tech-invite   World Map     

IETF     RFCs     Groups     SIP     ABNFs    |    3GPP     Specs     Glossaries     Architecture     IMS     UICC    |    search

RFC 2630

 
 
 

Cryptographic Message Syntax

Part 2 of 2, p. 28 to 60
Prev RFC Part

 


prevText      Top      Up      ToC       Page 28 
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  CertificateRevocationLists

   The CertificateRevocationLists type gives a set of certificate
   revocation lists (CRLs). It is intended that the set contain
   information sufficient to determine whether the certificates and

Top      Up      ToC       Page 29 
   attribute certificates with which the set is associated are revoked
   or not.  However, there may be more CRLs than necessary or there may
   be fewer CRLs than necessary.

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

   CRLs are specified in X.509 [X.509-97], and they are profiled for use
   in the Internet in RFC 2459 [PROFILE].

   The definition of CertificateList is imported from X.509.

      CertificateRevocationLists ::= SET OF CertificateList

10.2.2  CertificateChoices

   The CertificateChoices type gives either a PKCS #6 extended
   certificate [PKCS#6], an X.509 certificate, or an X.509 attribute
   certificate [X.509-97].  The PKCS #6 extended certificate is
   obsolete.  PKCS #6 certificates are included for backward
   compatibility, and their use should be avoided.  The Internet profile
   of X.509 certificates is specified in the "Internet X.509 Public Key
   Infrastructure: Certificate and CRL Profile" [PROFILE].

   The definitions of Certificate and AttributeCertificate are imported
   from X.509.

      CertificateChoices ::= CHOICE {
         certificate Certificate,                 -- See X.509
         extendedCertificate [0] IMPLICIT ExtendedCertificate,
                                                  -- Obsolete
         attrCert [1] IMPLICIT AttributeCertificate }
                                                  -- See X.509 and X9.57

10.2.3  CertificateSet

   The CertificateSet type provides a set of certificates.  It is
   intended that the set be sufficient to contain chains 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 "chain" is outside the scope of this
   document.  Some applications may impose upper limits on the length of
   a chain; others may enforce certain relationships between the
   subjects and issuers of certificates within a chain.

Top      Up      ToC       Page 30 
      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 imported from X.501 [X.501-88], and the
   definition of CertificateSerialNumber is imported from X.509
   [X.509-97].

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

      CertificateSerialNumber ::= INTEGER

10.2.5  CMSVersion

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

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

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 may impede interoperability.

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

Top      Up      ToC       Page 31 
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 2459 [PROFILE].
   Some of the attributes defined in this section were originally
   defined in PKCS #9 [PKCS#9], others were not previously defined.  The
   attributes are not listed in any particular order.

   Additional attributes are defined in many places, notably the S/MIME
   Version 3 Message Specification [MSG] and the Enhanced Security
   Services for S/MIME [ESS], which also include recommendations on the
   placement of these attributes.

11.1  Content Type

   The content-type attribute type specifies the content type of the
   ContentInfo value being signed in signed-data.  The content-type
   attribute type is required if there are any authenticated attributes
   present.

   The content-type attribute must be a signed attribute or an
   authenticated attribute; it cannot be an unsigned attribute, an
   unauthenticated attribute, or an unprotectedAttribute.

   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

   A content-type 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 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.

Top      Up      ToC       Page 32 
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 is
   required if there are any attributes present.  Within authenticated-
   data, the message-digest authenticated attribute type is required if
   there are any attributes present.

   The message-digest attribute must be a signed attribute or an
   authenticated attribute; it cannot be an unsigned attribute or an
   unauthenticated 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 is defined as a SET OF Attributes.  The
   SignedAttributes in a signerInfo must not include multiple instances
   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 may be a signed attribute; it cannot be an
   unsigned attribute, an authenticated attribute, or an unauthenticated
   attribute.

Top      Up      ToC       Page 33 
   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 }

   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 Greenwich Mean Time (Zulu) and
   must include seconds (i.e., times are YYMMDDHHMMSSZ), even where the
   number of seconds is zero.  Midnight (GMT) 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 shall be
      interpreted as 19YY; and

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

   GeneralizedTime values shall be expressed in Greenwich Mean Time
   (Zulu) 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 is defined as a SET OF Attributes.  The
   SignedAttributes in a signerInfo 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,

Top      Up      ToC       Page 34 
   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 DER encoding of the signatureValue
   field of a SignerInfo value in signed-data.  Thus, the
   countersignature attribute type countersigns (signs in serial)
   another signature.

   The countersignature attribute must be an unsigned attribute; it
   cannot be a signed attribute, an authenticated attribute, or an
   unauthenticated 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 contain a message-digest
      attribute if it contains any other attributes, but need not
      contain a content-type attribute, as there is no content type for
      countersignatures.

      2.  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
   arbitrarily long series of countersignatures.

Top      Up      ToC       Page 35 
12  Supported Algorithms

   This section lists the algorithms that must be implemented.
   Additional algorithms that should be implemented are also included.

