed
   symmetric key-encrypting keys, and symmetric key-encrypting keys
   derived from passwords are supported.

      KeyEncryptionAlgorithmIdentifier ::= AlgorithmIdentifier

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10.1.4.  ContentEncryptionAlgorithmIdentifier

   The ContentEncryptionAlgorithmIdentifier type identifies a content-
   encryption algorithm.  Examples include Triple-DES and RC2.  A
   content-encryption algorithm supports encryption and decryption
   operations.  The encryption operation maps an octet string (the
   plaintext) to another octet string (the ciphertext) under control of
   a content-encryption key.  The decryption operation is the inverse of
   the encryption operation.  Context determines which operation is
   intended.

      ContentEncryptionAlgorithmIdentifier ::= AlgorithmIdentifier

10.1.5.  MessageAuthenticationCodeAlgorithm

   The MessageAuthenticationCodeAlgorithm type identifies a message
   authentication code (MAC) algorithm.  Examples include DES-MAC and
   HMAC-SHA-1.  A MAC algorithm supports generation and verification
   operations.  The MAC generation and verification operations use the
   same symmetric key.  Context determines which operation is intended.

      MessageAuthenticationCodeAlgorithm ::= AlgorithmIdentifier

10.1.6.  KeyDerivationAlgorithmIdentifier

   The KeyDerivationAlgorithmIdentifier type is specified in RFC 3211
   [PWRI].  The KeyDerivationAlgorithmIdentifier definition is repeated
   here for completeness.

   Key derivation algorithms convert a password or shared secret value
   into a key-encryption key.

      KeyDerivationAlgorithmIdentifier ::= AlgorithmIdentifier

10.2.  Other Useful Types

   This section defines types that are used other places in the
   document.  The types are not listed in any particular order.

10.2.1.  RevocationInfoChoices

   The RevocationInfoChoices type gives a set of revocation status
   information alternatives.  It is intended that the set contain
   information sufficient to determine whether the certificates and
   attribute certificates with which the set is associated are revoked.
   However, there MAY be more revocation status information than
   necessary or there MAY be less revocation status information than
   necessary.  X.509 Certificate revocation lists (CRLs) [X.509-97] are

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   the primary source of revocation status information, but any other
   revocation information format can be supported.  The
   OtherRevocationInfoFormat alternative is provided to support any
   other revocation information format without further modifications to
   the CMS.  For example, Online Certificate Status Protocol (OCSP)
   Responses [OCSP] can be supported using the
   OtherRevocationInfoFormat.

   The CertificateList may contain a CRL, an Authority Revocation List
   (ARL), a Delta CRL, or an Attribute Certificate Revocation List.  All
   of these lists share a common syntax.

   The CertificateList type gives a certificate revocation list (CRL).
   CRLs are specified in X.509 [X.509-97], and they are profiled for use
   in the Internet in RFC 5280 [PROFILE].

   The definition of CertificateList is taken from X.509.

      RevocationInfoChoices ::= SET OF RevocationInfoChoice

      RevocationInfoChoice ::= CHOICE {
        crl CertificateList,
        other [1] IMPLICIT OtherRevocationInfoFormat }

      OtherRevocationInfoFormat ::= SEQUENCE {
        otherRevInfoFormat OBJECT IDENTIFIER,
        otherRevInfo ANY DEFINED BY otherRevInfoFormat }

10.2.2.  CertificateChoices

   The CertificateChoices type gives either a PKCS #6 extended
   certificate [PKCS#6], an X.509 certificate, a version 1 X.509
   attribute certificate (ACv1) [X.509-97], a version 2 X.509 attribute
   certificate (ACv2) [X.509-00], or any other certificate format.  The
   PKCS #6 extended certificate is obsolete.  The PKCS #6 certificate is
   included for backward compatibility, and PKCS #6 certificates SHOULD
   NOT be used.  The ACv1 is also obsolete.  ACv1 is included for
   backward compatibility, and ACv1 SHOULD NOT be used.  The Internet
   profile of X.509 certificates is specified in the "Internet X.509
   Public Key Infrastructure: Certificate and CRL Profile" [PROFILE].
   The Internet profile of ACv2 is specified in the "An Internet
   Attribute Certificate Profile for Authorization" [ACPROFILE].  The
   OtherCertificateFormat alternative is provided to support any other
   certificate format without further modifications to the CMS.

   The definition of Certificate is taken from X.509.

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   The definitions of AttributeCertificate are taken from X.509-1997 and
   X.509-2000.  The definition from X.509-1997 is assigned to
   AttributeCertificateV1 (see Section 12.2), and the definition from
   X.509-2000 is assigned to AttributeCertificateV2.

