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S/MIME Working Group                                         R. Housley
Internet Draft                                                   SPYRUS
expires in six months                                      January 1998


                      Cryptographic Message Syntax

                     <draft-ietf-smime-cms-03.txt>


Status of this Memo

   This document is an Internet-Draft.  Internet-Drafts are working
   documents of the Internet Engineering Task Force (IETF), its areas,
   and its working groups.  Note that other groups may also distribute
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Abstract

   This document describes the Cryptographic Message Syntax.  This
   syntax is used to digitally sign, digest, authenticate, or encrypt
   arbitrary messages.

   The Cryptographic Message Syntax is derived from PKCS #7 version 1.5.
   Wherever possible, backward compatibility is preserved; however,
   changes were necessary to accommodate attribute certificate transfer
   and key agreement techniques for key management.

   This draft is being discussed on the "ietf-smime" mailing list.  To
   join the list, send a message to <ietf-smime-request@imc.org> with
   the single word "subscribe" in the body of the message.  Also, there
   is a Web site for the mailing list at <http://www.imc.org/ietf-
   smime/>.






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1  Introduction

   This document describes the Cryptographic Message Syntax.  This
   syntax is used to digitally sign or encrypt arbitrary messages.

   The Cryptographic Message Syntax describes an encapsulation syntax
   for data protection.  It supports digital signatures and encryption.
   The syntax allows multiple encapsulation, so one encapsulation
   envelope can be nested inside another.  Likewise, one party can
   digitally sign some previously encapsulated data.  It also allows
   arbitrary attributes, such as signing time, to be authenticated along
   with the message content, and provides for other attributes such as
   countersignatures to be associated with a signature.

   The Cryptographic Message Syntax can support a variety of
   architectures for certificate-based key management, such as the one
   defined by the PKIX working group.

   The Cryptographic Message Syntax values are generated using ASN.1,
   using BER-encoding.  Values are typically represented as octet
   strings.  While many systems are capable of transmitting arbitrary
   octet strings reliably, it is well known that many electronic-mail
   systems are not.  This document does not address mechanisms for
   encoding octet strings for reliable transmission in such
   environments.

2  General Overview

   The Cryptographic Message Syntax is general enough to support many
   different content types.  This document defines six content types:
   data, signed-data, enveloped-data, digested-data, encrypted-data, and
   authenticated-data.  Also, additional content types can be defined
   outside this document.

   An implementation that conforms to this specification must implement
   the data, signed-data, and enveloped-data content types.  The other
   content types may be implemented if desired.

   The Cryptographic Message Syntax exports one content type,
   ContentInfo, as well as the various object identifiers.

   As a general design philosophy, content types permit single pass
   processing using indefinite-length Basic Encoding Rules (BER)
   encoding.  Single-pass operation is especially helpful if content is
   large, stored on tapes, or is "piped" from another process.  Single-
   pass operation has one significant drawback: it is difficult to
   perform encode operations using the Distinguished Encoding Rules
   (DER) encoding in a single pass since the lengths of the various



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   components may not be known in advance.  Since the signed-data
   content type requires DER encoding, an extra pass may be necessary
   when a content type other than data is encapsulated.

3  General Syntax

   The Cryptographic Message Syntax associates a protection content type
   with a protection content.  The syntax shall have ASN.1 type
   ContentInfo:

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

      ContentType ::= OBJECT IDENTIFIER

   The fields of ContentInfo have the following meanings:

      contentType indicates the type of protection content.  It is an
      object identifier; it is a unique string of integers assigned by
      an authority that defines the content type.

      content is the protection content.  The type of protection content
      can be determined uniquely by contentType.  Protection content
      types for signed-data, enveloped-data, digested-data, encrypted-
      data, and authenticated-data are defined in this document.  If
      additional protection content types are defined in other
      documents, the ASN.1 type defined along with the object identifier
      should not be a CHOICE type.

4  Data Content Type

   The following object identifier identifies the data content type:

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

   The data content type is intended to refer to arbitrary octet
   strings, such as ASCII text files; the interpretation is left to the
   application.  Such strings need not have any internal structure
   (although they could have their own ASN.1 definition or other
   structure).

   The data content type is generally used in conjunction with the
   signed-data, enveloped-data, digested-data, encrypted-data, and
   authenticated-data protection content types.  The data content type
   is encapsulated in one of these protection content types.




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5  Signed-data Content Type

   The signed-data content type consists of a content of any type and
   zero or more signature values.  Any number of signers in parallel can
   sign any type of content.

   The typical application of the signed-data content type represents
   one signer's digital signature on content of the data content type.
   Another typical application disseminates certificates and certificate
   revocation lists (CRLs).