12.1  Digest Algorithms

   CMS implementations must include SHA-1.  CMS implementations should
   include MD5.

   Digest algorithm identifiers are located in the SignedData
   digestAlgorithms field, the SignerInfo digestAlgorithm field, the
   DigestedData digestAlgorithm field, and the AuthenticatedData
   digestAlgorithm field.

   Digest values are located in the DigestedData digest field, and
   digest values are located in the Message Digest authenticated
   attribute.  In addition, digest values are input to signature
   algorithms.

12.1.1  SHA-1

   The SHA-1 digest algorithm is defined in FIPS Pub 180-1 [SHA1]. The
   algorithm identifier for SHA-1 is:

      sha-1 OBJECT IDENTIFIER ::= { iso(1) identified-organization(3)
          oiw(14) secsig(3) algorithm(2) 26 }

   The AlgorithmIdentifier parameters field is optional.  If present,
   the parameters field must contain an ASN.1 NULL.  Implementations
   should accept SHA-1 AlgorithmIdentifiers with absent parameters as
   well as NULL parameters.  Implementations should generate SHA-1
   AlgorithmIdentifiers with NULL parameters.

12.1.2  MD5

   The MD5 digest algorithm is defined in RFC 1321 [MD5].  The algorithm
   identifier for MD5 is:

      md5 OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840)
          rsadsi(113549) digestAlgorithm(2) 5 }

   The AlgorithmIdentifier parameters field must be present, and the
   parameters field must contain NULL.  Implementations may accept the
   MD5 AlgorithmIdentifiers with absent parameters as well as NULL
   parameters.

Top      Up      ToC       Page 36 
12.2  Signature Algorithms

   CMS implementations must include DSA.  CMS implementations may
   include RSA.

   Signature algorithm identifiers are located in the SignerInfo
   signatureAlgorithm field.  Also, signature algorithm identifiers are
   located in the SignerInfo signatureAlgorithm field of
   countersignature attributes.

   Signature values are located in the SignerInfo signature field.
   Also, signature values are located in the SignerInfo signature field
   of countersignature attributes.

12.2.1  DSA

   The DSA signature algorithm is defined in FIPS Pub 186 [DSS].  DSA is
   always used with the SHA-1 message digest algorithm.  The algorithm
   identifier for DSA is:

      id-dsa-with-sha1 OBJECT IDENTIFIER ::=  { iso(1) member-body(2)
          us(840) x9-57 (10040) x9cm(4) 3 }

   The AlgorithmIdentifier parameters field must not be present.

12.2.2  RSA

   The RSA signature algorithm is defined in RFC 2347 [NEWPKCS#1]. RFC
   2347 specifies the use of the RSA signature algorithm with the SHA-1
   and MD5 message digest algorithms.  The algorithm identifier for RSA
   is:

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

12.3  Key Management Algorithms

   CMS accommodates three general key management techniques: key
   agreement, key transport, and previously distributed symmetric key-
   encryption keys.

12.3.1  Key Agreement Algorithms

   CMS implementations must include key agreement using X9.42
   Ephemeral-Static Diffie-Hellman.

   Any symmetric encryption algorithm that a CMS implementation includes
   as a content-encryption algorithm must also be included as a key-

Top      Up      ToC       Page 37 
   encryption algorithm.  CMS implementations must include key agreement
   of Triple-DES pairwise key-encryption keys and Triple-DES wrapping of
   Triple-DES content-encryption keys.  CMS implementations should
   include key agreement of RC2 pairwise key-encryption keys and RC2
   wrapping of RC2 content-encryption keys.  The key wrap algorithm for
   Triple-DES and RC2 is described in section 12.3.3.

   A CMS implementation may support mixed key-encryption and content-
   encryption algorithms.  For example, a 128-bit RC2 content-encryption
   key may be wrapped with 168-bit Triple-DES key-encryption key.
   Similarly, a 40-bit RC2 content-encryption key may be wrapped with
   128-bit RC2 key-encryption key.

   For key agreement of RC2 key-encryption keys, 128 bits must be
   generated as input to the key expansion process used to compute the
   RC2 effective key [RC2].

   Key agreement algorithm identifiers are located in the EnvelopedData
   RecipientInfos KeyAgreeRecipientInfo keyEncryptionAlgorithm and
   AuthenticatedData RecipientInfos KeyAgreeRecipientInfo
   keyEncryptionAlgorithm fields.

   Key wrap algorithm identifiers are located in the KeyWrapAlgorithm
   parameters within the EnvelopedData RecipientInfos
   KeyAgreeRecipientInfo keyEncryptionAlgorithm and AuthenticatedData
   RecipientInfos KeyAgreeRecipientInfo keyEncryptionAlgorithm fields.

   Wrapped content-encryption keys are located in the EnvelopedData
   RecipientInfos KeyAgreeRecipientInfo RecipientEncryptedKeys
   encryptedKey field.  Wrapped message-authentication keys are located
   in the AuthenticatedData RecipientInfos KeyAgreeRecipientInfo
   RecipientEncryptedKeys encryptedKey field.

