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diff --git a/doc/rfc/rfc3852.txt b/doc/rfc/rfc3852.txt new file mode 100644 index 0000000..cd3f6cb --- /dev/null +++ b/doc/rfc/rfc3852.txt @@ -0,0 +1,3139 @@ + + + + + + +Network Working Group R. Housley +Request for Comments: 3852 Vigil Security +Obsoletes: 3369 July 2004 +Category: Standards Track + + + Cryptographic Message Syntax (CMS) + +Status 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 (2004). + +Abstract + + This document describes the Cryptographic Message Syntax (CMS). This + syntax is used to digitally sign, digest, authenticate, or encrypt + arbitrary message content. + +Table of Contents + + 1. Introduction. . . . . . . . . . . . . . . . . . . . . . . . . 3 + 1.1. Evolution of the CMS . . . . . . . . . . . . . . . . . 3 + 1.1.1. Changes Since PKCS #7 Version 1.5. . . . . . . 3 + 1.1.2. Changes Since RFC 2630 . . . . . . . . . . . . 4 + 1.1.3. Changes Since RFC 3369 . . . . . . . . . . . . 4 + 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . 5 + 1.3. Version Numbers . . . . . . . . . . . . . . . . . . . . 5 + 2. General Overview. . . . . . . . . . . . . . . . . . . . . . . 5 + 3. General Syntax . . . . . . . . . . . . . . . . . . . . . . . 6 + 4. Data Content Type . . . . . . . . . . . . . . . . . . . . . . 6 + 5. Signed-data Content Type. . . . . . . . . . . . . . . . . . . 7 + 5.1. SignedData Type. . . . . . . . . . . . . . . . . . . . 8 + 5.2. EncapsulatedContentInfo Type . . . . . . . . . . . . . 10 + 5.2.1. Compatibility with PKCS #7. . . . . . . . . . 11 + 5.3. SignerInfo Type. . . . . . . . . . . . . . . . . . . . 12 + 5.4. Message Digest Calculation Process . . . . . . . . . . 14 + 5.5. Signature Generation Process . . . . . . . . . . . . . 15 + 5.6. Signature Verification Process . . . . . . . . . . . . 15 + 6. Enveloped-data Content Type . . . . . . . . . . . . . . . . . 16 + 6.1. EnvelopedData Type . . . . . . . . . . . . . . . . . . 17 + + + +Housley Standards Track [Page 1] + +RFC 3852 Cryptographic Message Syntax July 2004 + + + 6.2. RecipientInfo Type . . . . . . . . . . . . . . . . . . 19 + 6.2.1. KeyTransRecipientInfo Type. . . . . . . . . . 20 + 6.2.2. KeyAgreeRecipientInfo Type. . . . . . . . . . 21 + 6.2.3. KEKRecipientInfo Type . . . . . . . . . . . . 24 + 6.2.4. PasswordRecipientInfo Type. . . . . . . . . . 25 + 6.2.5. OtherRecipientInfo Type . . . . . . . . . . . 26 + 6.3. Content-encryption Process . . . . . . . . . . . . . . 26 + 6.4. Key-encryption Process . . . . . . . . . . . . . . . . 27 + 7. Digested-data Content Type. . . . . . . . . . . . . . . . . . 27 + 8. Encrypted-data Content Type . . . . . . . . . . . . . . . . . 28 + 9. Authenticated-data Content Type . . . . . . . . . . . . . . . 29 + 9.1. AuthenticatedData Type . . . . . . . . . . . . . . . . 30 + 9.2. MAC Generation . . . . . . . . . . . . . . . . . . . . 32 + 9.3. MAC Verification . . . . . . . . . . . . . . . . . . . 33 + 10. Useful Types. . . . . . . . . . . . . . . . . . . . . . . . . 33 + 10.1. Algorithm Identifier Types . . . . . . . . . . . . . . 33 + 10.1.1. DigestAlgorithmIdentifier . . . . . . . . . . 34 + 10.1.2. SignatureAlgorithmIdentifier. . . . . . . . . 34 + 10.1.3. KeyEncryptionAlgorithmIdentifier. . . . . . . 34 + 10.1.4. ContentEncryptionAlgorithmIdentifier. . . . . 34 + 10.1.5. MessageAuthenticationCodeAlgorithm. . . . . . 35 + 10.1.6. KeyDerivationAlgorithmIdentifier. . . . . . . 35 + 10.2. Other Useful Types . . . . . . . . . . . . . . . . . . 35 + 10.2.1. RevocationInfoChoices . . . . . . . . . . . . 35 + 10.2.2. CertificateChoices. . . . . . . . . . . . . . 36 + 10.2.3. CertificateSet. . . . . . . . . . . . . . . . 37 + 10.2.4. IssuerAndSerialNumber . . . . . . . . . . . . 37 + 10.2.5. CMSVersion. . . . . . . . . . . . . . . . . . 38 + 10.2.6. UserKeyingMaterial. . . . . . . . . . . . . . 38 + 10.2.7. OtherKeyAttribute . . . . . . . . . . . . . . 38 + 11. Useful Attributes . . . . . . . . . . . . . . . . . . . . . . 38 + 11.1. Content Type . . . . . . . . . . . . . . . . . . . . . 39 + 11.2. Message Digest . . . . . . . . . . . . . . . . . . . . 39 + 11.3. Signing Time . . . . . . . . . . . . . . . . . . . . . 40 + 11.4. Countersignature . . . . . . . . . . . . . . . . . . . 41 + 12. ASN.1 Modules . . . . . . . . . . . . . . . . . . . . . . . . 42 + 12.1. CMS ASN.1 Module . . . . . . . . . . . . . . . . . . . 43 + 12.2. Version 1 Attribute Certificate ASN.1 Module . . . . . 50 + 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 51 + 13.1. Normative References . . . . . . . . . . . . . . . . . 51 + 13.2. Informative References . . . . . . . . . . . . . . . . 52 + 14. Security Considerations . . . . . . . . . . . . . . . . . . . 53 + 15. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 55 + 16. Author's Address. . . . . . . . . . . . . . . . . . . . . . . 