      CertificateChoices ::= CHOICE {
       certificate Certificate,
       extendedCertificate [0] IMPLICIT ExtendedCertificate, -- Obsolete
       v1AttrCert [1] IMPLICIT AttributeCertificateV1,       -- Obsolete
       v2AttrCert [2] IMPLICIT AttributeCertificateV2,
       other [3] IMPLICIT OtherCertificateFormat }

      OtherCertificateFormat ::= SEQUENCE {
        otherCertFormat OBJECT IDENTIFIER,
        otherCert ANY DEFINED BY otherCertFormat }

10.2.3.  CertificateSet

   The CertificateSet type provides a set of certificates.  It is
   intended that the set be sufficient to contain certification paths
   from a recognized "root" or "top-level certification authority" to
   all of the sender certificates with which the set is associated.
   However, there may be more certificates than necessary, or there MAY
   be fewer than necessary.

   The precise meaning of a "certification path" is outside the scope of
   this document.  However, [PROFILE] provides a definition for X.509
   certificates.  Some applications may impose upper limits on the
   length of a certification path; others may enforce certain
   relationships between the subjects and issuers of certificates within
   a certification path.

      CertificateSet ::= SET OF CertificateChoices

10.2.4.  IssuerAndSerialNumber

   The IssuerAndSerialNumber type identifies a certificate, and thereby
   an entity and a public key, by the distinguished name of the
   certificate issuer and an issuer-specific certificate serial number.

   The definition of Name is taken from X.501 [X.501-88], and the
   definition of CertificateSerialNumber is taken from X.509 [X.509-97].

      IssuerAndSerialNumber ::= SEQUENCE {
        issuer Name,
        serialNumber CertificateSerialNumber }

      CertificateSerialNumber ::= INTEGER

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10.2.5.  CMSVersion

   The CMSVersion type gives a syntax version number, for compatibility
   with future revisions of this specification.

      CMSVersion ::= INTEGER
                     { v0(0), v1(1), v2(2), v3(3), v4(4), v5(5) }

10.2.6.  UserKeyingMaterial

   The UserKeyingMaterial type gives a syntax for user keying material
   (UKM).  Some key agreement algorithms require UKMs to ensure that a
   different key is generated each time the same two parties generate a
   pairwise key.  The sender provides a UKM for use with a specific key
   agreement algorithm.

      UserKeyingMaterial ::= OCTET STRING

10.2.7.  OtherKeyAttribute

   The OtherKeyAttribute type gives a syntax for the inclusion of other
   key attributes that permit the recipient to select the key used by
   the sender.  The attribute object identifier must be registered along
   with the syntax of the attribute itself.  Use of this structure
   should be avoided since it might impede interoperability.

      OtherKeyAttribute ::= SEQUENCE {
        keyAttrId OBJECT IDENTIFIER,
        keyAttr ANY DEFINED BY keyAttrId OPTIONAL }

11.  Useful Attributes

   This section defines attributes that may be used with signed-data,
   enveloped-data, encrypted-data, or authenticated-data.  The syntax of
   Attribute is compatible with X.501 [X.501-88] and RFC 5280 [PROFILE].
   Some of the attributes defined in this section were originally
   defined in PKCS #9 [PKCS#9]; others were originally defined in a
   previous version of this specification [CMS1].  The attributes are
   not listed in any particular order.

   Additional attributes are defined in many places, notably the S/MIME
   Version 3.1 Message Specification [MSG3.1] and the Enhanced Security
   Services for S/MIME [ESS], which also include recommendations on the
   placement of these attributes.

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11.1.  Content Type

   The content-type attribute type specifies the content type of the
   ContentInfo within signed-data or authenticated-data.  The content-
   type attribute type MUST be present whenever signed attributes are
   present in signed-data or authenticated attributes present in
   authenticated-data.  The content-type attribute value MUST match the
   encapContentInfo eContentType value in the signed-data or
   authenticated-data.

   The content-type attribute MUST be a signed attribute or an
   authenticated attribute; it MUST NOT be an unsigned attribute,
   unauthenticated attribute, or unprotected attribute.

   The following object identifier identifies the content-type
   attribute:

      id-contentType OBJECT IDENTIFIER ::= { iso(1) member-body(2)
          us(840) rsadsi(113549) pkcs(1) pkcs9(9) 3 }

   Content-type attribute values have ASN.1 type ContentType:

      ContentType ::= OBJECT IDENTIFIER

   Even though the syntax is defined as a SET OF AttributeValue, a
   content-type attribute MUST have a single attribute value; zero or
   multiple instances of AttributeValue are not permitted.

   The SignedAttributes and AuthAttributes syntaxes are each defined as
   a SET OF Attributes.  The SignedAttributes in a signerInfo MUST NOT
   include multiple instances of the content-type attribute.  Similarly,
   the AuthAttributes in an AuthenticatedData MUST NOT include multiple
   instances of the content-type attribute.

11.2.  Message Digest

   The message-digest attribute type specifies the message digest of the
   encapContentInfo eContent OCTET STRING being signed in signed-data
   (see Section 5.4) or authenticated in authenticated-data (see Section
   9.2).  For signed-data, the message digest is computed using the
   signer's message digest algorithm.  For authenticated-data, the
   message digest is computed using the originator's message digest
   algorithm.

   Within signed-data, the message-digest signed attribute type MUST be
   present when there are any signed attributes present.  Within
   authenticated-data, the message-digest authenticated attribute type
   MUST be present when there are any authenticated attributes present.

