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Network Working Group                                        R. HousleyRequest for Comments: 2630                                       SPYRUSCategory: Standards Track                                     June 1999Cryptographic Message SyntaxStatus of this Memo   This document specifies an Internet standards track protocol for the   Internet community, and requests discussion and suggestions for   improvements.  Please refer to the current edition of the "Internet   Official Protocol Standards" (STD 1) for the standardization state   and status of this protocol.  Distribution of this memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (1999).  All Rights Reserved.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   as specified inRFC 2315 [PKCS#7].  Wherever possible, backward   compatibility is preserved; however, changes were necessary to   accommodate attribute certificate transfer and key agreement   techniques for key management.Housley                     Standards Track                     [Page 1]

RFC 2630              Cryptographic Message Syntax             June 1999Table of Contents1   Introduction .................................................42   General Overview .............................................43   General Syntax ...............................................54   Data Content Type ............................................55   Signed-data Content Type .....................................65.1  SignedData Type .........................................75.2  EncapsulatedContentInfo Type ............................85.3  SignerInfo Type .........................................95.4  Message Digest Calculation Process ......................115.5  Message Signature Generation Process ....................125.6  Message Signature Verification Process ..................126   Enveloped-data Content Type ..................................126.1  EnvelopedData Type ......................................146.2  RecipientInfo Type ......................................156.2.1  KeyTransRecipientInfo Type .......................166.2.2  KeyAgreeRecipientInfo Type .......................176.2.3  KEKRecipientInfo Type ............................196.3  Content-encryption Process ..............................206.4  Key-encryption Process ..................................207   Digested-data Content Type ...................................218   Encrypted-data Content Type ..................................229   Authenticated-data Content Type ..............................239.1  AuthenticatedData Type ..................................239.2  MAC Generation ..........................................259.3  MAC Verification ........................................2610  Useful Types .................................................2710.1  Algorithm Identifier Types .............................2710.1.1  DigestAlgorithmIdentifier ......................2710.1.2  SignatureAlgorithmIdentifier ...................2710.1.3  KeyEncryptionAlgorithmIdentifier ...............2810.1.4  ContentEncryptionAlgorithmIdentifier ...........2810.1.5  MessageAuthenticationCodeAlgorithm .............2810.2  Other Useful Types .....................................2810.2.1  CertificateRevocationLists .....................2810.2.2  CertificateChoices .............................2910.2.3  CertificateSet .................................2910.2.4  IssuerAndSerialNumber ..........................3010.2.5  CMSVersion .....................................3010.2.6  UserKeyingMaterial .............................3010.2.7  OtherKeyAttribute ..............................30Housley                     Standards Track                     [Page 2]

RFC 2630              Cryptographic Message Syntax             June 199911  Useful Attributes ............................................3111.1  Content Type ...........................................3111.2  Message Digest .........................................3211.3  Signing Time ...........................................3211.4  Countersignature .......................................3412  Supported Algorithms .........................................3512.1  Digest Algorithms ......................................3512.1.1  SHA-1 ..........................................3512.1.2  MD5 ............................................3512.2  Signature Algorithms ...................................3612.2.1  DSA ............................................3612.2.2  RSA ............................................3612.3  Key Management Algorithms ..............................3612.3.1  Key Agreement Algorithms .......................36                     12.3.1.1  X9.42 Ephemeral-Static Diffie-Hellman. 3712.3.2  Key Transport Algorithms .......................3812.3.2.1  RSA ..................................3912.3.3  Symmetric Key-Encryption Key Algorithms ........3912.3.3.1  Triple-DES Key Wrap ..................4012.3.3.2  RC2 Key Wrap .........................4112.4  Content Encryption Algorithms ...........................4112.4.1  Triple-DES CBC ..................................4212.4.2  RC2 CBC .........................................4212.5  Message Authentication Code Algorithms ..................4212.5.1  HMAC with SHA-1 .................................4312.6  Triple-DES and RC2 Key Wrap Algorithms ..................4312.6.1  Key Checksum ....................................4412.6.2  Triple-DES Key Wrap .............................4412.6.3  Triple-DES Key Unwrap ...........................4412.6.4  RC2 Key Wrap ....................................4512.6.5  RC2 Key Unwrap ..................................46Appendix A:  ASN.1 Module ........................................47   References .......................................................55   Security Considerations ..........................................56   Acknowledgments ..................................................58   Author's Address .................................................59   Full Copyright Statement .........................................60Housley                     Standards Track                     [Page 3]

RFC 2630              Cryptographic Message Syntax             June 19991  Introduction   This document describes the Cryptographic Message Syntax.  This   syntax is used to digitally sign, digest, authenticate, or encrypt   arbitrary messages.   The Cryptographic Message Syntax describes an encapsulation syntax   for data protection.  It supports digital signatures, message   authentication codes, 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 signed 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   [X.208-88], using BER-encoding [X.209-88].  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 (CMS) is general enough to support   many different content types.  This document defines one protection   content, ContentInfo.  ContentInfo encapsulates a single identified   content type, and the identified type may provide further   encapsulation.  This document defines six content types: data,   signed-data, enveloped-data, digested-data, encrypted-data, and   authenticated-data.  Additional content types can be defined outside   this document.   An implementation that conforms to this specification must implement   the protection content, ContentInfo, and must implement the data,   signed-data, and enveloped-data content types.  The other content   types may be implemented if desired.   As a general design philosophy, each content type permits 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-Housley                     Standards Track                     [Page 4]