   The process by which signed-data is constructed involves the
   following steps:

      1.  For each signer, a message digest, or hash value, is computed
      on the content with a signer-specific message-digest algorithm.
      If two signers employ the same message digest algorithm, then the
      message digest need be computed for only one of them.  If the
      signer is authenticating any information other than the content
      (see Section 5.2), the message digest of the content and the other
      information are digested with the signer's message digest
      algorithm, and the result becomes the "message digest."

      2.  For each signer, the message digest is digitally signed using
      the signer's private key.

      3.  For each signer, the signature value and other signer-specific
      information are collected into a SignerInfo value, as defined in
      Section 5.2.  Certificates and CRLs for each signer, and those not
      corresponding to any signer, are collected in this step.

      4.  The message digest algorithms for all the signers and the
      SignerInfo values for all the signers are collected together with
      the content into a SignedData value, as defined in Section 5.1.

   A recipient independently computes the message digest.  This message
   digest and the signer's public key are used to validate the signature
   value.  The signer's public key is referenced by an issuer
   distinguished name and an issuer-specific serial number that uniquely
   identify the certificate containing the public key.  The signer's
   certificate may be included in the SignedData certificates field.

   This section is divided into five parts.  The first part describes
   the top-level type SignedData, the second part describes the per-
   signer information type SignerInfo, and the third, fourth, and fifth
   parts describe the message digest calculation, signature generation,
   and signature validation processes, respectively.




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5.1  SignedData Type

   The following object identifier identifies the signed-data content
   type:

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

   The signed-data content type shall have ASN.1 type SignedData:

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

      DigestAlgorithmIdentifiers ::= SET OF DigestAlgorithmIdentifier

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

      ContentType ::= OBJECT IDENTIFIER

      SignerInfos ::= SET OF SignerInfo

   The fields of type SignedData have the following meanings:

      version is the syntax version number.  If no attribute
      certificates are present in the certificates field, then the value
      of version shall be 1; however, if attribute certificates are
      present, then the value of version shall be 3.

      digestAlgorithms is a collection of message digest algorithm
      identifiers.  There may be any number of elements in the
      collection, including zero.  Each element identifies the message
      digest algorithm, along with any associated parameters, used by
      one or more signer.  The collection is intended to list the
      message digest algorithms employed by all of the signers, in any
      order, to facilitate one-pass signature verification.  The message
      digesting process is described in Section 5.3.

      encapContentInfo is the content that is signed.  It is a sequence
      of a content type identifier and the content itself.  An object
      identifier uniquely specifies the content type.  The content
      itself is carried in an octet string.



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      certificates is a collection of certificates.  It is intended that
      the set of certificates be sufficient to contain chains from a
      recognized "root" or "top-level certification authority" to all of
      the signers in the signerInfos field.  There may be more
      certificates than necessary, and there may be certificates
      sufficient to contain chains from two or more independent top-
      level certification authorities.  There may also be fewer
      certificates than necessary, if it is expected that recipients
      have an alternate means of obtaining necessary certificates (e.g.,
      from a previous set of certificates).  If no attribute
      certificates are present in the collection, then the value of
      version shall be 1; however, if attribute certificates are
      present, then the value of version shall be 3.

      crls is a collection of certificate revocation lists (CRLs).  It
      is intended that the set contain information sufficient to
      determine whether or not the certificates in the certificates
      field are valid, but such correspondence is not necessary.  There
      may be more CRLs than necessary, and there may also be fewer CRLs
      than necessary.

      signerInfos is a collection of per-signer information.  There may
      be any number of elements in the collection, including zero.

   The optional omission of the encapContentInfo field makes it possible
   to construct "external signatures."  In the case of external
   signatures, the content being signed would be absent from the
   EncapsulatedContentInfo value included in the signed-data content
   type.  If the EncapsulatedContentInfo value is absent, the
   signatureValue is calculated as though the EncapsulatedContentInfo
   value was present.  The presumed EncapsulatedContentInfo must have
   the content type set to id-data (as defined in section 4) and the
   content omitted.

   In the degenerate case where there are no signers, the
   EncapsulatedContentInfo value being "signed" is irrelevant.  In this
   case, the content type within the EncapsulatedContentInfo value being
   "signed" should be data (as defined in section 4), and the content
   field of the EncapsulatedContentInfo value should be omitted.