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   The message-digest attribute MUST be a signed attribute or an
   authenticated attribute; it MUST NOT be an unsigned attribute,
   unauthenticated attribute, or unprotected attribute.

   The following object identifier identifies the message-digest
   attribute:

      id-messageDigest OBJECT IDENTIFIER ::= { iso(1) member-body(2)
          us(840) rsadsi(113549) pkcs(1) pkcs9(9) 4 }

   Message-digest attribute values have ASN.1 type MessageDigest:

      MessageDigest ::= OCTET STRING

   A message-digest attribute MUST have a single attribute value, even
   though the syntax is defined as a SET OF AttributeValue.  There MUST
   NOT be zero or multiple instances of AttributeValue present.

   The SignedAttributes syntax and AuthAttributes syntax are each
   defined as a SET OF Attributes.  The SignedAttributes in a signerInfo
   MUST include only one instance of the message-digest attribute.
   Similarly, the AuthAttributes in an AuthenticatedData MUST include
   only one instance of the message-digest attribute.

11.3.  Signing Time

   The signing-time attribute type specifies the time at which the
   signer (purportedly) performed the signing process.  The signing-time
   attribute type is intended for use in signed-data.

   The signing-time attribute MUST be a signed attribute or an
   authenticated attribute; it MUST NOT be an unsigned attribute,
   unauthenticated attribute, or unprotected attribute.

   The following object identifier identifies the signing-time
   attribute:

      id-signingTime OBJECT IDENTIFIER ::= { iso(1) member-body(2)
          us(840) rsadsi(113549) pkcs(1) pkcs9(9) 5 }

   Signing-time attribute values have ASN.1 type SigningTime:

      SigningTime ::= Time

      Time ::= CHOICE {
        utcTime UTCTime,
        generalizedTime GeneralizedTime }

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   Note: The definition of Time matches the one specified in the 1997
   version of X.509 [X.509-97].

   Dates between 1 January 1950 and 31 December 2049 (inclusive) MUST be
   encoded as UTCTime.  Any dates with year values before 1950 or after
   2049 MUST be encoded as GeneralizedTime.

   UTCTime values MUST be expressed in Coordinated Universal Time
   (formerly known as Greenwich Mean Time (GMT) and Zulu clock time) and
   MUST include seconds (i.e., times are YYMMDDHHMMSSZ), even where the
   number of seconds is zero.  Midnight MUST be represented as
   "YYMMDD000000Z".  Century information is implicit, and the century
   MUST be determined as follows:

      Where YY is greater than or equal to 50, the year MUST be
      interpreted as 19YY; and

      Where YY is less than 50, the year MUST be interpreted as 20YY.

   GeneralizedTime values MUST be expressed in Coordinated Universal
   Time and MUST include seconds (i.e., times are YYYYMMDDHHMMSSZ), even
   where the number of seconds is zero.  GeneralizedTime values MUST NOT
   include fractional seconds.

   A signing-time attribute MUST have a single attribute value, even
   though the syntax is defined as a SET OF AttributeValue.  There MUST
   NOT be zero or multiple instances of AttributeValue present.

   The SignedAttributes syntax and the AuthAttributes syntax are each
   defined as a SET OF Attributes.  The SignedAttributes in a signerInfo
   MUST NOT include multiple instances of the signing-time attribute.
   Similarly, the AuthAttributes in an AuthenticatedData MUST NOT
   include multiple instances of the signing-time attribute.

   No requirement is imposed concerning the correctness of the signing
   time, and acceptance of a purported signing time is a matter of a
   recipient's discretion.  It is expected, however, that some signers,
   such as time-stamp servers, will be trusted implicitly.

11.4.  Countersignature

   The countersignature attribute type specifies one or more signatures
   on the contents octets of the signature OCTET STRING in a SignerInfo
   value of the signed-data.  That is, the message digest is computed
   over the octets comprising the value of the OCTET STRING, neither the
   tag nor length octets are included.  Thus, the countersignature
   attribute type countersigns (signs in serial) another signature.

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   The countersignature attribute MUST be an unsigned attribute; it MUST
   NOT be a signed attribute, an authenticated attribute, an
   unauthenticated attribute, or an unprotected attribute.

   The following object identifier identifies the countersignature
   attribute:

      id-countersignature OBJECT IDENTIFIER ::= { iso(1) member-body(2)
          us(840) rsadsi(113549) pkcs(1) pkcs9(9) 6 }

   Countersignature attribute values have ASN.1 type Countersignature:

      Countersignature ::= SignerInfo

   Countersignature values have the same meaning as SignerInfo values
   for ordinary signatures, except that:

   1.  The signedAttributes field MUST NOT contain a content-type
       attribute; there is no content type for countersignatures.

   2.  The signedAttributes field MUST contain a message-digest
       attribute if it contains any other attributes.

   3.  The input to the message-digesting process is the contents octets
       of the DER encoding of the signatureValue field of the SignerInfo
       value with which the attribute is associated.