RFC 2630              Cryptographic Message Syntax             June 1999   pass operation has one significant drawback: it is difficult to   perform encode operations using the Distinguished Encoding Rules   (DER) [X.509-88] encoding in a single pass since the lengths of the   various components may not be known in advance.  However, signed   attributes within the signed-data content type and authenticated   attributes within the authenticated-data content type require DER   encoding.  Signed attributes and authenticated attributes must be   transmitted in DER form to ensure that recipients can verify a   content that contains one or more unrecognized attributes.  Signed   attributes and authenticated attributes are the only CMS data types   that require DER encoding.3  General Syntax   The Cryptographic Message Syntax (CMS) associates a content type   identifier with a 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 the associated 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 associated content.  The type of content can be      determined uniquely by contentType.  Content types for data,      signed-data, enveloped-data, digested-data, encrypted-data, and      authenticated-data are defined in this document.  If additional      content types are defined in other documents, the ASN.1 type      defined 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 structureHousley                     Standards Track                     [Page 5]

RFC 2630              Cryptographic Message Syntax             June 1999   (although they could have their own ASN.1 definition or other   structure).   The data content type is generally encapsulated in the signed-data,   enveloped-data, digested-data, encrypted-data, or authenticated-data   content type.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 the signer is signing any information other than the content,      the message digest of the content and the other information are      digested with the signer's message digest algorithm (seeSection5.4), 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 inSection 5.3.  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 inSection 5.1.   A recipient independently computes the message digest.  This message   digest and the signer's public key are used to verify the signature   value.  The signer's public key is referenced either by an issuer   distinguished name along with an issuer-specific serial number or by   a subject key identifier that uniquely identifies the certificate   containing the public key.  The signer's certificate may be included   in the SignedData certificates field.Housley                     Standards Track                     [Page 6]

RFC 2630              Cryptographic Message Syntax             June 1999   This section is divided into six parts.  The first part describes the   top-level type SignedData, the second part describes   EncapsulatedContentInfo, the third part describes the per-signer   information type SignerInfo, and the fourth, fifth, and sixth parts   describe the message digest calculation, signature generation, and   signature verification processes, respectively.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 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   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, the      encapsulated content type is id-data, and all of the elements of      SignerInfos are version 1, then the value of version shall be 1.      Alternatively, if attribute certificates are present, the      encapsulated content type is other than id-data, or any of the      elements of SignerInfos are version 3, 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 inSection 5.4.Housley                     Standards Track                     [Page 7]

RFC 2630              Cryptographic Message Syntax             June 1999      encapContentInfo is the signed content, consisting of a content      type identifier and the content itself.  Details of the      EncapsulatedContentInfo type are discussed insection 5.2.      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).  As discussed above, 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      details of the SignerInfo type are discussed insection 5.3.5.2  EncapsulatedContentInfo Type   The content is represented in the type EncapsulatedContentInfo:      EncapsulatedContentInfo ::= SEQUENCE {        eContentType ContentType,        eContent [0] EXPLICIT OCTET STRING OPTIONAL }      ContentType ::= OBJECT IDENTIFIER   The fields of type EncapsulatedContentInfo have the following   meanings:      eContentType is an object identifier that uniquely specifies the      content type.      eContent is the content itself, carried as an octet string.  The      eContent need not be DER encoded.Housley                     Standards Track                     [Page 8]

RFC 2630              Cryptographic Message Syntax             June 1999   The optional omission of the eContent within the   EncapsulatedContentInfo field makes it possible to construct   "external signatures."  In the case of external signatures, the   content being signed is absent from the EncapsulatedContentInfo value   included in the signed-data content type.  If the eContent value   within EncapsulatedContentInfo is absent, then the signatureValue is   calculated and the eContentType is assigned as though the eContent   value was present.   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 id-data (as defined insection 4), and the content   field of the EncapsulatedContentInfo value should be omitted.5.3  SignerInfo Type   Per-signer information is represented in the type SignerInfo:      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   The fields of type SignerInfo have the following meanings:      version is the syntax version number.  If the SignerIdentifier is      the CHOICE issuerAndSerialNumber, then the version shall be 1.  IfHousley                     Standards Track                     [Page 9]

RFC 2630              Cryptographic Message Syntax             June 1999      the SignerIdentifier is subjectKeyIdentifier, then the version      shall be 3.      sid specifies the signer's certificate (and thereby the signer's      public key).  The signer's public key is needed by the recipient      to verify the signature.  SignerIdentifier provides two      alternatives for specifying the signer's public key.  The      issuerAndSerialNumber alternative identifies the signer's      certificate by the issuer's distinguished name and the certificate      serial number; the subjectKeyIdentifier identifies the signer's      certificate by the X.509 subjectKeyIdentifier extension value.      digestAlgorithm identifies the message digest algorithm, and any      associated parameters, used by the signer.  The message digest is      computed on either the content being signed or the content      together with the signed attributes using the process described insection 5.4.  The message digest algorithm should be among those      listed in the digestAlgorithms field of the associated SignerData.      signedAttributes 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 id-data.      Each SignedAttribute in the SET must be DER encoded.  Useful      attribute types, such as signing time, are defined inSection 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.Section11.1 defines the content-type attribute.  The content-type         attribute is not required when used as part of a         countersignature unsigned attribute as defined insection 11.4.         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.      unsignedAttributes is a collection of attributes that are not      signed.  The field is optional.  Useful attribute types, such as      countersignatures, are defined inSection 11.Housley                     Standards Track                    [Page 10]