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5.2  SignerInfo Type

   Per-signer information is represented in the type SignerInfo:

      SignerInfo ::= SEQUENCE {
        version Version,
        issuerAndSerialNumber IssuerAndSerialNumber,
        digestAlgorithm DigestAlgorithmIdentifier,
        authenticatedAttributes [0] IMPLICIT CMSAttributes OPTIONAL,
        signatureAlgorithm SignatureAlgorithmIdentifier,
        signature SignatureValue,
        unauthenticatedAttributes [1] IMPLICIT CMSAttributes OPTIONAL }

      CMSAttributes ::= SET OF CMSAttribute

      CMSAttribute ::= SEQUENCE {
        cmsAttrType OBJECT IDENTIFIER,
        critical BOOLEAN DEFAULT FALSE,
        cmsAttrValues SET OF CMSAttributeValue }

      CMSAttributeValue ::= ANY

      SignatureValue ::= OCTET STRING

   The fields of type SignerInfo have the following meanings:

      version is the syntax version number.  If any of the authenticated
      attributes, are critical, then the version shall be 3.  If all of
      the authenticated attributes are non-critical, then the version
      shall be 1.  If the authenticatedAttributes and field is absent,
      then version shall be 1.

      issuerAndSerialNumber specifies the signer's certificate (and
      thereby the signer's public key) by issuer distinguished name and
      issuer-specific serial number.

      digestAlgorithm identifies the message digest algorithm, and any
      associated parameters, used by the signer.  The message digest is
      computed over the encapsulated content and authenticated
      attributes, if present.  The message digest algorithm should be
      among those listed in the digestAlgorithms field of the associated
      SignerInfo value.  The message digesting process is described in
      Section 5.3.

      authenticatedAttributes is a collection of attributes that are
      signed.  The field is optional, but it must be present if the
      content type of the EncapsulatedContentInfo value being signed is
      not data.  The field may include critical and non-critical



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      attributes.  Useful attribute types, such as signing time, are
      defined in Section 11.  If the field is present, it must contain,
      at a minimum, the following two attributes:

         A content-type attribute having as its value the content type
         of the EncapsulatedContentInfo value being signed.  Section
         11.1 defines the content-type attribute.

         A message-digest attribute, having as its value the message
         digest of the content.  Section 11.2 defines the message-digest
         attribute.

      signatureAlgorithm identifies the signature algorithm, and any
      associated parameters, used by the signer to generate the digital
      signature.

      signature is the result of digital signature generation, using the
      message digest and the signer's private key.

      unauthenticatedAttributes is a collection of attributes that are
      not signed.  The field is optional, and it may not include
      critical attributes.  Useful attribute types, such as
      countersignatures, are defined in Section 11.

   The fields of type CMSAttribute have the following meanings:

      cmsAttrType indicates the type of attribute.  It is an object
      identifier.

      critical is a boolean value.  TRUE indicates that the attribute is
      critical, and FALSE indicates that the attribute is non-critical.
      A recipient must reject the signed-data if it encounters a
      critical attribute that it does not recognize; however, an
      unrecognized non-critical attribute may be ignored.

      cmsAttrValues is a set of values that comprise the attribute.  The
      type each value in the set can be determined uniquely by
      attributeType.

5.3  Message Digest Calculation Process

   The message digest calculation process computes a message digest on
   either the content being signed or the content together with the
   signer's authenticated attributes.  In either case, the initial input
   to the message digest calculation process is the "value" of the
   encapsulated content being signed.  Specifically, the initial input
   is the content OCTET STRING of the content field of the
   EncapsulatedContentInfo value to which the signing process is



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   applied.  Only the contents of the OCTET STRING are input to the
   message digest algorithm, not the identifier octets or the length
   octets.

   The result of the message digest calculation process depends on
   whether the authenticatedAttributes field is present.  When the field
   is absent, the result is just the message digest of the content as
   described above.  When the field is present, however, the result is
   the message digest of the complete DER encoding of the Attributes
   value contained in the authenticatedAttributes field.  Since the
   Attributes value, when present, must contain as attributes the
   content type and the content message digest, those values are
   indirectly included in the result.  A separate encoding of the
   authenticatedAttributes field is performed for message digest
   calculation.  The IMPLICIT [0] tag in the authenticatedAttributes
   field is not used for the DER encoding, rather an EXPLICIT SET OF tag
   is used.  That is, the DER encoding of the SET OF tag, rather than of
   the IMPLICIT [0] tag, is to be included in the message digest
   calculation along with the length and content octets of the
   CMSAttributes value.

   When the content being signed has a content type of data (as defined
   in section 4) and the authenticatedAttributes field is absent, then
   just the value of the data (e.g., the contents of a file) is input to
   the message digest calculation.  This has the advantage that the
   length of the content being signed need not be known in advance of
   the signature generation process.

   Although the identifier octets and the length octets are not included
   in the message digest calculation, they are still protected by other
   means.  The length octets are protected by the nature of the message
   digest algorithm since it is computationally infeasible to find any
   two distinct messages of any length that have the same message
   digest.

   The fact that the message digest is computed on part of a DER
   encoding does not mean that DER is the required method of
   representing that part for data transfer.  Indeed, it is expected
   that some implementations will store objects in forms other than
   their DER encodings, but such practices do not affect message digest
   computation.

