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RFC 5652

Cryptographic Message Syntax (CMS)

Pages: 56
Internet Standard: 70
Errata
Obsoletes:  3852
Updated by:  8933
Part 3 of 3 – Pages 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