RFC 2630              Cryptographic Message Syntax             June 1999   The fields of type SignedAttribute and UnsignedAttribute have the   following meanings:      attrType indicates the type of attribute.  It is an object      identifier.      attrValues is a set of values that comprise the attribute.  The      type of each value in the set can be determined uniquely by      attrType.5.4  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   signed 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   encapContentInfo eContent OCTET STRING to which the signing process   is applied.  Only the octets comprising the value of the eContent   OCTET STRING are input to the message digest algorithm, not the tag   or the length octets.   The result of the message digest calculation process depends on   whether the signedAttributes 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   SignedAttributes value contained in the signedAttributes field.   Since the SignedAttributes value, when present, must contain the   content type and the content message digest attributes, those values   are indirectly included in the result.  The content type attribute is   not required when used as part of a countersignature unsigned   attribute as defined insection 11.4.  A separate encoding of the   signedAttributes field is performed for message digest calculation.   The IMPLICIT [0] tag in the signedAttributes 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 SignedAttributes value.   When the signedAttributes field is absent, then only the octets   comprising the value of the signedData encapContentInfo eContent   OCTET STRING (e.g., the contents of a file) are 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.Housley                     Standards Track                    [Page 11]

RFC 2630              Cryptographic Message Syntax             June 1999   Although the encapContentInfo eContent OCTET STRING tag and 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.5.5  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   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.5.6  Message Signature Verification Process   The input to the signature verification process includes the result   of the message digest calculation process and the signer's public   key.  The recipient may obtain the correct public key for the signer   by any means, but the preferred method is from a certificate obtained   from the SignedData certificates field.  The selection and validation   of the signer's public key may be based on certification path   validation (see [PROFILE]) as well as other external context, but is   beyond the scope of this document.  The details of the signature   verification 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   signedAttributes, then the content message digest must be calculated   as described insection 5.4.  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   signedAttributes 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 using any of the three key   management techniques for each recipient.Housley                     Standards Track                    [Page 12]

RFC 2630              Cryptographic Message Syntax             June 1999   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         symmetric key; and         symmetric key-encryption keys:  the content-encryption key is         encrypted in a previously distributed symmetric key-encryption         key.      3.  For each recipient, the encrypted content-encryption key and      other recipient-specific information are collected into a      RecipientInfo value, defined inSection 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; seeSection 6.3.      5.  The RecipientInfo values for all the recipients are collected      together with the encrypted content to form an EnvelopedData value      as defined inSection 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.Housley                     Standards Track                    [Page 13]

RFC 2630              Cryptographic Message Syntax             June 19996.1  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 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      UnprotectedAttributes ::= SET SIZE (1..MAX) OF Attribute   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 other than 0, then the version      shall be 2.  If unprotectedAttrs is present, then version shall be      2.  If originatorInfo is absent, all of the RecipientInfo      structures are version 0, and unprotectedAttrs is absent, 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 and CRLs:         certs is a collection of certificates.  certs may contain         originator certificates associated with several different keyHousley                     Standards Track                    [Page 14]

RFC 2630              Cryptographic Message Syntax             June 1999         management algorithms.  certs may also contain attribute         certificates associated with the originator.  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.      recipientInfos is a collection of per-recipient information.      There must be at least one element in the collection.      encryptedContentInfo is the encrypted content information.      unprotectedAttrs is a collection of attributes that are not      encrypted.  The field is optional.  Useful attribute types are      defined inSection 11.   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 inSection6.3.  The same content-encryption algorithm and content-encryption      key 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 has a different format for the three key managementHousley                     Standards Track                    [Page 15]

RFC 2630              Cryptographic Message Syntax             June 1999   techniques that are supported: key transport, key agreement, and   previously distributed symmetric key-encryption keys.  Any of the   three key management techniques can be used for each recipient of the   same encrypted content.  In all cases, the content-encryption key is   transferred to one or more recipient in encrypted form.      RecipientInfo ::= CHOICE {        ktri KeyTransRecipientInfo,        kari [1] KeyAgreeRecipientInfo,        kekri [2] KEKRecipientInfo }      EncryptedKey ::= OCTET STRING6.2.1  KeyTransRecipientInfo Type   Per-recipient information using key transport is represented in the   type KeyTransRecipientInfo.  Each instance of KeyTransRecipientInfo   transfers the content-encryption key to one recipient.      KeyTransRecipientInfo ::= SEQUENCE {        version CMSVersion,  -- always set to 0 or 2        rid RecipientIdentifier,        keyEncryptionAlgorithm KeyEncryptionAlgorithmIdentifier,        encryptedKey EncryptedKey }      RecipientIdentifier ::= CHOICE {        issuerAndSerialNumber IssuerAndSerialNumber,        subjectKeyIdentifier [0] SubjectKeyIdentifier }   The fields of type KeyTransRecipientInfo have the following meanings:      version is the syntax version number.  If the RecipientIdentifier      is the CHOICE issuerAndSerialNumber, then the version shall be 0.      If the RecipientIdentifier is subjectKeyIdentifier, 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.  The      RecipientIdentifier provides two alternatives for specifying the      recipient's certificate, and thereby the recipient's public key.      The recipient's certificate must contain a key transport public      key.  The content-encryption key is encrypted with the recipient's      public key.  The issuerAndSerialNumber alternative identifies the      recipient's certificate by the issuer's distinguished name and the      certificate serial number; the subjectKeyIdentifier identifies the      recipient's certificate by the X.509 subjectKeyIdentifier      extension value.Housley                     Standards Track                    [Page 16]