12.3.1.1  X9.42 Ephemeral-Static Diffie-Hellman

   Ephemeral-Static Diffie-Hellman key agreement is defined in RFC 2631
   [DH-X9.42].  When using Ephemeral-Static Diffie-Hellman, the
   EnvelopedData RecipientInfos KeyAgreeRecipientInfo and
   AuthenticatedData RecipientInfos KeyAgreeRecipientInfo fields are
   used as follows:

      version must be 3.

      originator must be the originatorKey alternative.  The
      originatorKey algorithm fields must contain the dh-public-number
      object identifier with absent parameters.  The originatorKey
      publicKey field must contain the sender's ephemeral public key.
      The dh-public-number object identifier is:

Top      Up      ToC       Page 38 
         dh-public-number OBJECT IDENTIFIER ::= { iso(1) member-body(2)
             us(840) ansi-x942(10046) number-type(2) 1 }

      ukm may be absent.  When present, the ukm is used to ensure that a
      different key-encryption key is generated when the ephemeral
      private key might be used more than once.

      keyEncryptionAlgorithm must be the id-alg-ESDH algorithm
      identifier.  The algorithm identifier parameter field for id-alg-
      ESDH is KeyWrapAlgorihtm, and this parameter must be present.  The
      KeyWrapAlgorithm denotes the symmetric encryption algorithm used
      to encrypt the content-encryption key with the pairwise key-
      encryption key generated using the Ephemeral-Static Diffie-Hellman
      key agreement algorithm.  Triple-DES and RC2 key wrap algorithms
      are discussed in section 12.3.3.  The id-alg-ESDH algorithm
      identifier and parameter syntax is:

       id-alg-ESDH OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840)
           rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) alg(3) 5 }

       KeyWrapAlgorithm ::= AlgorithmIdentifier

      recipientEncryptedKeys contains an identifier and an encrypted key
      for each recipient.  The RecipientEncryptedKey
      KeyAgreeRecipientIdentifier must contain either the
      issuerAndSerialNumber identifying the recipient's certificate or
      the RecipientKeyIdentifier containing the subject key identifier
      from the recipient's certificate.  In both cases, the recipient's
      certificate contains the recipient's static public key.
      RecipientEncryptedKey EncryptedKey must contain the content-
      encryption key encrypted with the Ephemeral-Static Diffie-Hellman
      generated pairwise key-encryption key using the algorithm
      specified by the KeyWrapAlgortihm.

12.3.2  Key Transport Algorithms

   CMS implementations should include key transport using RSA.  RSA
   implementations must include key transport of Triple-DES content-
   encryption keys.  RSA implementations should include key transport of
   RC2 content-encryption keys.

   Key transport algorithm identifiers are located in the EnvelopedData
   RecipientInfos KeyTransRecipientInfo keyEncryptionAlgorithm and
   AuthenticatedData RecipientInfos KeyTransRecipientInfo
   keyEncryptionAlgorithm fields.

   Key transport encrypted content-encryption keys are located in the
   EnvelopedData RecipientInfos KeyTransRecipientInfo encryptedKey

Top      Up      ToC       Page 39 
   field.  Key transport encrypted message-authentication keys are
   located in the AuthenticatedData RecipientInfos KeyTransRecipientInfo
   encryptedKey field.

12.3.2.1  RSA

   The RSA key transport algorithm is the RSA encryption scheme defined
   in RFC 2313 [PKCS#1], block type is 02, where the message to be
   encrypted is the content-encryption key.  The algorithm identifier
   for RSA is:

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

   The AlgorithmIdentifier parameters field must be present, and the
   parameters field must contain NULL.

   When using a Triple-DES content-encryption key, adjust the parity
   bits for each DES key comprising the Triple-DES key prior to RSA
   encryption.

   The use of RSA encryption, as defined in RFC 2313 [PKCS#1], to
   provide confidentiality has a known vulnerability concerns.  The
   vulnerability is primarily relevant to usage in interactive
   applications rather than to store-and-forward environments.  Further
   information and proposed countermeasures are discussed in the
   Security Considerations section of this document.

   Note that the same encryption scheme is also defined in RFC 2437
   [NEWPKCS#1].  Within RFC 2437, this scheme is called
   RSAES-PKCS1-v1_5.

12.3.3  Symmetric Key-Encryption Key Algorithms

   CMS implementations may include symmetric key-encryption key
   management.  Such CMS implementations must include Triple-DES key-
   encryption keys wrapping Triple-DES content-encryption keys, and such
   CMS implementations should include RC2 key-encryption keys wrapping
   RC2 content-encryption keys.  Only 128-bit RC2 keys may be used as
   key-encryption keys, and they must be used with the
   RC2ParameterVersion parameter set to 58.  A CMS implementation may
   support mixed key-encryption and content-encryption algorithms.  For
   example, a 40-bit RC2 content-encryption key may be wrapped with
   168-bit Triple-DES key-encryption key or with a 128-bit RC2 key-
   encryption key.