55 + 17. Full Copyright Statement. . . . . . . . . . . . . . . . . . . 56 + + + + + + +Housley Standards Track [Page 2] + +RFC 3852 Cryptographic Message Syntax July 2004 + + +1. Introduction + + This document describes the Cryptographic Message Syntax (CMS). This + syntax is used to digitally sign, digest, authenticate, or encrypt + arbitrary message content. + + The CMS describes an encapsulation syntax for data protection. It + supports digital signatures and encryption. The syntax allows + multiple encapsulations; 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 CMS can support a variety of architectures for certificate-based + key management, such as the one defined by the PKIX working group + [PROFILE]. + + The CMS 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. + +1.1. Evolution of the CMS + + The CMS is derived from PKCS #7 version 1.5, which is documented in + RFC 2315 [PKCS#7]. PKCS #7 version 1.5 was developed outside of the + IETF; it was originally published as an RSA Laboratories Technical + Note in November 1993. Since that time, the IETF has taken + responsibility for the development and maintenance of the CMS. + Today, several important IETF standards-track protocols make use of + the CMS. + + This section describes the changes that the IETF has made to the CMS + in each of the published versions. + +1.1.1. Changes Since PKCS #7 Version 1.5 + + RFC 2630 [CMS1] was the first version of the CMS on the IETF + standards track. Wherever possible, backward compatibility with PKCS + #7 version 1.5 is preserved; however, changes were made to + accommodate version 1 attribute certificate transfer and to support + algorithm independent key management. PKCS #7 version 1.5 included + + + + +Housley Standards Track [Page 3] + +RFC 3852 Cryptographic Message Syntax July 2004 + + + support only for key transport. RFC 2630 adds support for key + agreement and previously distributed symmetric key-encryption key + techniques. + +1.1.2. Changes Since RFC 2630 + + RFC 3369 [CMS2] obsoletes RFC 2630 [CMS1] and RFC 3211 [PWRI]. + Password-based key management is included in the CMS specification, + and an extension mechanism to support new key management schemes + without further changes to the CMS is specified. Backward + compatibility with RFC 2630 and RFC 3211 is preserved; however, + version 2 attribute certificate transfer is added, and the use of + version 1 attribute certificates is deprecated. + + S/MIME v2 signatures [OLDMSG], which are based on PKCS#7 version 1.5, + are compatible with S/MIME v3 signatures [MSG], which are based on + RFC 2630. However, there are some subtle compatibility issues with + signatures based on PKCS #7 version 1.5. These issues are discussed + in section 5.2.1. These issues remain with the current version of + the CMS. + + Specific cryptographic algorithms are not discussed in this document, + but they were discussed in RFC 2630. The discussion of specific + cryptographic algorithms has been moved to a separate document + [CMSALG]. Separation of the protocol and algorithm specifications + allows the IETF to update each document independently. This + specification does not require the implementation of any particular + algorithms. Rather, protocols that rely on the CMS are expected to + choose appropriate algorithms for their environment. The algorithms + may be selected from [CMSALG] or elsewhere. + +1.1.3. Changes Since RFC 3369 + + This document obsoletes RFC 3369 [CMS2]. As discussed in the + previous section, RFC 3369 introduced an extension mechanism to + support new key management schemes without further changes to the + CMS. This document introduces a similar extension mechanism to + support additional certificate formats and revocation status + information formats without further changes to the CMS. These + extensions are primarily documented in section 10.2.1 and section + 10.2.2. Backward compatibility with earlier versions of the CMS is + preserved. + + The use of version numbers is described in section 1.3. + + Since the publication of RFC 3369, a few errata have been noted. + These errata are posted on the RFC Editor web site. These errors + have been corrected in this document. + + + +Housley Standards Track [Page 4] + +RFC 3852 Cryptographic Message Syntax July 2004 + + + The text in section 11.4 that describes the counter signature + unsigned attribute is clarified. Hopefully the revised text is + clearer about the portion of the SignerInfo signature that is covered + by a countersignature. + +1.2. Terminology + + In this document, the key words MUST, MUST NOT, REQUIRED, SHOULD, + SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL are to be interpreted as + described in [STDWORDS]. + +1.3. Version Numbers + + Each of the major data structures includes a version number as the + first item in the data structure. The version numbers are intended + to avoid ASN.1 