   A countersignature attribute can have multiple attribute values.  The
   syntax is defined as a SET OF AttributeValue, and there MUST be one
   or more instances of AttributeValue present.

   The UnsignedAttributes syntax is defined as a SET OF Attributes.  The
   UnsignedAttributes in a signerInfo may include multiple instances of
   the countersignature attribute.

   A countersignature, since it has type SignerInfo, can itself contain
   a countersignature attribute.  Thus, it is possible to construct an
   arbitrarily long series of countersignatures.

12.  ASN.1 Modules

   Section 12.1 contains the ASN.1 module for the CMS, and Section 12.2
   contains the ASN.1 module for the Version 1 Attribute Certificate.

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12.1.  CMS ASN.1 Module

   CryptographicMessageSyntax2004
     { iso(1) member-body(2) us(840) rsadsi(113549)
       pkcs(1) pkcs-9(9) smime(16) modules(0) cms-2004(24) }

   DEFINITIONS IMPLICIT TAGS ::=
   BEGIN

   -- EXPORTS All
   -- The types and values defined in this module are exported for use
   -- in the other ASN.1 modules.  Other applications may use them for
   -- their own purposes.

   IMPORTS

     -- Imports from RFC 5280 [PROFILE], Appendix A.1
           AlgorithmIdentifier, Certificate, CertificateList,
           CertificateSerialNumber, Name
              FROM PKIX1Explicit88
                   { iso(1) identified-organization(3) dod(6)
                     internet(1) security(5) mechanisms(5) pkix(7)
                     mod(0) pkix1-explicit(18) }

     -- Imports from RFC 3281 [ACPROFILE], Appendix B
           AttributeCertificate
              FROM PKIXAttributeCertificate
                   { iso(1) identified-organization(3) dod(6)
                     internet(1) security(5) mechanisms(5) pkix(7)
                     mod(0) attribute-cert(12) }

     -- Imports from Appendix B of this document
           AttributeCertificateV1
              FROM AttributeCertificateVersion1
                   { iso(1) member-body(2) us(840) rsadsi(113549)
                     pkcs(1) pkcs-9(9) smime(16) modules(0)
                     v1AttrCert(15) } ;

   -- Cryptographic Message Syntax

   ContentInfo ::= SEQUENCE {
     contentType ContentType,
     content [0] EXPLICIT ANY DEFINED BY contentType }

   ContentType ::= OBJECT IDENTIFIER

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   SignedData ::= SEQUENCE {
     version CMSVersion,
     digestAlgorithms DigestAlgorithmIdentifiers,
     encapContentInfo EncapsulatedContentInfo,
     certificates [0] IMPLICIT CertificateSet OPTIONAL,
     crls [1] IMPLICIT RevocationInfoChoices OPTIONAL,
     signerInfos SignerInfos }

   DigestAlgorithmIdentifiers ::= SET OF DigestAlgorithmIdentifier

   SignerInfos ::= SET OF SignerInfo

   EncapsulatedContentInfo ::= SEQUENCE {
     eContentType ContentType,
     eContent [0] EXPLICIT OCTET STRING OPTIONAL }

   SignerInfo ::= SEQUENCE {
     version CMSVersion,
     sid SignerIdentifier,
     digestAlgorithm DigestAlgorithmIdentifier,
     signedAttrs [0] IMPLICIT SignedAttributes OPTIONAL,
     signatureAlgorithm SignatureAlgorithmIdentifier,
     signature SignatureValue,
     unsignedAttrs [1] IMPLICIT UnsignedAttributes OPTIONAL }

   SignerIdentifier ::= CHOICE {
     issuerAndSerialNumber IssuerAndSerialNumber,
     subjectKeyIdentifier [0] SubjectKeyIdentifier }

   SignedAttributes ::= SET SIZE (1..MAX) OF Attribute

   UnsignedAttributes ::= SET SIZE (1..MAX) OF Attribute

   Attribute ::= SEQUENCE {
     attrType OBJECT IDENTIFIER,
     attrValues SET OF AttributeValue }

   AttributeValue ::= ANY

   SignatureValue ::= OCTET STRING

   EnvelopedData ::= SEQUENCE {
     version CMSVersion,
     originatorInfo [0] IMPLICIT OriginatorInfo OPTIONAL,
     recipientInfos RecipientInfos,
     encryptedContentInfo EncryptedContentInfo,
     unprotectedAttrs [1] IMPLICIT UnprotectedAttributes OPTIONAL }

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   OriginatorInfo ::= SEQUENCE {
     certs [0] IMPLICIT CertificateSet OPTIONAL,
     crls [1] IMPLICIT RevocationInfoChoices OPTIONAL }

   RecipientInfos ::= SET SIZE (1..MAX) OF RecipientInfo

   EncryptedContentInfo ::= SEQUENCE {
     contentType ContentType,
     contentEncryptionAlgorithm ContentEncryptionAlgorithmIdentifier,
     encryptedContent [0] IMPLICIT EncryptedContent OPTIONAL }