RFC 2630              Cryptographic Message Syntax             June 1999      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 inSection 6.4.      encryptedKey is the result of encrypting the content-encryption      key for the recipient.6.2.2  KeyAgreeRecipientInfo Type   Recipient information using key agreement is represented in the type   KeyAgreeRecipientInfo.  Each instance of KeyAgreeRecipientInfo will   transfer the content-encryption key to one or more recipient that   uses the same key agreement algorithm and domain parameters for that   algorithm.      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 }      RecipientKeyIdentifier ::= SEQUENCE {        subjectKeyIdentifier SubjectKeyIdentifier,        date GeneralizedTime OPTIONAL,        other OtherKeyAttribute OPTIONAL }      SubjectKeyIdentifier ::= OCTET STRINGHousley                     Standards Track                    [Page 17]

RFC 2630              Cryptographic Message Syntax             June 1999   The fields of type KeyAgreeRecipientInfo have the following meanings:      version is the syntax version number.  It shall always be 3.      originator is a CHOICE with three alternatives specifying the      sender's key agreement public key.  The sender uses the      corresponding private key and the recipient's public key to      generate a pairwise key.  The content-encryption key is encrypted      in the pairwise key.  The issuerAndSerialNumber alternative      identifies the sender's certificate, and thereby the sender's      public key, by the issuer's distinguished name and the certificate      serial number.  The subjectKeyIdentifier alternative identifies      the sender's certificate, and thereby the sender's public key, by      the X.509 subjectKeyIdentifier extension value.  The originatorKey      alternative includes the algorithm identifier and sender's key      agreement public key. Permitting originator anonymity since the      public key is not certified.      ukm is optional.  With some key agreement algorithms, the sender      provides a User Keying Material (UKM) to ensure that a different      key is generated each time the same two parties generate a      pairwise key.      keyEncryptionAlgorithm identifies the key-encryption algorithm,      and any associated parameters, used to encrypt the content-      encryption key in the key-encryption key.  The key-encryption      process is described inSection 6.4.      recipientEncryptedKeys includes a recipient identifier and      encrypted key for one or more recipients.  The      KeyAgreeRecipientIdentifier is a CHOICE with two alternatives      specifying the recipient's certificate, and thereby the      recipient's public key, that was used by the sender to generate a      pairwise key-encryption key.  The recipient's certificate must      contain a key agreement public key.  The content-encryption key is      encrypted in the pairwise key-encryption key.  The      issuerAndSerialNumber alternative identifies the recipient's      certificate by the issuer's distinguished name and the certificate      serial number; the RecipientKeyIdentifier is described below.  The      encryptedKey is the result of encrypting the content-encryption      key in the pairwise key-encryption key generated using the key      agreement algorithm.   The fields of type RecipientKeyIdentifier have the following   meanings:      subjectKeyIdentifier identifies the recipient's certificate by the      X.509 subjectKeyIdentifier extension value.Housley                     Standards Track                    [Page 18]

RFC 2630              Cryptographic Message Syntax             June 1999      date is optional.  When present, the date specifies which of the      recipient's previously distributed UKMs was used by the sender.      other is optional.  When present, this field contains additional      information used by the recipient to locate the public keying      material used by the sender.6.2.3  KEKRecipientInfo Type   Recipient information using previously distributed symmetric keys is   represented in the type KEKRecipientInfo.  Each instance of   KEKRecipientInfo will transfer the content-encryption key to one or   more recipients who have the previously distributed key-encryption   key.      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 }   The fields of type KEKRecipientInfo have the following meanings:      version is the syntax version number.  It shall always be 4.      kekid specifies a symmetric key-encryption key that was previously      distributed to the sender and one or more recipients.      keyEncryptionAlgorithm identifies the key-encryption algorithm,      and any associated parameters, used to encrypt the content-      encryption key with the key-encryption key.  The key-encryption      process is described inSection 6.4.      encryptedKey is the result of encrypting the content-encryption      key in the key-encryption key.   The fields of type KEKIdentifier have the following meanings:      keyIdentifier identifies the key-encryption key that was      previously distributed to the sender and one or more recipients.      date is optional.  When present, the date specifies a single key-      encryption key from a set that was previously distributed.Housley                     Standards Track                    [Page 19]