Top      Up      ToC       Page 40 
   Key wrap algorithm identifiers are located in the EnvelopedData
   RecipientInfos KEKRecipientInfo keyEncryptionAlgorithm and
   AuthenticatedData RecipientInfos KEKRecipientInfo
   keyEncryptionAlgorithm fields.

   Wrapped content-encryption keys are located in the EnvelopedData
   RecipientInfos KEKRecipientInfo encryptedKey field.  Wrapped
   message-authentication keys are located in the AuthenticatedData
   RecipientInfos KEKRecipientInfo encryptedKey field.

   The output of a key agreement algorithm is a key-encryption key, and
   this key-encryption key is used to encrypt the content-encryption
   key.  In conjunction with key agreement algorithms, CMS
   implementations must include encryption of content-encryption keys
   with the pairwise key-encryption key generated using a key agreement
   algorithm.  To support key agreement, key wrap algorithm identifiers
   are located in the KeyWrapAlgorithm parameter of the EnvelopedData
   RecipientInfos KeyAgreeRecipientInfo keyEncryptionAlgorithm and
   AuthenticatedData RecipientInfos KeyAgreeRecipientInfo
   keyEncryptionAlgorithm fields.  Wrapped content-encryption keys are
   located in the EnvelopedData RecipientInfos KeyAgreeRecipientInfo
   RecipientEncryptedKeys encryptedKey field, wrapped message-
   authentication keys are located in the AuthenticatedData
   RecipientInfos KeyAgreeRecipientInfo RecipientEncryptedKeys
   encryptedKey field.

12.3.3.1  Triple-DES Key Wrap

   Triple-DES key encryption has the algorithm identifier:

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

   The AlgorithmIdentifier parameter field must be NULL.

   The key wrap algorithm used to encrypt a Triple-DES content-
   encryption key with a Triple-DES key-encryption key is specified in
   section 12.6.

   Out-of-band distribution of the Triple-DES key-encryption key used to
   encrypt the Triple-DES content-encryption key is beyond of the scope
   of this document.

Top      Up      ToC       Page 41 
12.3.3.2  RC2 Key Wrap

   RC2 key encryption has the algorithm identifier:

      id-alg-CMSRC2wrap OBJECT IDENTIFIER ::= { iso(1) member-body(2)
          us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) alg(3) 7 }

   The AlgorithmIdentifier parameter field must be RC2wrapParameter:

      RC2wrapParameter ::= RC2ParameterVersion

      RC2ParameterVersion ::= INTEGER

   The RC2 effective-key-bits (key size) greater than 32 and less than
   256 is encoded in the RC2ParameterVersion.  For the effective-key-
   bits of 40, 64, and 128, the rc2ParameterVersion values are 160, 120,
   and 58 respectively.  These values are not simply the RC2 key length.
   Note that the value 160 must be encoded as two octets (00 A0),
   because the one octet (A0) encoding represents a negative number.

   Only 128-bit RC2 keys may be used as key-encryption keys, and they
   must be used with the RC2ParameterVersion parameter set to 58.

   The key wrap algorithm used to encrypt a RC2 content-encryption key
   with a RC2 key-encryption key is specified in section 12.6.

   Out-of-band distribution of the RC2 key-encryption key used to
   encrypt the RC2 content-encryption key is beyond of the scope of this
   document.

12.4  Content Encryption Algorithms

   CMS implementations must include Triple-DES in CBC mode.  CMS
   implementations should include RC2 in CBC mode.

   Content encryption algorithms identifiers are located in the
   EnvelopedData EncryptedContentInfo contentEncryptionAlgorithm and the
   EncryptedData EncryptedContentInfo contentEncryptionAlgorithm fields.

   Content encryption algorithms are used to encipher the content
   located in the EnvelopedData EncryptedContentInfo encryptedContent
   field and the EncryptedData EncryptedContentInfo encryptedContent
   field.

Top      Up      ToC       Page 42 
12.4.1  Triple-DES CBC

   The Triple-DES algorithm is described in ANSI X9.52 [3DES].  The
   Triple-DES is composed from three sequential DES [DES] operations:
   encrypt, decrypt, and encrypt.  Three-Key Triple-DES uses a different
   key for each DES operation.  Two-Key Triple-DES uses one key for the
   two encrypt operations and different key for the decrypt operation.
   The same algorithm identifiers are used for Three-Key Triple-DES and
   Two-Key Triple-DES.  The algorithm identifier for Triple-DES in
   Cipher Block Chaining (CBC) mode is:

      des-ede3-cbc OBJECT IDENTIFIER ::= { iso(1) member-body(2)
          us(840) rsadsi(113549) encryptionAlgorithm(3) 7 }

   The AlgorithmIdentifier parameters field must be present, and the
   parameters field must contain a CBCParameter:

      CBCParameter ::= IV

      IV ::= OCTET STRING  -- exactly 8 octets

12.4.2  RC2 CBC

   The RC2 algorithm is described in RFC 2268 [RC2].  The algorithm
   identifier for RC2 in CBC mode is:

      rc2-cbc OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840)
          rsadsi(113549) encryptionAlgorithm(3) 2 }

   The AlgorithmIdentifier parameters field must be present, and the
   parameters field must contain a RC2CBCParameter:

      RC2CBCParameter ::= SEQUENCE {
        rc2ParameterVersion INTEGER,
        iv OCTET STRING  }  -- exactly 8 octets

   The RC2 effective-key-bits (key size) greater than 32 and less than
   256 is encoded in the rc2ParameterVersion.  For the effective-key-
   bits of 40, 64, and 128, the rc2ParameterVersion values are 160, 120,
   and 58 respectively.  These values are not simply the RC2 key length.
   Note that the value 160 must be encoded as two octets (00 A0), since
   the one octet (A0) encoding represents a negative number.

12.5  Message Authentication Code Algorithms

   CMS implementations that support authenticatedData must include HMAC
   with SHA-1.

Top      Up      ToC       Page 43 
   MAC algorithm identifiers are located in the AuthenticatedData
   macAlgorithm field.

   MAC values are located in the AuthenticatedData mac field.

12.5.1  HMAC with SHA-1

   The HMAC with SHA-1 algorithm is described in RFC 2104 [HMAC].  The
   algorithm identifier for HMAC with SHA-1 is:

      hMAC-SHA1 OBJECT IDENTIFIER ::= { iso(1) identified-organization(3)
          dod(6) internet(1) security(5) mechanisms(5) 8 1 2 }

   The AlgorithmIdentifier parameters field must be absent.

12.6  Triple-DES and RC2 Key Wrap Algorithms

   CMS implementations must include encryption of a Triple-DES content-
   encryption key with a Triple-DES key-encryption key using the
   algorithm specified in Sections 12.6.2 and 12.6.3.  CMS
   implementations should include encryption of a RC2 content-encryption
   key with a RC2 key-encryption key using the algorithm specified in
   Sections 12.6.4 and 12.6.5.  Triple-DES and RC2 content-encryption
   keys are encrypted in Cipher Block Chaining (CBC) mode [MODES].

   Key Transport algorithms allow for the content-encryption key to be
   directly encrypted; however, key agreement and symmetric key-
   encryption key algorithms encrypt the content-encryption key with a
   second symmetric encryption algorithm.  This section describes how
   the Triple-DES or RC2 content-encryption key is formatted and
   encrypted.

   Key agreement algorithms generate a pairwise key-encryption key, and
   a key wrap algorithm is used to encrypt the content-encryption key
   with the pairwise key-encryption key.  Similarly, a key wrap
   algorithm is used to encrypt the content-encryption key in a
   previously distributed key-encryption key.

   The key-encryption key is generated by the key agreement algorithm or
   distributed out of band.  For key agreement of RC2 key-encryption
   keys, 128 bits must be generated as input to the key expansion
   process used to compute the RC2 effective key [RC2].

   The same algorithm identifier is used for both 2-key and 3-key
   Triple-DES.  When the length of the content-encryption key to be
   wrapped is a 2-key Triple-DES key, a third key with the same value as
   the first key is created.  Thus, all Triple-DES content-encryption
   keys are wrapped like 3-key Triple-DES keys.

Top      Up      ToC       Page 44 
12.6.1  Key Checksum

   The CMS Checksum Algorithm is used to provide a content-encryption
   key integrity check value.  The algorithm is:

   1.  Compute a 20 octet SHA-1 [SHA1] message digest on the
       content-encryption key.
   2.  Use the most significant (first) eight octets of the message
       digest value as the checksum value.

12.6.2  Triple-DES Key Wrap

   The Triple-DES key wrap algorithm encrypts a Triple-DES content-
   encryption key with a Triple-DES key-encryption key.  The Triple-DES
   key wrap algorithm is:

   1.  Set odd parity for each of the DES key octets comprising
       the content-encryption key, call the result CEK.
   2.  Compute an 8 octet key checksum value on CEK as described above
       in Section 12.6.1, call the result ICV.
   3.  Let CEKICV = CEK || ICV.
   4.  Generate 8 octets at random, call the result IV.
   5.  Encrypt CEKICV in CBC mode using the key-encryption key.  Use
       the random value generated in the previous step as the
       initialization vector (IV).  Call the ciphertext TEMP1.
   6.  Let TEMP2 = IV || TEMP1.
   7.  Reverse the order of the octets in TEMP2.  That is, the most
       significant (first) octet is swapped with the least significant
       (last) octet, and so on.  Call the result TEMP3.
   8.  Encrypt TEMP3 in CBC mode using the key-encryption key.  Use
       an initialization vector (IV) of 0x4adda22c79e82105.
       The ciphertext is 40 octets long.

   Note:  When the same content-encryption key is wrapped in different
   key-encryption keys, a fresh initialization vector (IV) must be
   generated for each invocation of the key wrap algorithm.