decode errors. Some implementations do not check the + version number prior to attempting a decode, and if a decode error + occurs, then the version number is checked as part of the error + handling routine. This is a reasonable approach; it places error + processing outside of the fast path. This approach is also forgiving + when an incorrect version number is used by the sender. + + Most of the initial version numbers were assigned in PKCS #7 version + 1.5. Others were assigned when the structure was initially created. + Whenever a structure is updated, a higher version number is assigned. + However, to ensure maximum interoperability the higher version number + is only used when the new syntax feature is employed. That is, the + lowest version number that supports the generated syntax is used. + +2. General Overview + + The 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. + + 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 5] + +RFC 3852 Cryptographic Message Syntax July 2004 + + + 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 need to 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 data types used + in the CMS that require DER encoding. + +3. General Syntax + + The following object identifier identifies the content information + type: + + id-ct-contentInfo OBJECT IDENTIFIER ::= { iso(1) member-body(2) + us(840) rsadsi(113549) pkcs(1) pkcs9(9) smime(16) ct(1) 6 } + + The CMS associates a content type identifier with a content. The + syntax MUST 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 } + + + + +Housley Standards Track [Page 6] + +RFC 3852 Cryptographic Message Syntax July 2004 + + + The data content type is intended to refer to arbitrary octet + strings, such as ASCII text files; the interpretation is left to the + application. Such strings need not have any internal structure + (although they could have their own ASN.1 definition or other + structure). + + S/MIME uses id-data to identify MIME encoded content. The use of + this content identifier is specified in RFC 2311 for S/MIME v2 + [OLDMSG] and RFC 3851 for S/MIME v3.1 [MSG]. + + 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 (see Section 5.4), 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 + in Section 5.3. Certificates and CRLs for each signer, and + those not corresponding to any signer, are collected in this + step. + + + + + + + +Housley Standards Track [Page 7] + +RFC 3852 Cryptographic Message Syntax July 2004 + + + 4. The message digest algorithms for all the signers and the + SignerInfo values for all the signers are collected together + with the content into a SignedData value, as defined in Section + 5.1. + + A recipient independently computes the message digest. This message + digest and the signer's public key are used to 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 can be included + in the SignedData certificates field. + + 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 RevocationInfoChoices 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. The appropriate value + depends on certificates, eContentType, and SignerInfo. The + version MUST be assigned as follows: + + + + +Housley Standards Track [Page 8] + +RFC 3852 Cryptographic Message Syntax July 2004 + + + IF ((certificates is present) AND + (any certificates with a type of other are present)) OR + ((crls is present) AND + (any crls with a type of other are present)) + THEN version MUST be 5 + ELSE + IF (certificates is present) AND + (any version 2 attribute certificates are present) + THEN version MUST be 4 + ELSE + IF ((certificates is present) AND + (any version 1 attribute certificates are present)) OR + (any SignerInfo structures are version 3) OR + (encapContentInfo eContentType is other than id-data) + THEN version MUST be 3 + ELSE version MUST be 1 + + 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. + Implementations MAY fail to validate signatures that use a digest + algorithm that is not included in this set. The message digesting + process is described in Section 5.4. + + encapContentInfo is the signed content, consisting of a content + type identifier and the content itself. Details of the + EncapsulatedContentInfo type are discussed in section 5.2. + + certificates is a collection of certificates. It is intended that + the set of certificates be sufficient to contain certification + paths 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 certification paths 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). The + signer's certificate MAY be included. The use of version 1 + attribute certificates is strongly discouraged. + + crls is a collection of revocation status information. It is + intended that the collection contain information sufficient to + determine whether the certificates in the certificates field are + + + +Housley Standards Track [Page 9] + +RFC 3852 Cryptographic Message Syntax July 2004 + + + valid, but such correspondence is not necessary. Certificate + revocation lists (CRLs) are the primary source of revocation + status information. 