RFC 2630              Cryptographic Message Syntax             June 1999      other is optional.  When present, this field contains additional      information used by the recipient to determine the key-encryption      key used by the sender.6.3  Content-encryption Process   The content-encryption key for the desired content-encryption   algorithm is randomly generated.  The data to be protected is padded   as described below, then the padded data is encrypted using the   content-encryption key.  The encryption operation maps an arbitrary   string of octets (the data) to another string of octets (the   ciphertext) under control of a content-encryption key.  The encrypted   data is included in the envelopedData encryptedContentInfo   encryptedContent OCTET STRING.   The input to the content-encryption process is the "value" of the   content being enveloped.  Only the value octets of the envelopedData   encryptedContentInfo encryptedContent OCTET STRING are encrypted; the   OCTET STRING tag and length octets are not encrypted.   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-(lth mod k) octets all having value k-(lth mod k), where lth is   the length of the input.  In other words, the input is padded at   the trailing end with one of the following strings:                     01 -- if lth mod k = k-1                  02 02 -- if lth mod k = k-2                      .                      .                      .            k k ... k k -- if lth 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.   Any of the three key management techniques can be used for each   recipient of the same encrypted content.Housley                     Standards Track                    [Page 20]

RFC 2630              Cryptographic Message Syntax             June 19997  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 }   The digested-data content type shall have ASN.1 type DigestedData:      DigestedData ::= SEQUENCE {        version CMSVersion,        digestAlgorithm DigestAlgorithmIdentifier,        encapContentInfo EncapsulatedContentInfo,        digest Digest }      Digest ::= OCTET STRING   The fields of type DigestedData have the following meanings:      version is the syntax version number.  If the encapsulated content      type is id-data, then the value of version shall be 0; however, if      the encapsulated content type is other than id-data, then the      value of version shall be 2.      digestAlgorithm identifies the message digest algorithm, and any      associated parameters, under which the content is digested.  The      message-digesting process is the same as inSection 5.4 in the      case when there are no signed attributes.Housley                     Standards Track                    [Page 21]

RFC 2630              Cryptographic Message Syntax             June 1999      encapContentInfo is the content that is digested, as defined insection 5.2.      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 }   The encrypted-data content type shall have ASN.1 type EncryptedData:      EncryptedData ::= SEQUENCE {        version CMSVersion,        encryptedContentInfo EncryptedContentInfo,        unprotectedAttrs [1] IMPLICIT UnprotectedAttributes OPTIONAL }   The fields of type EncryptedData have the following meanings:      version is the syntax version number.  If unprotectedAttrs is      present, then version shall be 2.  If unprotectedAttrs is absent,      then version shall be 0.      encryptedContentInfo is the encrypted content information, as      defined inSection 6.1.      unprotectedAttrs is a collection of attributes that are not      encrypted.  The field is optional.  Useful attribute types are      defined inSection 11.Housley                     Standards Track                    [Page 22]

RFC 2630              Cryptographic Message Syntax             June 19999  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 verify the integrity of the content.  Any type of   content can be integrity protected for an arbitrary number of   recipients.   The process by which authenticated-data is constructed involves the   following steps:      1.  A message-authentication key for a particular message-      authentication algorithm is generated at random.      2.  The message-authentication key is encrypted for each      recipient.  The details of this encryption depend on the key      management algorithm used.      3.  For each recipient, the encrypted message-authentication key      and other recipient-specific information are collected into a      RecipientInfo value, defined inSection 6.2.      4.  Using the message-authentication key, the originator computes      a MAC value on the content.  If the originator is authenticating      any information in addition to the content (seeSection 9.2), a      message digest is calculated on the content, the message digest of      the content and the other information are authenticated using the      message-authentication key, and the result becomes the "MAC      value."9.1  AuthenticatedData Type   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 }Housley                     Standards Track                    [Page 23]

RFC 2630              Cryptographic Message Syntax             June 1999   The authenticated-data content type shall have ASN.1 type   AuthenticatedData:      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   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      originator.  It is present only if required by the key management      algorithm.  It may contain certificates, attribute certificates,      and CRLs, as defined inSection 6.1.      recipientInfos is a collection of per-recipient information, as      defined inSection 6.1.  There must be at least one element in the      collection.      macAlgorithm is a message authentication code (MAC) algorithm      identifier.  It identifies the MAC algorithm, along with any      associated parameters, used by the originator.  Placement of the      macAlgorithm field facilitates one-pass processing by the      recipient.      digestAlgorithm identifies the message digest algorithm, and any      associated parameters, used to compute a message digest on the      encapsulated content if authenticated attributes are present.  The      message digesting process is described inSection 9.2.  Placement      of the digestAlgorithm field facilitates one-pass processing by      the recipient.  If the digestAlgorithm field is present, then the      authenticatedAttributes field must also be present.Housley                     Standards Track                    [Page 24]