5.4  Message Signature Generation Process

   The input to the signature generation process includes the result of
   the message digest calculation process and the signer's private key.
   The details of the signature generation depend on the signature
   algorithm employed.  The object identifier, along with any



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   parameters, that specifies the signature algorithm employed by the
   signer is carried in the signatureAlgorithm field.  The signature
   value generated by the signer is encoded as an OCTET STRING and
   carried in the signature field.

5.5  Message Signature Validation Process

   The input to the signature validation process includes the result of
   the message digest calculation process and the signer's public key.
   The details of the signature validation depend on the signature
   algorithm employed.

   The recipient may not rely on any message digest values computed by
   the originator.  If the signedData signerInfo includes
   authenticatedAttributes, then content message digest must be
   calculated as described in section 5.3.  For the signature to be
   valid, the message digest value calculated by the recipient must be
   the same as the value of the messageDigest attribute included in the
   authenticatedAttributes of the signedData signerInfo.

6  Enveloped-data Content Type

   The enveloped-data content type consists of an encrypted content of
   any type and encrypted content-encryption keys for one or more
   recipients.  The combination of the encrypted content and one
   encrypted content-encryption key for a recipient is a "digital
   envelope" for that recipient.  Any type of content can be enveloped
   for an arbitrary number of recipients.

   The typical application of the enveloped-data content type will
   represent one or more recipients' digital envelopes on content of the
   data or signed-data content types.

   Enveloped-data is constructed by the following steps:

      1.  A content-encryption key for a particular content-encryption
      algorithm is generated at random.

      2.  The content-encryption key is encrypted for each recipient.
      The details of this encryption depend on the key management
      algorithm used, but three general techniques are supported:

         key transport:  the content-encryption key is encrypted in the
         recipient's public key;

         key agreement:  the recipient's public key and the sender's
         private key are used to generate a pairwise symmetric key, then
         the content-encryption key is encrypted in the pairwise



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         symmetric key; and

         mail list keys:  the content-encryption key is encrypted in a
         previously distributed symmetric key.

      3.  For each recipient, the encrypted content-encryption key and
      other recipient-specific information are collected into a
      RecipientInfo value, defined in Section 6.2.

      4.  The content is encrypted with the content-encryption key.
      Content encryption may require that the content be padded to a
      multiple of some block size; see Section 6.3.

      5.  The RecipientInfo values for all the recipients are collected
      together with the encrypted content to form an EnvelopedData value
      as defined in Section 6.1.

   A recipient opens the digital envelope by decrypting one of the
   encrypted content-encryption keys and then decrypting the encrypted
   content with the recovered content-encryption key.

   This section is divided into four parts.  The first part describes
   the top-level type EnvelopedData, the second part describes the per-
   recipient information type RecipientInfo, and the third and fourth
   parts describe the content-encryption and key-encryption processes.

6.1  EnvelopedData Type

   The following object identifier identifies the enveloped-data content
   type:

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

   The enveloped-data content type shall have ASN.1 type EnvelopedData:

      EnvelopedData ::= SEQUENCE {
        version Version,
        originatorInfo [0] IMPLICIT OriginatorInfo OPTIONAL,
        recipientInfos RecipientInfos,
        encryptedContentInfo EncryptedContentInfo }

      OriginatorInfo ::= SEQUENCE {
        certs [0] IMPLICIT CertificateSet OPTIONAL,
        crls [1] IMPLICIT CertificateRevocationLists OPTIONAL,
        ukms [2] IMPLICIT UserKeyingMaterials OPTIONAL }

      RecipientInfos ::= SET OF RecipientInfo



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

      EncryptedContent ::= OCTET STRING

   The fields of type EnvelopedData have the following meanings:

      version is the syntax version number.  If originatorInfo is
      present, then version shall be 2.  If any of the RecipientInfo
      structures included have a version of 2, then the version shall be
      2.  If originatorInfo is absent and all of the RecipientInfo
      structures are version 0, then version shall be 0.

      originatorInfo optionally provides information about the
      originator.  It is present only if required by the key management
      algorithm.  It may contain certificates, CRLs, and user keying
      material (UKMs):

         certs is a collection of certificates.  certs may contain
         originator certificates associated with several different key
         management algorithms.  The certificates contained in certs are
         intended to be sufficient to make chains from a recognized
         "root" or "top-level certification authority" to all
         recipients.  However, certs may contain more certificates than
         necessary, and there may be certificates sufficient to make
         chains from two or more independent top-level certification
         authorities.  Alternatively, certs may contain fewer
         certificates than necessary, if it is expected that recipients
         have an alternate means of obtaining necessary certificates
         (e.g., from a previous set of certificates).

         crls is a collection of CRLs.  It is intended that the set
         contain information sufficient to determine whether or not the
         certificates in the certs field are valid, but such
         correspondence is not necessary.  There may be more CRLs than
         necessary, and there may also be fewer CRLs than necessary.

         ukms is a collection of UKMs.  The set includes a UKM for each
         key management algorithm employed by the originator that
         requires one.  In general, several recipients will use each UKM
         in the set.

      recipientInfos is a collection of per-recipient information.
      There must be at least one element in the collection.

      encryptedContentInfo is the encrypted content information.