   EncryptedContent ::= OCTET STRING

   UnprotectedAttributes ::= SET SIZE (1..MAX) OF Attribute

   RecipientInfo ::= CHOICE {
     ktri KeyTransRecipientInfo,
     kari [1] KeyAgreeRecipientInfo,
     kekri [2] KEKRecipientInfo,
     pwri [3] PasswordRecipientInfo,
     ori [4] OtherRecipientInfo }

   EncryptedKey ::= OCTET STRING

   KeyTransRecipientInfo ::= SEQUENCE {
     version CMSVersion,  -- always set to 0 or 2
     rid RecipientIdentifier,
     keyEncryptionAlgorithm KeyEncryptionAlgorithmIdentifier,
     encryptedKey EncryptedKey }

   RecipientIdentifier ::= CHOICE {
     issuerAndSerialNumber IssuerAndSerialNumber,
     subjectKeyIdentifier [0] SubjectKeyIdentifier }

   KeyAgreeRecipientInfo ::= SEQUENCE {
     version CMSVersion,  -- always set to 3
     originator [0] EXPLICIT OriginatorIdentifierOrKey,
     ukm [1] EXPLICIT UserKeyingMaterial OPTIONAL,
     keyEncryptionAlgorithm KeyEncryptionAlgorithmIdentifier,
     recipientEncryptedKeys RecipientEncryptedKeys }

   OriginatorIdentifierOrKey ::= CHOICE {
     issuerAndSerialNumber IssuerAndSerialNumber,
     subjectKeyIdentifier [0] SubjectKeyIdentifier,
     originatorKey [1] OriginatorPublicKey }

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   OriginatorPublicKey ::= SEQUENCE {
     algorithm AlgorithmIdentifier,
     publicKey BIT STRING }

   RecipientEncryptedKeys ::= SEQUENCE OF RecipientEncryptedKey

   RecipientEncryptedKey ::= SEQUENCE {
     rid KeyAgreeRecipientIdentifier,
     encryptedKey EncryptedKey }

   KeyAgreeRecipientIdentifier ::= CHOICE {
     issuerAndSerialNumber IssuerAndSerialNumber,
     rKeyId [0] IMPLICIT RecipientKeyIdentifier }

   RecipientKeyIdentifier ::= SEQUENCE {
     subjectKeyIdentifier SubjectKeyIdentifier,
     date GeneralizedTime OPTIONAL,
     other OtherKeyAttribute OPTIONAL }

   SubjectKeyIdentifier ::= OCTET STRING

   KEKRecipientInfo ::= SEQUENCE {
     version CMSVersion,  -- always set to 4
     kekid KEKIdentifier,
     keyEncryptionAlgorithm KeyEncryptionAlgorithmIdentifier,
     encryptedKey EncryptedKey }

   KEKIdentifier ::= SEQUENCE {
     keyIdentifier OCTET STRING,
     date GeneralizedTime OPTIONAL,
     other OtherKeyAttribute OPTIONAL }

   PasswordRecipientInfo ::= SEQUENCE {
     version CMSVersion,   -- always set to 0
     keyDerivationAlgorithm [0] KeyDerivationAlgorithmIdentifier
                                OPTIONAL,
     keyEncryptionAlgorithm KeyEncryptionAlgorithmIdentifier,
     encryptedKey EncryptedKey }

   OtherRecipientInfo ::= SEQUENCE {
     oriType OBJECT IDENTIFIER,
     oriValue ANY DEFINED BY oriType }

   DigestedData ::= SEQUENCE {
     version CMSVersion,
     digestAlgorithm DigestAlgorithmIdentifier,
     encapContentInfo EncapsulatedContentInfo,
     digest Digest }

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   Digest ::= OCTET STRING

   EncryptedData ::= SEQUENCE {
     version CMSVersion,
     encryptedContentInfo EncryptedContentInfo,
     unprotectedAttrs [1] IMPLICIT UnprotectedAttributes OPTIONAL }

   AuthenticatedData ::= SEQUENCE {
     version CMSVersion,
     originatorInfo [0] IMPLICIT OriginatorInfo OPTIONAL,
     recipientInfos RecipientInfos,
     macAlgorithm MessageAuthenticationCodeAlgorithm,
     digestAlgorithm [1] DigestAlgorithmIdentifier OPTIONAL,
     encapContentInfo EncapsulatedContentInfo,
     authAttrs [2] IMPLICIT AuthAttributes OPTIONAL,
     mac MessageAuthenticationCode,
     unauthAttrs [3] IMPLICIT UnauthAttributes OPTIONAL }

   AuthAttributes ::= SET SIZE (1..MAX) OF Attribute

   UnauthAttributes ::= SET SIZE (1..MAX) OF Attribute

   MessageAuthenticationCode ::= OCTET STRING

   DigestAlgorithmIdentifier ::= AlgorithmIdentifier

   SignatureAlgorithmIdentifier ::= AlgorithmIdentifier

   KeyEncryptionAlgorithmIdentifier ::= AlgorithmIdentifier

   ContentEncryptionAlgorithmIdentifier ::= AlgorithmIdentifier

   MessageAuthenticationCodeAlgorithm ::= AlgorithmIdentifier

   KeyDerivationAlgorithmIdentifier ::= AlgorithmIdentifier

   RevocationInfoChoices ::= SET OF RevocationInfoChoice

   RevocationInfoChoice ::= CHOICE {
     crl CertificateList,
     other [1] IMPLICIT OtherRevocationInfoFormat }