12.6.3  Triple-DES Key Unwrap

   The Triple-DES key unwrap algorithm decrypts a Triple-DES content-
   encryption key using a Triple-DES key-encryption key.  The Triple-DES
   key unwrap algorithm is:

   1.  If the wrapped content-encryption key is not 40 octets, then
       error.
   2.  Decrypt the wrapped content-encryption key in CBC mode using
       the key-encryption key.  Use an initialization vector (IV)
       of 0x4adda22c79e82105.  Call the output TEMP3.

Top      Up      ToC       Page 45 
   3.  Reverse the order of the octets in TEMP3.  That is, the most
       significant (first) octet is swapped with the least significant
       (last) octet, and so on.  Call the result TEMP2.
   4.  Decompose the TEMP2 into IV and TEMP1.  IV is the most
       significant (first) 8 octets, and TEMP1 is the least significant
       (last) 32 octets.
   5.  Decrypt TEMP1 in CBC mode using the key-encryption key.  Use
       the IV value from the previous step as the initialization vector.
       Call the ciphertext CEKICV.
   6.  Decompose the CEKICV into CEK and ICV. CEK is the most significant
       (first) 24 octets, and ICV is the least significant (last) 8 octets.
   7.  Compute an 8 octet key checksum value on CEK as described above
       in Section 12.6.1.  If the computed key checksum value does not
       match the decrypted key checksum value, ICV, then error.
   8.  Check for odd parity each of the DES key octets comprising CEK.
       If parity is incorrect, then there is an error.
   9.  Use CEK as the content-encryption key.

12.6.4  RC2 Key Wrap

   The RC2 key wrap algorithm encrypts a RC2 content-encryption key with
   a RC2 key-encryption key.  The RC2 key wrap algorithm is:

   1.  Let the content-encryption key be called CEK, and let the length
       of the content-encryption key in octets be called LENGTH.  LENGTH
       is a single octet.
   2.  Let LCEK = LENGTH || CEK.
   3.  Let LCEKPAD = LCEK || PAD.  If the length of LCEK is a multiple
       of 8, the PAD has a length of zero.  If the length of LCEK is
       not a multiple of 8, then PAD contains the fewest number of
       random octets to make the length of LCEKPAD a multiple of 8.
   4.  Compute an 8 octet key checksum value on LCEKPAD as described
       above in Section 12.6.1, call the result ICV.
   5.  Let LCEKPADICV = LCEKPAD || ICV.
   6.  Generate 8 octets at random, call the result IV.
   7.  Encrypt LCEKPADICV in CBC mode using the key-encryption key.
       Use the random value generated in the previous step as the
       initialization vector (IV).  Call the ciphertext TEMP1.
   8.  Let TEMP2 = IV || TEMP1.
   9.  Reverse the order of the octets in TEMP2.  That is, the most
       significant (first) octet is swapped with the least significant
       (last) octet, and so on.  Call the result TEMP3.
   10. Encrypt TEMP3 in CBC mode using the key-encryption key.  Use
       an initialization vector (IV) of 0x4adda22c79e82105.

   Note:  When the same content-encryption key is wrapped in different
   key-encryption keys, a fresh initialization vector (IV) must be
   generated for each invocation of the key wrap algorithm.

Top      Up      ToC       Page 46 
12.6.5  RC2 Key Unwrap

   The RC2 key unwrap algorithm decrypts a RC2 content-encryption key
   using a RC2 key-encryption key.  The RC2 key unwrap algorithm is:

   1.  If the wrapped content-encryption key is not a multiple of 8
       octets, then error.
   2.  Decrypt the wrapped content-encryption key in CBC mode using
       the key-encryption key.  Use an initialization vector (IV)
       of 0x4adda22c79e82105.  Call the output TEMP3.
   3.  Reverse the order of the octets in TEMP3.  That is, the most
       significant (first) octet is swapped with the least significant
       (last) octet, and so on.  Call the result TEMP2.
   4.  Decompose the TEMP2 into IV and TEMP1.  IV is the most
       significant (first) 8 octets, and TEMP1 is the remaining octets.

   5.  Decrypt TEMP1 in CBC mode using the key-encryption key.  Use
       the IV value from the previous step as the initialization vector.
       Call the plaintext LCEKPADICV.
   6.  Decompose the LCEKPADICV into LCEKPAD, and ICV.  ICV is the
       least significant (last) octet 8 octets.  LCEKPAD is the
       remaining octets.
   7.  Compute an 8 octet key checksum value on LCEKPAD as described
       above in Section 12.6.1.  If the computed key checksum value
       does not match the decrypted key checksum value, ICV, then error.
   8.  Decompose the LCEKPAD into LENGTH, CEK, and PAD.  LENGTH is the
       most significant (first) octet.  CEK is the following LENGTH
       octets.  PAD is the remaining octets, if any.
   9.  If the length of PAD is more than 7 octets, then error.
   10. Use CEK as the content-encryption key.