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   The fields of type EncryptedContentInfo have the following meanings:

      contentType indicates the type of content.

      contentEncryptionAlgorithm identifies the content-encryption
      algorithm, and any associated parameters, used to encrypt the
      content.  The content-encryption process is described in Section
      6.3.  The same algorithm is used for all recipients.

      encryptedContent is the result of encrypting the content.  The
      field is optional, and if the field is not present, its intended
      value must be supplied by other means.

   The recipientInfos field comes before the encryptedContentInfo field
   so that an EnvelopedData value may be processed in a single pass.

6.2  RecipientInfo Type

   Per-recipient information is represented in the type RecipientInfo:

      RecipientInfo ::= SEQUENCE {
        version Version,
        rid RecipientIdentifier,
        originatorCert [0] EXPLICIT EntityIdentifier OPTIONAL,
        keyEncryptionAlgorithm KeyEncryptionAlgorithmIdentifier,
        encryptedKey EncryptedKey }

      RecipientIdentifier ::= CHOICE {
        issuerAndSerialNumber IssuerAndSerialNumber,
        rKeyId [0] IMPLICIT RecipientKeyIdentifier,
        mlKeyId [1] IMPLICIT MailListKeyIdentifier }

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

      MailListKeyIdentifier ::= SEQUENCE {
        kekIdentifier OCTET STRING,
        date GeneralizedTime OPTIONAL,
        other OtherKeyAttribute OPTIONAL }

      EntityIdentifier ::= CHOICE {
        issuerAndSerialNumber IssuerAndSerialNumber,
        subjectKeyIdentifier SubjectKeyIdentifier }

      SubjectKeyIdentifier ::= OCTET STRING




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      EncryptedKey ::= OCTET STRING

   The fields of type RecipientInfo have the following meanings:

      version is the syntax version number.  If the OriginatorCert is
      absent and the RecipientIdentifier is the CHOICE
      issuerAndSerialNumber, then the version shall be 0.  If the
      OriginatorCert is present or the RecipientIdentifier is either the
      CHOICE rKeyId or mlKeyId, then the version shall be 2.

      rid specifies the recipient's certificate or key that was used by
      the sender to protect the content-encryption key.

      originatorCert optionally specifies the originator's certificate
      to be used by this recipient.  This field should be included when
      the originator has more than one certificate containing a public
      key associated with the key management algorithm used for this
      recipient.

      keyEncryptionAlgorithm identifies the key-encryption algorithm,
      and any associated parameters, used to encrypt the content-
      encryption key for the recipient.  The key-encryption process is
      described in Section 6.4.

      encryptedKey is the result of encrypting the content-encryption
      key for the recipient.

   The RecipientIdentifier is a CHOICE with three alternatives.  The
   first two alternatives, issuerAndSerialNumber and rKeyId, specifies
   the recipient's certificate, and thereby the recipient's public key.
   The rKeyId alternative may optionally specify other parameters
   needed, such as the date.  If the recipient's certificate contains a
   key transport public key, then the content-encryption key is
   encrypted with the recipient's public key.  If the recipient's
   certificate contains a key agreement public key, then a pairwise
   symmetric key is established and used to encrypt the content-
   encryption key.  The third alternative, mlKeyId, specifies a
   symmetric key encryption key that was previously distributed to the
   sender and recipient.

   The fields of type RecipientKeyIdentifier have the following
   meanings:

      subjectKeyIdentifier identifies the recipient's certificate by the
      X.509 subjectKeyIdentifier extension value.

      date is optional.  When present, the date specifies which of the
      recipient's UKMs was used by the sender.



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      other is optional.  When present, this field contains additional
      information used by the recipient to locate the keying material
      used by the sender.

   The fields of type MailListKeyIdentifier have the following meanings:

      kekIdentifier identifies the key-encryption key that was
      previously distributed to the sender and the recipient.

      date is optional.  When present, the date specifies a single key-
      encryption key from a set that was previously distributed to the
      sender and the recipient.

      other is optional.  When present, this field contains additional
      information used by the recipient to locate the keying material
      used by the sender.

6.3  Content-encryption Process

   The input to the content-encryption process is the "value" of the
   content being enveloped.  Only the content octets; identifier or
   length octets are not included.

   When the content being enveloped has content type of data (as defined
   in section 4), then just the value of the data (e.g., the contents of
   a file) is encrypted.  This has the advantage that the length of the
   content being encrypted need not be known in advance of the
   encryption process.

   The identifier octets and the length octets are not encrypted.  The
   length octets may be protected implicitly by the encryption process,
   depending on the encryption algorithm.  The identifier octets are not
   protected at all, although they can be recovered from the content
   type, assuming that the content type uniquely determines the
   identifier octets.  Explicit protection of the identifier and length
   octets requires that the signed-data content type be employed prior
   to digital enveloping.