RFC 2630              Cryptographic Message Syntax             June 1999      encapContentInfo is the content that is authenticated, as defined      insection 5.2.      authenticatedAttributes is a collection of authenticated      attributes.  The authenticatedAttributes structure is optional,      but it must be present if the content type of the      EncapsulatedContentInfo value being authenticated is not id-data.      If the authenticatedAttributes field is present, then the      digestAlgorithm field must also be present.  Each      AuthenticatedAttribute in the SET must be DER encoded.  Useful      attribute types are defined inSection 11.  If the      authenticatedAttributes 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 authenticated.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.      mac is the message authentication code.      unauthenticatedAttributes is a collection of attributes that are      not authenticated.  The field is optional.  To date, no attributes      have been defined for use as unauthenticated attributes, but other      useful attribute types are defined inSection 11.9.2  MAC Generation   The MAC calculation process computes a message authentication code   (MAC) on either the message being authenticated or a message digest   of message being authenticated together with the originator's   authenticated attributes.   If authenticatedAttributes field is absent, the input to the MAC   calculation process is the value of the encapContentInfo eContent   OCTET STRING.  Only the octets comprising the value of the eContent   OCTET STRING are input to the MAC algorithm; the tag and the length   octets are omitted.  This has the advantage that the length of the   content being authenticated need not be known in advance of the MAC   generation process.   If authenticatedAttributes field is present, the content-type   attribute (as described inSection 11.1) and the message-digest   attribute (as described insection 11.2) must be included, and the   input to the MAC calculation process is the DER encoding ofHousley                     Standards Track                    [Page 25]

RFC 2630              Cryptographic Message Syntax             June 1999   authenticatedAttributes.  A separate encoding of the   authenticatedAttributes field is performed for message digest   calculation.  The IMPLICIT [2] 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 [2] tag, is to be included in the message digest   calculation along with the length and content octets of the   authenticatedAttributes value.   The message digest calculation process computes a message digest on   the content being authenticated.  The initial input to the message   digest calculation process is the "value" of the encapsulated content   being authenticated.  Specifically, the input is the encapContentInfo   eContent OCTET STRING to which the authentication process is applied.   Only the octets comprising the value of the encapContentInfo eContent   OCTET STRING are input to the message digest algorithm, not the tag   or the length octets.  This has the advantage that the length of the   content being authenticated need not be known in advance.  Although   the encapContentInfo eContent OCTET STRING tag and 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 input to the MAC calculation process includes the MAC input data,   defined above, and an authentication key conveyed in a recipientInfo   structure.  The details of MAC calculation depend on the MAC   algorithm employed (e.g., HMAC).  The object identifier, along with   any parameters, that specifies the MAC algorithm employed by the   originator is carried in the macAlgorithm field.  The MAC value   generated by the originator is encoded as an OCTET STRING and carried   in the mac field.9.3  MAC Verification   The input to the MAC verification process includes the input data   (determined based on the presence or absence of the   authenticatedAttributes field, as defined in 9.2), and the   authentication key conveyed in recipientInfo.  The details of the MAC   verification process depend on the MAC algorithm employed.   The recipient may not rely on any MAC values or message digest values   computed by the originator.  The content is authenticated as   described insection 9.2.  If the originator includes authenticated   attributes, then the content of the authenticatedAttributes is   authenticated as described insection 9.2.  For authentication to   succeed, the message MAC value calculated by the recipient must beHousley                     Standards Track                    [Page 26]

RFC 2630              Cryptographic Message Syntax             June 1999   the same as the value of the mac field.  Similarly, for   authentication to succeed when the authenticatedAttributes field is   present, the content message digest value calculated by the recipient   must be the same as the message digest value included in the   authenticatedAttributes message-digest attribute.10  Useful Types   This section is divided into two parts.  The first part defines   algorithm identifiers, and the second part defines other useful   types.10.1  Algorithm Identifier Types   All of the algorithm identifiers have the same type:   AlgorithmIdentifier.  The definition of AlgorithmIdentifier is   imported from X.509 [X.509-88].   There are many alternatives for each type of algorithm listed.  For   each of these five types,Section 12 lists the algorithms that must   be included in a CMS implementation.10.1.1  DigestAlgorithmIdentifier   The DigestAlgorithmIdentifier type identifies a message-digest   algorithm.  Examples include SHA-1, MD2, and MD5.  A message-digest   algorithm maps an octet string (the message) to another octet string   (the message digest).      DigestAlgorithmIdentifier ::= AlgorithmIdentifier10.1.2  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.      SignatureAlgorithmIdentifier ::= AlgorithmIdentifierHousley                     Standards Track                    [Page 27]

RFC 2630              Cryptographic Message Syntax             June 199910.1.3  KeyEncryptionAlgorithmIdentifier   The KeyEncryptionAlgorithmIdentifier type identifies a key-encryption   algorithm used to encrypt a content-encryption key.  The encryption   operation maps an octet string (the key) to another octet string (the   encrypted key) under control of a key-encryption key.  The decryption   operation is the inverse of the encryption operation.  Context   determines which operation is intended.   The details of encryption and decryption depend on the key management   algorithm used.  Key transport, key agreement, and previously   distributed symmetric key-encrypting keys are supported.      KeyEncryptionAlgorithmIdentifier ::= AlgorithmIdentifier10.1.4  ContentEncryptionAlgorithmIdentifier   The ContentEncryptionAlgorithmIdentifier type identifies a content-   encryption algorithm.  Examples include Triple-DES and RC2.  A   content-encryption algorithm supports encryption and decryption   operations.  The encryption operation maps an octet string (the   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.      ContentEncryptionAlgorithmIdentifier ::= AlgorithmIdentifier10.1.5  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.      MessageAuthenticationCodeAlgorithm ::= AlgorithmIdentifier10.2  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 andHousley                     Standards Track                    [Page 28]