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 in section 5.3. + Since each signer can employ a digital signature technique and + future specifications could update the syntax, all implementations + MUST gracefully handle unimplemented versions of SignerInfo. + Further, since all implementations will not support every possible + signature algorithm, all implementations MUST gracefully handle + unimplemented signature algorithms when they are encountered. + +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. The object identifier + uniquely specifies the content type. + + eContent is the content itself, carried as an octet string. The + eContent need not be DER encoded. + + 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" MUST be id-data (as defined in section 4), and the content + field of the EncapsulatedContentInfo value MUST be omitted. + + + + +Housley Standards Track [Page 10] + +RFC 3852 Cryptographic Message Syntax July 2004 + + +5.2.1. Compatibility with PKCS #7 + + This section contains a word of warning to implementers that wish to + support both the CMS and PKCS #7 [PKCS#7] SignedData content types. + + Both the CMS and PKCS #7 identify the type of the encapsulated + content with an object identifier, but the ASN.1 type of the content + itself is variable in PKCS #7 SignedData content type. + + PKCS #7 defines content as: + + content [0] EXPLICIT ANY DEFINED BY contentType OPTIONAL + + The CMS defines eContent as: + + eContent [0] EXPLICIT OCTET STRING OPTIONAL + + The CMS definition is much easier to use in most applications, and it + is compatible with both S/MIME v2 and S/MIME v3. S/MIME signed + messages using the CMS and PKCS #7 are compatible because identical + signed message formats are specified in RFC 2311 for S/MIME v2 + [OLDMSG] and RFC 3851 for S/MIME v3.1 [MSG]. S/MIME v2 encapsulates + the MIME content in a Data type (that is, an OCTET STRING) carried in + the SignedData contentInfo content ANY field, and S/MIME v3 carries + the MIME content in the SignedData encapContentInfo eContent OCTET + STRING. Therefore, in both S/MIME v2 and S/MIME v3, the MIME content + is placed in an OCTET STRING and the message digest is computed over + the identical portions of the content. That is, the message digest + is computed over the octets comprising the value of the OCTET STRING, + neither the tag nor length octets are included. + + There are incompatibilities between the CMS and PKCS #7 SignedData + types when the encapsulated content is not formatted using the Data + type. For example, when an RFC 2634 [ESS] signed receipt is + encapsulated in the CMS SignedData type, then the Receipt SEQUENCE is + encoded in the SignedData encapContentInfo eContent OCTET STRING and + the message digest is computed using the entire Receipt SEQUENCE + encoding (including tag, length and value octets). However, if an + RFC 2634 signed receipt is encapsulated in the PKCS #7 SignedData + type, then the Receipt SEQUENCE is DER encoded [X.509-88] in the + SignedData contentInfo content ANY field (a SEQUENCE, not an OCTET + STRING). Therefore, the message digest is computed using only the + value octets of the Receipt SEQUENCE encoding. + + The following strategy can be used to achieve backward compatibility + with PKCS #7 when processing SignedData content types. If the + implementation is unable to ASN.1 decode the SignedData type using + the CMS SignedData encapContentInfo eContent OCTET STRING syntax, + + + +Housley Standards Track [Page 11] + +RFC 3852 Cryptographic Message Syntax July 2004 + + + then the implementation MAY attempt to decode the SignedData type + using the PKCS #7 SignedData contentInfo content ANY syntax and + compute the message digest accordingly. + + The following strategy can be used to achieve backward compatibility + with PKCS #7 when creating a SignedData content type in which the + encapsulated content is not formatted using the Data type. + Implementations MAY examine the value of the eContentType, and then + adjust the expected DER encoding of eContent based on the object + identifier value. For example, to support Microsoft Authenticode + [MSAC], the following information MAY be included: + + eContentType Object Identifier is set to { 1 3 6 1 4 1 311 2 1 4 } + + eContent contains DER encoded Authenticode signing information + +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 + + + + + + + +Housley Standards Track [Page 12] + +RFC 3852 Cryptographic Message Syntax July 2004 + + + 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 MUST be 1. If + the SignerIdentifier is subjectKeyIdentifier, then the version + MUST 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 