   Some content-encryption algorithms assume the input length is a
   multiple of k octets, where k is greater than one.  For such
   algorithms, the input shall be padded at the trailing end with
   k-(l mod k) octets all having value k-(l mod k), where l is the
   length of the input.  In other words, the input is padded at the








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   trailing end with one of the following strings:

                     01 -- if l mod k = k-1
                  02 02 -- if l mod k = k-2
                      .
                      .
                      .
            k k ... k k -- if l mod k = 0

   The padding can be removed unambiguously since all input is padded,
   including input values that are already a multiple of the block size,
   and no padding string is a suffix of another.  This padding method is
   well defined if and only if k is less than 256.

6.4  Key-encryption Process

   The input to the key-encryption process -- the value supplied to the
   recipient's key-encryption algorithm --is just the "value" of the
   content-encryption key.

7  Digested-data Content Type

   The digested-data content type consists of content of any type and a
   message digest of the content.

   Typically, the digested-data content type is used to provide content
   integrity, and the result generally becomes an input to the
   enveloped-data content type.

   The following steps construct digested-data:

      1.  A message digest is computed on the content with a message-
      digest algorithm.

      2.  The message-digest algorithm and the message digest are
      collected together with the content into a DigestedData value.

   A recipient verifies the message digest by comparing the message
   digest to an independently computed message digest.

   The following object identifier identifies the digested-data content
   type:

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






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   The digested-data content type shall have ASN.1 type DigestedData:

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

      Digest ::= OCTET STRING

   The fields of type DigestedData have the following meanings:

      version is the syntax version number.  It shall be 0.

      digestAlgorithm identifies the message digest algorithm, and any
      associated parameters, under which the content is digested.  The
      message-digesting process is the same as in Section 5.3 in the
      case when there are no authenticated attributes.

      encapContentInfo is the content that is digested, as defined in
      section 5.1.

      digest is the result of the message-digesting process.

   The ordering of the digestAlgorithm field, the encapContentInfo
   field, and the digest field makes it possible to process a
   DigestedData value in a single pass.

8  Encrypted-data Content Type

   The encrypted-data content type consists of encrypted content of any
   type.  Unlike the enveloped-data content type, the encrypted-data
   content type has neither recipients nor encrypted content-encryption
   keys.  Keys must be managed by other means.

   The typical application of the encrypted-data content type will be to
   encrypt the content of the data content type for local storage,
   perhaps where the encryption key is a password.

   The following object identifier identifies the encrypted-data content
   type:

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







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   The encrypted-data content type shall have ASN.1 type EncryptedData:

      EncryptedData ::= SEQUENCE {
        version Version,
        encryptedContentInfo EncryptedContentInfo }

   The fields of type EncryptedData have the following meanings:

      version is the syntax version number.  It shall be 0.

      encryptedContentInfo is the encrypted content information, as
      defined in Section 6.1.

9  Authenticated-data Content Type

   The authenticated-data content type consists of content of any type,
   a message authentication code (MAC), and encrypted authentication
   keys for one or more recipients.  The combination of the MAC and one
   encrypted authentication key for a recipient is necessary for that
   recipient to validate the integrity of the content.  Any type of
   content can be integrity protected for an arbitrary number of
   recipients.

   The following object identifier identifies the authenticated-data
   content type:

      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 authenticated-data content type shall have ASN.1 type
   AuthenticatedData:

      AuthenticatedData ::= SEQUENCE {
        version Version,
        originatorInfo [0] IMPLICIT OriginatorInfo OPTIONAL,
        recipientInfos RecipientInfos,
        macAlgorithm MessageAuthenticationCodeAlgorithm,
        encapContentInfo EncapsulatedContentInfo,
        mac MessageAuthenticationCode }

      MessageAuthenticationCode ::= OCTET STRING

   The fields of type AuthenticatedData have the following meanings:

      version is the syntax version number.  It shall be 0.

      originatorInfo optionally provides information about the



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      originator.  It is present only if required by the key management
      algorithm.  It may contain certificates, CRLs, and user keying
      material (UKMs), as defined in Section 6.1.

      recipientInfos is a collection of per-recipient information, as
      defined in Section 6.1.  There must be at least one element in the
      collection.

      macAlgorithm is a message authentication code algorithm
      identifier.  It identifies the message authentication code
      algorithm, along with any associated parameters, used by the
      originator.  Placement of the macAlgorithm field facilitates one-
      pass processing by the recipient.

      encapContentInfo is the content that is authenticated, as defined
      in section 5.1.

      mac is the message authentication code.

10  Useful Types

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

10.1  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 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 definition of CertificateList is imported from X.509.