Top      Up      ToC       Page 47 
Appendix A:  ASN.1 Module

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

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

  -- Directory Information Framework (X.501)
        Name
           FROM InformationFramework { joint-iso-itu-t ds(5) modules(1)
                informationFramework(1) 3 }

  -- Directory Authentication Framework (X.509)
        AlgorithmIdentifier, AttributeCertificate, Certificate,
        CertificateList, CertificateSerialNumber
           FROM AuthenticationFramework { joint-iso-itu-t ds(5)
                module(1) authenticationFramework(7) 3 } ;


-- Cryptographic Message Syntax

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

ContentType ::= OBJECT IDENTIFIER

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

DigestAlgorithmIdentifiers ::= SET OF DigestAlgorithmIdentifier

SignerInfos ::= SET OF SignerInfo

Top      Up      ToC       Page 48 
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 }

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

RecipientInfos ::= SET OF RecipientInfo

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

EncryptedContent ::= OCTET STRING

Top      Up      ToC       Page 49 
UnprotectedAttributes ::= SET SIZE (1..MAX) OF Attribute

RecipientInfo ::= CHOICE {
  ktri KeyTransRecipientInfo,
  kari [1] KeyAgreeRecipientInfo,
  kekri [2] KEKRecipientInfo }

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 }

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 }

Top      Up      ToC       Page 50 
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 }

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

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,
  authenticatedAttributes [2] IMPLICIT AuthAttributes OPTIONAL,
  mac MessageAuthenticationCode,
  unauthenticatedAttributes [3] IMPLICIT UnauthAttributes OPTIONAL }

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

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

MessageAuthenticationCode ::= OCTET STRING

Top      Up      ToC       Page 51 
DigestAlgorithmIdentifier ::= AlgorithmIdentifier

SignatureAlgorithmIdentifier ::= AlgorithmIdentifier

KeyEncryptionAlgorithmIdentifier ::= AlgorithmIdentifier

ContentEncryptionAlgorithmIdentifier ::= AlgorithmIdentifier

MessageAuthenticationCodeAlgorithm ::= AlgorithmIdentifier

CertificateRevocationLists ::= SET OF CertificateList

CertificateChoices ::= CHOICE {
  certificate Certificate,  -- See X.509
  extendedCertificate [0] IMPLICIT ExtendedCertificate,  -- Obsolete
  attrCert [1] IMPLICIT AttributeCertificate }  -- See X.509 & X9.57

CertificateSet ::= SET OF CertificateChoices

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

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

UserKeyingMaterial ::= OCTET STRING

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


-- CMS Attributes

MessageDigest ::= OCTET STRING

SigningTime  ::= Time

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

Countersignature ::= SignerInfo

Top      Up      ToC       Page 52 
-- Algorithm Identifiers

sha-1 OBJECT IDENTIFIER ::= { iso(1) identified-organization(3)
    oiw(14) secsig(3) algorithm(2) 26 }

md5 OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840)
    rsadsi(113549) digestAlgorithm(2) 5 }

id-dsa-with-sha1 OBJECT IDENTIFIER ::=  { iso(1) member-body(2)
    us(840) x9-57 (10040) x9cm(4) 3 }

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

dh-public-number OBJECT IDENTIFIER ::= { iso(1) member-body(2)
    us(840) ansi-x942(10046) number-type(2) 1 }

id-alg-ESDH OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840)
    rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) alg(3) 5 }

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

id-alg-CMSRC2wrap OBJECT IDENTIFIER ::= { iso(1) member-body(2)
    us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) alg(3) 7 }

des-ede3-cbc OBJECT IDENTIFIER ::= { iso(1) member-body(2)
    us(840) rsadsi(113549) encryptionAlgorithm(3) 7 }

rc2-cbc OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840)
    rsadsi(113549) encryptionAlgorithm(3) 2 }

hMAC-SHA1 OBJECT IDENTIFIER ::= { iso(1) identified-organization(3)
    dod(6) internet(1) security(5) mechanisms(5) 8 1 2 }


-- Algorithm Parameters

KeyWrapAlgorithm ::= AlgorithmIdentifier

RC2wrapParameter ::= RC2ParameterVersion

RC2ParameterVersion ::= INTEGER

CBCParameter ::= IV

IV ::= OCTET STRING  -- exactly 8 octets

Top      Up      ToC       Page 53 
RC2CBCParameter ::= SEQUENCE {
  rc2ParameterVersion INTEGER,
  iv OCTET STRING  }  -- exactly 8 octets


-- Content Type Object Identifiers

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

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


-- 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 }

Top      Up      ToC       Page 54 
-- Obsolete Extended Certificate syntax from PKCS#6

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

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

Signature ::= BIT STRING


END -- of CryptographicMessageSyntax

Top      Up      ToC       Page 55 
References

   3DES       American National Standards Institute.  ANSI X9.52-1998,
              Triple Data Encryption Algorithm Modes of Operation. 1998.