RFC 2630              Cryptographic Message Syntax             June 1999   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 inRFC 2459 [PROFILE].   The definition of CertificateList is imported from X.509.      CertificateRevocationLists ::= SET OF CertificateList10.2.2  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 X9.5710.2.3  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.Housley                     Standards Track                    [Page 29]

RFC 2630              Cryptographic Message Syntax             June 1999      CertificateSet ::= SET OF CertificateChoices10.2.4  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 ::= INTEGER10.2.5  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 STRING10.2.7  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 }Housley                     Standards Track                    [Page 30]

RFC 2630              Cryptographic Message Syntax             June 199911  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] andRFC 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.Housley                     Standards Track                    [Page 31]

RFC 2630              Cryptographic Message Syntax             June 199911.2  Message Digest   The message-digest attribute type specifies the message digest of the   encapContentInfo eContent OCTET STRING being signed in signed-data   (seesection 5.4) or authenticated in authenticated-data (seesection9.2).  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.Housley                     Standards Track                    [Page 32]

RFC 2630              Cryptographic Message Syntax             June 1999   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,Housley                     Standards Track                    [Page 33]

RFC 2630              Cryptographic Message Syntax             June 1999   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.Housley                     Standards Track                    [Page 34]

RFC 2630              Cryptographic Message Syntax             June 199912  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 inRFC 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.Housley                     Standards Track                    [Page 35]

RFC 2630              Cryptographic Message Syntax             June 199912.2  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 inRFC 2347 [NEWPKCS#1].RFC2347 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-Housley                     Standards Track                    [Page 36]

RFC 2630              Cryptographic Message Syntax             June 1999   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 insection 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 inRFC 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:Housley                     Standards Track                    [Page 37]

RFC 2630              Cryptographic Message Syntax             June 1999         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 insection 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 encryptedKeyHousley                     Standards Track                    [Page 38]

RFC 2630              Cryptographic Message Syntax             June 1999   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   inRFC 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 inRFC 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 inRFC 2437   [NEWPKCS#1].  WithinRFC 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.Housley                     Standards Track                    [Page 39]

RFC 2630              Cryptographic Message Syntax             June 1999   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 insection 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.Housley                     Standards Track                    [Page 40]

RFC 2630              Cryptographic Message Syntax             June 199912.3.3.2  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 insection 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.Housley                     Standards Track                    [Page 41]

RFC 2630              Cryptographic Message Syntax             June 199912.4.1  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 octets12.4.2  RC2 CBC   The RC2 algorithm is described inRFC 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.Housley                     Standards Track                    [Page 42]

RFC 2630              Cryptographic Message Syntax             June 1999   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 inRFC 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 Sections12.6.2 and12.6.3.  CMS   implementations should include encryption of a RC2 content-encryption   key with a RC2 key-encryption key using the algorithm specified in   Sections12.6.4 and12.6.5.  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.Housley                     Standards Track                    [Page 43]

RFC 2630              Cryptographic Message Syntax             June 199912.6.1  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       inSection 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.Housley                     Standards Track                    [Page 44]

RFC 2630              Cryptographic Message Syntax             June 1999   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       inSection 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 inSection 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.Housley                     Standards Track                    [Page 45]

RFC 2630              Cryptographic Message Syntax             June 199912.6.5  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 inSection 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.Housley                     Standards Track                    [Page 46]

RFC 2630              Cryptographic Message Syntax             June 1999Appendix A:  ASN.1 ModuleCryptographicMessageSyntax    { 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 SyntaxContentInfo ::= SEQUENCE {  contentType ContentType,  content [0] EXPLICIT ANY DEFINED BY contentType }ContentType ::= OBJECT IDENTIFIERSignedData ::= SEQUENCE {  version CMSVersion,  digestAlgorithms DigestAlgorithmIdentifiers,  encapContentInfo EncapsulatedContentInfo,  certificates [0] IMPLICIT CertificateSet OPTIONAL,  crls [1] IMPLICIT CertificateRevocationLists OPTIONAL,  signerInfos SignerInfos }DigestAlgorithmIdentifiers ::= SET OF DigestAlgorithmIdentifierSignerInfos ::= SET OF SignerInfoHousley                     Standards Track                    [Page 47]

RFC 2630              Cryptographic Message Syntax             June 1999EncapsulatedContentInfo ::= 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 AttributeUnsignedAttributes ::= SET SIZE (1..MAX) OF AttributeAttribute ::= SEQUENCE {  attrType OBJECT IDENTIFIER,  attrValues SET OF AttributeValue }AttributeValue ::= ANYSignatureValue ::= OCTET STRINGEnvelopedData ::= 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 RecipientInfoEncryptedContentInfo ::= SEQUENCE {  contentType ContentType,  contentEncryptionAlgorithm ContentEncryptionAlgorithmIdentifier,  encryptedContent [0] IMPLICIT EncryptedContent OPTIONAL }EncryptedContent ::= OCTET STRINGHousley                     Standards Track                    [Page 48]