   OtherRevocationInfoFormat ::= SEQUENCE {
     otherRevInfoFormat OBJECT IDENTIFIER,
     otherRevInfo ANY DEFINED BY otherRevInfoFormat }

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   CertificateChoices ::= CHOICE {
     certificate Certificate,
     extendedCertificate [0] IMPLICIT ExtendedCertificate,  -- Obsolete
     v1AttrCert [1] IMPLICIT AttributeCertificateV1,        -- Obsolete
     v2AttrCert [2] IMPLICIT AttributeCertificateV2,
     other [3] IMPLICIT OtherCertificateFormat }

   AttributeCertificateV2 ::= AttributeCertificate

   OtherCertificateFormat ::= SEQUENCE {
     otherCertFormat OBJECT IDENTIFIER,
     otherCert ANY DEFINED BY otherCertFormat }

   CertificateSet ::= SET OF CertificateChoices

   IssuerAndSerialNumber ::= SEQUENCE {
     issuer Name,
     serialNumber CertificateSerialNumber }

   CMSVersion ::= INTEGER  { v0(0), v1(1), v2(2), v3(3), v4(4), v5(5) }

   UserKeyingMaterial ::= OCTET STRING

   OtherKeyAttribute ::= SEQUENCE {
     keyAttrId OBJECT IDENTIFIER,
     keyAttr ANY DEFINED BY keyAttrId OPTIONAL }

   -- Content Type Object Identifiers

   id-ct-contentInfo OBJECT IDENTIFIER ::= { iso(1) member-body(2)
       us(840) rsadsi(113549) pkcs(1) pkcs9(9) smime(16) ct(1) 6 }

   id-data OBJECT IDENTIFIER ::= { iso(1) member-body(2)
       us(840) rsadsi(113549) pkcs(1) pkcs7(7) 1 }

   id-signedData OBJECT IDENTIFIER ::= { iso(1) member-body(2)
       us(840) rsadsi(113549) pkcs(1) pkcs7(7) 2 }

   id-envelopedData OBJECT IDENTIFIER ::= { iso(1) member-body(2)
       us(840) rsadsi(113549) pkcs(1) pkcs7(7) 3 }

   id-digestedData OBJECT IDENTIFIER ::= { iso(1) member-body(2)
       us(840) rsadsi(113549) pkcs(1) pkcs7(7) 5 }

   id-encryptedData OBJECT IDENTIFIER ::= { iso(1) member-body(2)
       us(840) rsadsi(113549) pkcs(1) pkcs7(7) 6 }

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   id-ct-authData OBJECT IDENTIFIER ::= { iso(1) member-body(2)
       us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) ct(1) 2 }

   -- The CMS Attributes

   MessageDigest ::= OCTET STRING

   SigningTime  ::= Time

   Time ::= CHOICE {
     utcTime UTCTime,
     generalTime GeneralizedTime }

   Countersignature ::= SignerInfo

   -- Attribute Object Identifiers

   id-contentType OBJECT IDENTIFIER ::= { iso(1) member-body(2)
       us(840) rsadsi(113549) pkcs(1) pkcs9(9) 3 }

   id-messageDigest OBJECT IDENTIFIER ::= { iso(1) member-body(2)
       us(840) rsadsi(113549) pkcs(1) pkcs9(9) 4 }

   id-signingTime OBJECT IDENTIFIER ::= { iso(1) member-body(2)
       us(840) rsadsi(113549) pkcs(1) pkcs9(9) 5 }

   id-countersignature OBJECT IDENTIFIER ::= { iso(1) member-body(2)
       us(840) rsadsi(113549) pkcs(1) pkcs9(9) 6 }

   -- Obsolete Extended Certificate syntax from PKCS #6

   ExtendedCertificateOrCertificate ::= CHOICE {
     certificate Certificate,
     extendedCertificate [0] IMPLICIT ExtendedCertificate }

   ExtendedCertificate ::= SEQUENCE {
     extendedCertificateInfo ExtendedCertificateInfo,
     signatureAlgorithm SignatureAlgorithmIdentifier,
     signature Signature }

   ExtendedCertificateInfo ::= SEQUENCE {
     version CMSVersion,
     certificate Certificate,
     attributes UnauthAttributes }

   Signature ::= BIT STRING

   END -- of CryptographicMessageSyntax2004

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12.2.  Version 1 Attribute Certificate ASN.1 Module

   AttributeCertificateVersion1
       { iso(1) member-body(2) us(840) rsadsi(113549)
         pkcs(1) pkcs-9(9) smime(16) modules(0) v1AttrCert(15) }