   DES        American National Standards Institute.  ANSI X3.106,
              "American National Standard for Information Systems - Data
              Link Encryption".  1983.

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

   DSS        National Institute of Standards and Technology.
              FIPS Pub 186: Digital Signature Standard.  19 May 1994.

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

   HMAC       Krawczyk, H., "HMAC: Keyed-Hashing for Message
              Authentication", RFC 2104, February 1997.

   MD5        Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
              April 1992.

   MODES      National Institute of Standards and Technology.
              FIPS Pub 81: DES Modes of Operation.  2 December 1980.

   MSG        Ramsdell, B., Editor, "S/MIME Version 3 Message
              Specification", RFC 2633, June 1999.

   NEWPKCS#1  Kaliski, B., "PKCS #1: RSA Encryption, Version 2.0",
              RFC 2347, October 1998.

   PROFILE    Housley, R., Ford, W., Polk, W. and D. Solo, "Internet
              X.509 Public Key Infrastructure: Certificate and CRL
              Profile", RFC 2459, January 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.

Top      Up      ToC       Page 56 
   RANDOM     Eastlake, D., Crocker, S. and J. Schiller, "Randomness
              Recommendations for Security", RFC 1750, December 1994.

   RC2        Rivest, R., "A Description of the RC2 (r) Encryption
              Algorithm", RFC 2268, March 1998.

   SHA1       National Institute of Standards and Technology.
              FIPS Pub 180-1: Secure Hash Standard.  17 April 1995.

   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.

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

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 messages 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.

Top      Up      ToC       Page 57 
   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
   a 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 1750 [RANDOM] offers important guidance in
   this area, and Appendix 3 of FIPS Pub 186 [DSS] provides one quality
   PRNG technique.

   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,
   a message content is encrypted with 168-bit Triple-DES and the
   Triple-DES content-encryption key is wrapped with a 40-bit RC2 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 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.

   Section 12.6 specifies key wrap algorithms used to encrypt a Triple-
   DES [3DES] content-encryption key with a Triple-DES key-encryption
   key or to encrypt a RC2 [RC2] content-encryption key with a RC2 key-
   encryption key.  The key wrap algorithms make use of CBC mode
   [MODES].  These key wrap algorithms have been reviewed for use with
   Triple and RC2.  They have not been reviewed for use with other
   cryptographic modes or other encryption algorithms.  Therefore, if a
   CMS implementation wishes to support ciphers in addition to Triple-
   DES or RC2, then additional key wrap algorithms need to be defined to
   support the additional ciphers.

   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 reduce.  Therefore, cryptographic
   algorithm implementations should be modular allowing new algorithms
   to be readily inserted.  That is, implementers should be prepared for
   the set of mandatory to implement algorithms to change over time.

   The countersignature unauthenticated attribute includes a digital
   signature that is computed on the content signature value, thus the
   countersigning process need not know the original signed content.

Top      Up      ToC       Page 58 
   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.

   Users of CMS, particularly those employing CMS to support interactive
   applications, should be aware that PKCS #1 Version 1.5 as specified
   in RFC 2313 [PKCS#1] is vulnerable to adaptive chosen ciphertext
   attacks when applied for encryption purposes.  Exploitation of this
   identified vulnerability, revealing the result of a particular RSA
   decryption, requires access to an oracle which will respond to a
   large number of ciphertexts (based on currently available results,
   hundreds of thousands or more), which are constructed adaptively in
   response to previously-received replies providing information on the
   successes or failures of attempted decryption operations.  As a
   result, the attack appears significantly less feasible to perpetrate
   for store-and-forward S/MIME environments than for directly
   interactive protocols.  Where CMS constructs are applied as an
   intermediate encryption layer within an interactive request-response
   communications environment, exploitation could be more feasible.

   An updated version of PKCS #1 has been published, PKCS #1 Version 2.0
   [NEWPKCS#1].  This new document will supersede RFC 2313.  PKCS #1
   Version 2.0 preserves support for the encryption padding format
   defined in PKCS #1 Version 1.5 [PKCS#1], and it also defines a new
   alternative.  To resolve the adaptive chosen ciphertext
   vulnerability, the PKCS #1 Version 2.0 specifies and recommends use
   of Optimal Asymmetric Encryption Padding (OAEP) when RSA encryption
   is used to provide confidentiality.  Designers of protocols and
   systems employing CMS for interactive environments should either
   consider usage of OAEP, or should ensure that information which could
   reveal the success or failure of attempted PKCS #1 Version 1.5
   decryption operations is not provided.  Support for OAEP will likely
   be added to a future version of the CMS specification.

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, 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, and Dave
   Solo for their efforts and support.

Top      Up      ToC       Page 59 
Author's Address

   Russell Housley
   SPYRUS
   381 Elden Street
   Suite 1120
   Herndon, VA 20170
   USA

   EMail: housley@spyrus.com

Top      Up      ToC       Page 60 
Full Copyright Statement

   Copyright (C) The Internet Society (1999).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.