      CertificateRevocationLists ::= SET OF CertificateList

10.2  ContentEncryptionAlgorithmIdentifier

   The ContentEncryptionAlgorithmIdentifier type identifies a content-
   encryption algorithm such as DES.  A content-encryption algorithm
   supports encryption and decryption operations.  The encryption
   operation maps an octet string (the message) 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.





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   The definition of AlgorithmIdentifier is imported from X.509.

      ContentEncryptionAlgorithmIdentifier ::= AlgorithmIdentifier

10.3  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 message) to another octet string
   (the message digest).

   The definition of AlgorithmIdentifier is imported from X.509.

      DigestAlgorithmIdentifier ::= AlgorithmIdentifier

10.4  SignatureAlgorithmIdentifier

   The SignatureAlgorithmIdentifier type identifies a signature
   algorithm.  Examples include DSS and RSA.  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.

   The definition of AlgorithmIdentifier is imported from X.509.

      SignatureAlgorithmIdentifier ::= AlgorithmIdentifier

10.5  CertificateChoices

   The CertificateChoices type gives either a PKCS #6 extended
   certificate, an X.509 certificate, or an X.509 attribute certificate.
   The PKCS #6 extended certificate is obsolete.  It is included for
   backward compatibility, and its use should be avoided.

   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







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10.6  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.

      CertificateSet ::= SET OF CertificateChoices

10.7  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, and the definition of
   SerialNumber is imported from X.509.

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

      SerialNumber ::= INTEGER

10.8  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, and previously
   distributed symmetric key-encrypting keys are supported.

   The definition of AlgorithmIdentifier is imported from X.509.

      KeyEncryptionAlgorithmIdentifier ::= AlgorithmIdentifier




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10.9  Version

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

      Version ::= INTEGER

10.10  UserKeyingMaterial

   The UserKeyingMaterial type gives a syntax user keying material
   (UKM).  Some key management algorithms require UKMs.  The sender
   provides a UKM for the specific key management algorithm.  The UKM is
   employed by all of the recipients that use the same key encryption
   algorithm.

      UserKeyingMaterial ::= SEQUENCE {
        keyEncryptionAlgorithm KeyEncryptionAlgorithmIdentifier,
        ukm OCTET STRING }

10.11  UserKeyingMaterials

   The UserKeyingMaterial type provides a set of user keying materials
   (UKMs).  This allows the sender to provide a UKM for each key
   management algorithm that requires one.

      UserKeyingMaterials ::= SET OF UserKeyingMaterial

10.12  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 }

10.13  MessageAuthenticationCodeAlgorithm

   The MessageAuthenticationCodeAlgorithm type identifies a message
   authentication code (MAC) algorithm.  Examples include DES MAC and
   HMAC.  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.





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   The definition of AlgorithmIdentifier is imported from X.509.

      MessageAuthenticationCodeAlgorithm ::= AlgorithmIdentifier

11  Useful Attributes

   This section defines attributes that may used with signed-data.  All
   of these attributes were originally defined in PKCS #9, and they are
   included here for easy reference.  The attributes are not listed in
   any particular order.

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 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.

11.2  Message Digest

   The message-digest attribute type specifies the message digest of the
   contents octets of the DER encoding of the content field of the
   ContentInfo value being signed in signed-data, where the message
   digest is computed using the signer's message digest algorithm.  The
   message-digest attribute type is required if there are any
   authenticated attributes present.

   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



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   A message-digest attribute must have a single attribute value.

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 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.

   Dates through the year 2049 must be encoded as UTCTime, and dates in
   the year 2050 or later must be encoded as GeneralizedTime.

   A signing-time attribute must have a single attribute value.

   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 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
   unauthenticated attribute; it cannot be an authenticated attribute.








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   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 authenticatedAttributes 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 fact that a countersignature is computed on a signature value
   means that the countersigning process need not know the original
   content input to the signing process.  This has advantages both in
   efficiency and in confidentiality.  A countersignature, since it has
   type SignerInfo, can itself contain a countersignature attribute.
   Thus it is possible to construct arbitrarily long series of
   countersignatures.

12  Supported Algorithms

   To be supplied.  However, this section will list the must implement
   algorithms and other algorithms that may be implemented.  It will
   include:

   MUST implement: DSS, SHA-1, Diffie-Hellman (X9.42), and Triple-DES
   CBC (with three keys).

   MAY implement: RSA (signature and key management), MD5, RC2 (40 bit),
   DES CBC, and DES MAC.