   DEFINITIONS EXPLICIT TAGS ::=
   BEGIN

   -- EXPORTS All

   IMPORTS

     -- Imports from RFC 5280 [PROFILE], Appendix A.1
           AlgorithmIdentifier, Attribute, CertificateSerialNumber,
           Extensions, UniqueIdentifier
              FROM PKIX1Explicit88
                   { iso(1) identified-organization(3) dod(6)
                     internet(1) security(5) mechanisms(5) pkix(7)
                     mod(0) pkix1-explicit(18) }

     -- Imports from RFC 5280 [PROFILE], Appendix A.2
           GeneralNames
              FROM PKIX1Implicit88
                   { iso(1) identified-organization(3) dod(6)
                     internet(1) security(5) mechanisms(5) pkix(7)
                     mod(0) pkix1-implicit(19) }

     -- Imports from RFC 3281 [ACPROFILE], Appendix B
           AttCertValidityPeriod, IssuerSerial
              FROM PKIXAttributeCertificate
                   { iso(1) identified-organization(3) dod(6)
                     internet(1) security(5) mechanisms(5) pkix(7)
                     mod(0) attribute-cert(12) } ;

   -- Definition extracted from X.509-1997 [X.509-97], but
   -- different type names are used to avoid collisions.

   AttributeCertificateV1 ::= SEQUENCE {
     acInfo AttributeCertificateInfoV1,
     signatureAlgorithm AlgorithmIdentifier,
     signature BIT STRING }

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   AttributeCertificateInfoV1 ::= SEQUENCE {
     version AttCertVersionV1 DEFAULT v1,
     subject CHOICE {
       baseCertificateID [0] IssuerSerial,
         -- associated with a Public Key Certificate
       subjectName [1] GeneralNames },
         -- associated with a name
     issuer GeneralNames,
     signature AlgorithmIdentifier,
     serialNumber CertificateSerialNumber,
     attCertValidityPeriod AttCertValidityPeriod,
     attributes SEQUENCE OF Attribute,
     issuerUniqueID UniqueIdentifier OPTIONAL,
     extensions Extensions OPTIONAL }

   AttCertVersionV1 ::= INTEGER { v1(0) }

   END -- of AttributeCertificateVersion1

13.  References

13.1.  Normative References

   [ACPROFILE]   Farrell, S. and R. Housley, "An Internet Attribute
                 Certificate Profile for Authorization", RFC 3281, April
                 2002.

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

   [STDWORDS]    Bradner, S., "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.501-88]    CCITT.  Recommendation X.501: The Directory - Models,
                 1988.

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

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   [X.509-97]    ITU-T.  Recommendation X.509: The Directory -
                 Authentication Framework, 1997.

   [X.509-00]    ITU-T.  Recommendation X.509: The Directory -
                 Authentication Framework, 2000.

13.2.  Informative References

   [CMS1]        Housley, R., "Cryptographic Message Syntax", RFC 2630,
                 June 1999.

   [CMS2]        Housley, R., "Cryptographic Message Syntax (CMS)", RFC
                 3369, August 2002.

   [CMS3]        Housley, R., "Cryptographic Message Syntax (CMS)", RFC
                 3852, July 2004.

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

   [CMSMSIG]     Housley, R., "Cryptographic Message Syntax (CMS)
                 Multiple Signer Clarification", RFC 4853, April 2007.

   [DH-X9.42]    Rescorla, E., "Diffie-Hellman Key Agreement Method",
                 RFC 2631, June 1999.

   [ESS]         Hoffman, P., Ed., "Enhanced Security Services for
                 S/MIME", RFC 2634, June 1999.

   [MSAC]        Microsoft Development Network (MSDN) Library,
                 "Authenticode", April 2004 Release.

   [MSG2]        Dusse, S., Hoffman, P., Ramsdell, B., Lundblade, L.,
                 and L. Repka, "S/MIME Version 2 Message Specification",
                 RFC 2311, March 1998.

   [MSG3]        Ramsdell, B., Ed., "S/MIME Version 3 Message
                 Specification", RFC 2633, June 1999.

   [MSG3.1]      Ramsdell, B., Ed., "Secure/Multipurpose Internet Mail
                 Extensions (S/MIME) Version 3.1 Message Specification",
                 RFC 3851, July 2004.

   [NEWPKCS#1]   Kaliski, B. and J. Staddon, "PKCS #1: RSA Cryptography
                 Specifications Version 2.0", RFC 2437, October 1998.

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   [OCSP]        Myers, M., Ankney, R., Malpani, A., Galperin, S., and
                 C. Adams, "X.509 Internet Public Key Infrastructure
                 Online Certificate Status Protocol - OCSP", RFC 2560,
                 June 1999.

   [PKCS#1]      Kaliski, B., "PKCS #1: RSA Encryption Version 1.5", RFC
                 2313, March 1998.

   [PKCS#6]      RSA Laboratories.  PKCS #6: Extended-Certificate Syntax
                 Standard, Version 1.5.  November 1993.