a key identifier. When an X.509 certificate is + reference, the key identifier matches the X.509 + subjectKeyIdentifier extension value. When other certificate + formats are referenced, the documents that specify the certificate + format and their use with the CMS must include details on matching + the key identifier to the appropriate certificate field. + Implementations MUST support the reception of the + issuerAndSerialNumber and subjectKeyIdentifier forms of + SignerIdentifier. When generating a SignerIdentifier, + implementations MAY support one of the forms (either + issuerAndSerialNumber or subjectKeyIdentifier) and always use it, + or implementations MAY arbitrarily mix the two forms. However, + subjectKeyIdentifier MUST be used to refer to a public key + contained in a non-X.509 certificate. + + 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 in + section 5.4. The message digest algorithm SHOULD be among those + listed in the digestAlgorithms field of the associated SignerData. + Implementations MAY fail to validate signatures that use a digest + algorithm that is not included in the SignedData digestAlgorithms + set. + + signedAttrs 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. + SignedAttributes MUST be DER encoded, even if the rest of the + structure is BER encoded. Useful attribute types, such as signing + time, are defined in Section 11. If the field is present, it MUST + contain, at a minimum, the following two attributes: + + + + + +Housley Standards Track [Page 13] + +RFC 3852 Cryptographic Message Syntax July 2004 + + + A content-type attribute having as its value the content type + of the EncapsulatedContentInfo value being signed. Section + 11.1 defines the content-type attribute. However, the + content-type attribute MUST NOT be used as part of a + countersignature unsigned attribute as defined in section 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. The details of the + signature depend on the signature algorithm employed. + + unsignedAttrs is a collection of attributes that are not signed. + The field is optional. Useful attribute types, such as + countersignatures, are defined in Section 11. + + 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. The attrType can impose restrictions on the number of + items in the set. + +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 signedAttrs field is present. When the field is absent, + the result is just the message digest of the content as described + + + +Housley Standards Track [Page 14] + +RFC 3852 Cryptographic Message Syntax July 2004 + + + above. When the field is present, however, the result is the message + digest of the complete DER encoding of the SignedAttrs value + contained in the signedAttrs field. Since the SignedAttrs value, + when present, must contain the content-type and the message-digest + attributes, those values are indirectly included in the result. The + content-type attribute MUST NOT be included in a countersignature + unsigned attribute as defined in section 11.4. A separate encoding + of the signedAttrs field is performed for message digest calculation. + The IMPLICIT [0] tag in the signedAttrs is not used for the DER + encoding, rather an EXPLICIT SET OF tag is used. That is, the DER + encoding of the EXPLICIT SET OF tag, rather than of the IMPLICIT [0] + tag, MUST be included in the message digest calculation along with + the length and content octets of the SignedAttributes value. + + When the signedAttrs field is absent, 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. + + Although the encapContentInfo eContent OCTET STRING tag and length + octets are not included in the message digest calculation, they are + 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 message contents of any length + that have the same message digest. + +5.5. 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 MUST be encoded as an OCTET STRING and + carried in the signature field. + +5.6. 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 + + + + + +Housley Standards Track [Page 15] + +RFC 3852 Cryptographic Message Syntax July 2004 + + + 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 MUST 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 in section 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. + + If the SignedData signerInfo includes signedAttributes, then the + content-type attribute value MUST match the SignedData + encapContentInfo eContentType value. + +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 supported key + management techniques for each recipient. + + 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 four 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; + + + + + +Housley Standards Track [Page 16] + +RFC 3852 Cryptographic Message Syntax July 2004 + + + symmetric key-encryption keys: the content-encryption