RFC 2630              Cryptographic Message Syntax             June 1999UnprotectedAttributes ::= SET SIZE (1..MAX) OF AttributeRecipientInfo ::= CHOICE {  ktri KeyTransRecipientInfo,  kari [1] KeyAgreeRecipientInfo,  kekri [2] KEKRecipientInfo }EncryptedKey ::= OCTET STRINGKeyTransRecipientInfo ::= 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 RecipientEncryptedKeyRecipientEncryptedKey ::= SEQUENCE {  rid KeyAgreeRecipientIdentifier,  encryptedKey EncryptedKey }KeyAgreeRecipientIdentifier ::= CHOICE {  issuerAndSerialNumber IssuerAndSerialNumber,  rKeyId [0] IMPLICIT RecipientKeyIdentifier }Housley                     Standards Track                    [Page 49]

RFC 2630              Cryptographic Message Syntax             June 1999RecipientKeyIdentifier ::= SEQUENCE {  subjectKeyIdentifier SubjectKeyIdentifier,  date GeneralizedTime OPTIONAL,  other OtherKeyAttribute OPTIONAL }SubjectKeyIdentifier ::= OCTET STRINGKEKRecipientInfo ::= 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 STRINGEncryptedData ::= 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 AttributeUnauthAttributes ::= SET SIZE (1..MAX) OF AttributeMessageAuthenticationCode ::= OCTET STRINGHousley                     Standards Track                    [Page 50]

RFC 2630              Cryptographic Message Syntax             June 1999DigestAlgorithmIdentifier ::= AlgorithmIdentifierSignatureAlgorithmIdentifier ::= AlgorithmIdentifierKeyEncryptionAlgorithmIdentifier ::= AlgorithmIdentifierContentEncryptionAlgorithmIdentifier ::= AlgorithmIdentifierMessageAuthenticationCodeAlgorithm ::= AlgorithmIdentifierCertificateRevocationLists ::= SET OF CertificateListCertificateChoices ::= CHOICE {  certificate Certificate,  -- See X.509  extendedCertificate [0] IMPLICIT ExtendedCertificate,  -- Obsolete  attrCert [1] IMPLICIT AttributeCertificate }  -- See X.509 & X9.57CertificateSet ::= SET OF CertificateChoicesIssuerAndSerialNumber ::= SEQUENCE {  issuer Name,  serialNumber CertificateSerialNumber }CMSVersion ::= INTEGER  { v0(0), v1(1), v2(2), v3(3), v4(4) }UserKeyingMaterial ::= OCTET STRINGOtherKeyAttribute ::= SEQUENCE {  keyAttrId OBJECT IDENTIFIER,  keyAttr ANY DEFINED BY keyAttrId OPTIONAL }-- CMS AttributesMessageDigest ::= OCTET STRINGSigningTime  ::= TimeTime ::= CHOICE {  utcTime UTCTime,  generalTime GeneralizedTime }Countersignature ::= SignerInfoHousley                     Standards Track                    [Page 51]

RFC 2630              Cryptographic Message Syntax             June 1999-- Algorithm Identifierssha-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 ParametersKeyWrapAlgorithm ::= AlgorithmIdentifierRC2wrapParameter ::= RC2ParameterVersionRC2ParameterVersion ::= INTEGERCBCParameter ::= IVIV ::= OCTET STRING  -- exactly 8 octetsHousley                     Standards Track                    [Page 52]

RFC 2630              Cryptographic Message Syntax             June 1999RC2CBCParameter ::= SEQUENCE {  rc2ParameterVersion INTEGER,  iv OCTET STRING  }  -- exactly 8 octets-- Content Type Object Identifiersid-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 Identifiersid-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 }Housley                     Standards Track                    [Page 53]

RFC 2630              Cryptographic Message Syntax             June 1999-- Obsolete Extended Certificate syntax from PKCS#6ExtendedCertificate ::= SEQUENCE {  extendedCertificateInfo ExtendedCertificateInfo,  signatureAlgorithm SignatureAlgorithmIdentifier,  signature Signature }ExtendedCertificateInfo ::= SEQUENCE {  version CMSVersion,  certificate Certificate,  attributes UnauthAttributes }Signature ::= BIT STRINGEND -- of CryptographicMessageSyntaxHousley                     Standards Track                    [Page 54]

RFC 2630              Cryptographic Message Syntax             June 1999References   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.Housley                     Standards Track                    [Page 55]

RFC 2630              Cryptographic Message Syntax             June 1999   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.Housley                     Standards Track                    [Page 56]

RFC 2630              Cryptographic Message Syntax             June 1999   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.Housley                     Standards Track                    [Page 57]

RFC 2630              Cryptographic Message Syntax             June 1999   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   inRFC 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 supersedeRFC 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.Housley                     Standards Track                    [Page 58]

RFC 2630              Cryptographic Message Syntax             June 1999Author's Address   Russell Housley   SPYRUS   381 Elden Street   Suite 1120   Herndon, VA 20170   USA   EMail: housley@spyrus.comHousley                     Standards Track                    [Page 59]

RFC 2630              Cryptographic Message Syntax             June 1999Full 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.Housley                     Standards Track                    [Page 60]