   [PKCS#7]      Kaliski, B., "PKCS #7: Cryptographic Message Syntax
                 Version 1.5", RFC 2315, March 1998.

   [PKCS#9]      RSA Laboratories.  PKCS #9: Selected Attribute Types,
                 Version 1.1.  November 1993.

   [PWRI]        Gutmann, P., "Password-based Encryption for CMS", RFC
                 3211, December 2001.

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

14.  Security Considerations

   The Cryptographic Message Syntax provides a method for digitally
   signing data, digesting data, encrypting data, and authenticating
   data.

   Implementations must protect the signer's private key.  Compromise of
   the signer's private key permits masquerade.

   Implementations must protect the key management private key, the
   key-encryption key, and the content-encryption key.  Compromise of
   the key management private key or the key-encryption key may result
   in the disclosure of all contents protected with that key.
   Similarly, compromise of the content-encryption key may result in
   disclosure of the associated encrypted content.

   Implementations must protect the key management private key and the
   message-authentication key.  Compromise of the key management private
   key permits masquerade of authenticated data.  Similarly, compromise
   of the message-authentication key may result in undetectable
   modification of the authenticated content.

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   The key management technique employed to distribute message-
   authentication keys must itself provide data origin authentication;
   otherwise, the contents are delivered with integrity from an unknown
   source.  Neither RSA [PKCS#1] [NEWPKCS#1] nor Ephemeral-Static
   Diffie-Hellman [DH-X9.42] provide the necessary data origin
   authentication.  Static-Static Diffie-Hellman [DH-X9.42] does provide
   the necessary data origin authentication when both the originator and
   recipient public keys are bound to appropriate identities in X.509
   certificates.

   When more than two parties share the same message-authentication key,
   data origin authentication is not provided.  Any party that knows the
   message-authentication key can compute a valid MAC; therefore, the
   contents could originate from any one of the parties.

   Implementations must randomly generate content-encryption keys,
   message-authentication keys, initialization vectors (IVs), and
   padding.  Also, the generation of public/private key pairs relies on
   random numbers.  The use of inadequate pseudo-random number
   generators (PRNGs) to generate cryptographic keys can result in
   little or no security.  An attacker may find it much easier to
   reproduce the PRNG environment that produced the keys, searching the
   resulting small set of possibilities, rather than brute force
   searching the whole key space.  The generation of quality random
   numbers is difficult.  RFC 4086 [RANDOM] offers important guidance in
   this area.

   When using key-agreement algorithms or previously distributed
   symmetric key-encryption keys, a key-encryption key is used to
   encrypt the content-encryption key.  If the key-encryption and
   content-encryption algorithms are different, the effective security
   is determined by the weaker of the two algorithms.  If, for example,
   content is encrypted with Triple-DES using a 168-bit Triple-DES
   content-encryption key, and the content-encryption key is wrapped
   with RC2 using a 40-bit RC2 key-encryption key, then at most 40 bits
   of protection is provided.  A trivial search to determine the value
   of the 40-bit RC2 key can recover the Triple-DES key, and then the
   Triple-DES key can be used to decrypt the content.  Therefore,
   implementers must ensure that key-encryption algorithms are as strong
   or stronger than content-encryption algorithms.

   Implementers should be aware that cryptographic algorithms become
   weaker with time.  As new cryptoanalysis techniques are developed and
   computing performance improves, the work factor to break a particular
   cryptographic algorithm will be reduced.  Therefore, cryptographic
   algorithm implementations should be modular, allowing new algorithms
   to be readily inserted.  That is, implementers should be prepared for
   the set of algorithms that must be supported to change over time.

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   The countersignature unsigned attribute includes a digital signature
   that is computed on the content signature value; thus, the
   countersigning process need not know the original signed content.
   This structure permits implementation efficiency advantages; however,
   this structure may also permit the countersigning of an inappropriate
   signature value.  Therefore, implementations that perform
   countersignatures should either verify the original signature value
   prior to countersigning it (this verification requires processing of
   the original content), or implementations should perform
   countersigning in a context that ensures that only appropriate
   signature values are countersigned.

15.  Acknowledgments

   This document is the result of contributions from many professionals.
   I appreciate the hard work of all members of the IETF S/MIME Working
   Group.  I extend a special thanks to Rich Ankney, Simon Blake-Wilson,
   Tim Dean, Steve Dusse, Carl Ellison, Peter Gutmann, Bob Jueneman,
   Stephen Henson, Paul Hoffman, Scott Hollenbeck, Don Johnson, Burt
   Kaliski, John Linn, John Pawling, Blake Ramsdell, Francois Rousseau,
   Jim Schaad, Dave Solo, Paul Timmel, and Sean Turner for their efforts
   and support.

   I thank Tim Polk for his encouragement in advancing this
   specification along the standards maturity ladder.  In addition, I
   thank Jan Vilhuber for the careful reading that resulted in RFC
   Errata 1744.

Author's Address

   Russell Housley
   Vigil Security, LLC
   918 Spring Knoll Drive
   Herndon, VA 20170
   USA
   EMail: housley@vigilsec.com