key is + encrypted in a previously distributed symmetric key-encryption + key; and + + passwords: the content-encryption key is encrypted in a key- + encryption key that is derived from a password or other shared + secret value. + + 3. For each recipient, the encrypted content-encryption key and + other recipient-specific information are collected into a + RecipientInfo value, defined in Section 6.2. + + 4. The content is encrypted with the content-encryption key. + Content encryption may require that the content be padded to a + multiple of some block size; see Section 6.3. + + 5. The RecipientInfo values for all the recipients are collected + together with the encrypted content to form an EnvelopedData + value as defined in Section 6.1. + + A recipient opens the digital envelope by decrypting one of the + encrypted content-encryption keys and then decrypting the + encrypted content with the recovered content-encryption key. + + This section is divided into four parts. The first part describes + the top-level type EnvelopedData, the second part describes the + per-recipient information type RecipientInfo, and the third and + fourth parts describe the content-encryption and key-encryption + processes. + +6.1. EnvelopedData Type + + The following object identifier identifies the enveloped-data content + type: + + id-envelopedData OBJECT IDENTIFIER ::= { iso(1) member-body(2) + us(840) rsadsi(113549) pkcs(1) pkcs7(7) 3 } + + The enveloped-data content type shall have ASN.1 type EnvelopedData: + + EnvelopedData ::= SEQUENCE { + version CMSVersion, + originatorInfo [0] IMPLICIT OriginatorInfo OPTIONAL, + recipientInfos RecipientInfos, + encryptedContentInfo EncryptedContentInfo, + unprotectedAttrs [1] IMPLICIT UnprotectedAttributes OPTIONAL } + + + + + +Housley Standards Track [Page 17] + +RFC 3852 Cryptographic Message Syntax July 2004 + + + OriginatorInfo ::= SEQUENCE { + certs [0] IMPLICIT CertificateSet OPTIONAL, + crls [1] IMPLICIT RevocationInfoChoices OPTIONAL } + + RecipientInfos ::= SET SIZE (1..MAX) OF RecipientInfo + + EncryptedContentInfo ::= SEQUENCE { + contentType ContentType, + contentEncryptionAlgorithm ContentEncryptionAlgorithmIdentifier, + encryptedContent [0] IMPLICIT EncryptedContent OPTIONAL } + + EncryptedContent ::= OCTET STRING + + UnprotectedAttributes ::= SET SIZE (1..MAX) OF Attribute + + The fields of type EnvelopedData have the following meanings: + + version is the syntax version number. The appropriate value + depends on originatorInfo, RecipientInfo, and unprotectedAttrs. + The version MUST be assigned as follows: + + IF (originatorInfo is present) AND + ((any certificates with a type of other are present) OR + (any crls with a type of other are present)) + THEN version is 4 + ELSE + IF ((originatorInfo is present) AND + (any version 2 attribute certificates are present)) OR + (any RecipientInfo structures include pwri) OR + (any RecipientInfo structures include ori) + THEN version is 3 + ELSE + IF (originatorInfo is absent) OR + (unprotectedAttrs is absent) OR + (all RecipientInfo structures are version 0) + THEN version is 0 + ELSE version is 2 + + 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 key + management algorithms. certs may also contain attribute + certificates associated with the originator. The certificates + contained in certs are intended to be sufficient for all + recipients to build certification paths from a recognized + + + +Housley Standards Track [Page 18] + +RFC 3852 Cryptographic Message Syntax July 2004 + + + "root" or "top-level certification authority." However, certs + may contain more certificates than necessary, and there may be + certificates sufficient to make certification paths 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 in Section 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 in Section + 6.3. The same content-encryption algorithm and content-encryption + key are 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 each of the supported key + management techniques. Any of the key management techniques can be + + + + + +Housley Standards Track [Page 19] + +RFC 3852 Cryptographic Message Syntax July 2004 + + + used for each recipient of the same encrypted content. In all cases, + the encrypted content-encryption key is transferred to one or more + recipients. + + Since all implementations will not support every possible key + management algorithm, all implementations MUST gracefully handle + unimplemented algorithms when they are encountered. For example, if + a recipient receives a content-encryption key encrypted in their RSA + public key using RSA-OAEP and the implementation only supports RSA + PKCS #1 v1.5, then a graceful failure must be implemented. + + Implementations MUST support key transport, key agreement, and + previously distributed symmetric key-encryption keys, as represented + by