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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

   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 OPTIONAL }

   ContentType ::= OBJECT IDENTIFIER

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

   DigestAlgorithmIdentifiers ::= SET OF DigestAlgorithmIdentifier

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

   SignerInfos ::= SET OF SignerInfo




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   SignerInfo ::= SEQUENCE {
     version Version,
     issuerAndSerialNumber IssuerAndSerialNumber,
     digestAlgorithm DigestAlgorithmIdentifier,
     authenticatedAttributes [0] IMPLICIT CMSAttributes OPTIONAL,
     signatureAlgorithm SignatureAlgorithmIdentifier,
     signature SignatureValue,
     unauthenticatedAttributes [1] IMPLICIT CMSAttributes OPTIONAL }

   CMSAttributes ::= SET OF CMSAttribute

   CMSAttribute ::= SEQUENCE {
     cmsAttrType OBJECT IDENTIFIER,
     critical BOOLEAN DEFAULT FALSE,
     cmsAttrValues SET OF CMSAttributeValue }

   CMSAttributeValue ::= ANY

   SignatureValue ::= OCTET STRING

   EnvelopedData ::= SEQUENCE {
     version Version,
     originatorInfo [0] IMPLICIT OriginatorInfo OPTIONAL,
     recipientInfos RecipientInfos,
     encryptedContentInfo EncryptedContentInfo }

   OriginatorInfo ::= SEQUENCE {
     certs [0] IMPLICIT CertificateSet OPTIONAL,
     crls [1] IMPLICIT CertificateRevocationLists OPTIONAL,
     ukms [2] IMPLICIT UserKeyingMaterials OPTIONAL }

   RecipientInfos ::= SET OF RecipientInfo

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

   EncryptedContent ::= OCTET STRING

   RecipientInfo ::= SEQUENCE {
     version Version,
     rid RecipientIdentifier,
     originatorCert [0] EXPLICIT EntityIdentifier OPTIONAL,
     keyEncryptionAlgorithm KeyEncryptionAlgorithmIdentifier,
     encryptedKey EncryptedKey }





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   RecipientIdentifier ::= CHOICE {
     issuerAndSerialNumber IssuerAndSerialNumber,
     rKeyId [0] IMPLICIT RecipientKeyIdentifier,
     mlKeyId [1] IMPLICIT MailListKeyIdentifier }

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

   MailListKeyIdentifier ::= SEQUENCE {
     kekIdentifier OCTET STRING,
     date GeneralizedTime OPTIONAL,
     other OtherKeyAttribute OPTIONAL }

   EntityIdentifier ::= CHOICE {
     issuerAndSerialNumber IssuerAndSerialNumber,
     subjectKeyIdentifier SubjectKeyIdentifier }

   SubjectKeyIdentifier ::= OCTET STRING

   EncryptedKey ::= OCTET STRING

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

   Digest ::= OCTET STRING

   EncryptedData ::= SEQUENCE {
     version Version,
     encryptedContentInfo EncryptedContentInfo }

   AuthenticatedData ::= SEQUENCE {
     version Version,
     originatorInfo [0] IMPLICIT OriginatorInfo OPTIONAL,
     recipientInfos RecipientInfos,
     macAlgorithm MessageAuthenticationCodeAlgorithm,
     encapContentInfo EncapsulatedContentInfo,
     mac MessageAuthenticationCode }

   MessageAuthenticationCode ::= OCTET STRING

   CertificateRevocationLists ::= SET OF CertificateList

   ContentEncryptionAlgorithmIdentifier ::= AlgorithmIdentifier



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   DigestAlgorithmIdentifier ::= AlgorithmIdentifier

   SignatureAlgorithmIdentifier ::= AlgorithmIdentifier

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

   CertificateSet ::= SET OF CertificateChoices

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

   SerialNumber ::= INTEGER

   KeyEncryptionAlgorithmIdentifier ::= AlgorithmIdentifier

   Version ::= INTEGER

   UserKeyingMaterial ::= SEQUENCE {
     algorithm AlgorithmIdentifier,
     ukm OCTET STRING }

   UserKeyingMaterials ::= SET OF UserKeyingMaterial

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

   MessageAuthenticationCodeAlgorithm ::= AlgorithmIdentifier



   -- CMS Attributes

   MessageDigest ::= OCTET STRING

   SigningTime  ::= Time

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

   Countersignature ::= SignerInfo





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   -- Object Identifiers

   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 }

   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 }



















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   -- 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 Version,
     certificate Certificate,
     attributes Attributes }

   Signature ::= BIT STRING


   END -- of CryptographicMessageSyntax































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References

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

   PKCS #7    RSA Laboratories.  PKCS #7: Cryptographic Message Syntax
              Standard.  Version 1.5, November 1993.

              PKCS #7: Cryptographic Message Syntax, Internet Draft
              draft-hoffman-pkcs-crypt-msg-xx.

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

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

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

   X.501      CCITT.  Recommendation X.501: The Directory - Models.  1988.

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

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 and the
   content-encryption key.  Compromise of the key management private 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 encrypted content.

Author Address

   Russell Housley
   SPYRUS
   PO Box 1198
   Herndon, VA 20172
   USA
   housley@spyrus.com



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