ktri, kari, and kekri, respectively. Implementations MAY support + the password-based key management as represented by pwri. + Implementations MAY support any other key management technique as + represented by ori. Since each recipient can employ a different key + management technique and future specifications could define + additional key management techniques, all implementations MUST + gracefully handle unimplemented alternatives within the RecipientInfo + CHOICE, all implementations MUST gracefully handle unimplemented + versions of otherwise supported alternatives within the RecipientInfo + CHOICE, and all implementations MUST gracefully handle unimplemented + or unknown ori alternatives. + + RecipientInfo ::= CHOICE { + ktri KeyTransRecipientInfo, + kari [1] KeyAgreeRecipientInfo, + kekri [2] KEKRecipientInfo, + pwri [3] PasswordRecipientinfo, + ori [4] OtherRecipientInfo } + + EncryptedKey ::= OCTET STRING + +6.2.1. 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 } + + + + + + +Housley Standards Track [Page 20] + +RFC 3852 Cryptographic Message Syntax July 2004 + + + 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 MUST be 0. + If the RecipientIdentifier is subjectKeyIdentifier, then the + version MUST be 2. + + rid specifies the recipient's certificate or key that was used by + the sender to protect the content-encryption key. The content- + encryption key is encrypted with the recipient's public 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. Therefore, a recipient X.509 version 3 certificate that + contains a key usage extension MUST assert the keyEncipherment + bit. 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 a key identifier. When an X.509 + certificate is referenced, the key identifier matches the X.509 + subjectKeyIdentifier extension value. When other certificate + formats are referenced, the documents that specify the certificate + format and their use with the CMS must include details on matching + the key identifier to the appropriate certificate field. For + recipient processing, implementations MUST support both of these + alternatives for specifying the recipient's certificate. For + sender processing, implementations MUST support at least one of + these alternatives. + + keyEncryptionAlgorithm identifies the key-encryption algorithm, + and any associated parameters, used to encrypt the content- + encryption key for the recipient. The key-encryption process is + described in Section 6.4. + + encryptedKey is the result of encrypting the content-encryption + key for the recipient. + +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 recipients that + use the same key agreement algorithm and domain parameters for that + algorithm. + + + +Housley Standards Track [Page 21] + +RFC 3852 Cryptographic Message Syntax July 2004 + + + 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 STRING + + The fields of type KeyAgreeRecipientInfo have the following meanings: + + version is the syntax version number. It MUST 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 + a key identifier. When an X.509 certificate is referenced, the + key identifier matches the X.509 subjectKeyIdentifier extension + + + +Housley Standards Track [Page 22] + +RFC 3852 Cryptographic Message Syntax July 2004 + + + value. When other certificate formats are referenced, the + documents that specify the certificate format and their use with + the CMS must include details on matching the key identifier to the + appropriate certificate field. The originatorKey alternative + includes the algorithm identifier and sender's key agreement + public key. This alternative permits originator anonymity since + the public key is not certified. Implementations MUST support all + three alternatives for specifying the sender's public key. + + 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. Implementations MUST accept a KeyAgreeRecipientInfo + SEQUENCE that includes a ukm field. Implementations that do not + support key agreement algorithms that make use of UKMs MUST + gracefully handle the presence of UKMs. + + 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 in Section 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. Therefore, a recipient X.509 + version 3 certificate that contains a key usage extension MUST + assert the keyAgreement bit. 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. Implementations MUST support both + alternatives for specifying the recipient's certificate. + + The fields of type RecipientKeyIdentifier have the following + meanings: + + subjectKeyIdentifier identifies the recipient's certificate by a + key identifier. When an X.509 certificate is referenced, the key + identifier matches the X.509 subjectKeyIdentifier extension value. + When other certificate formats are referenced, the documents that + + + + +Housley Standards Track [Page 23] + +RFC 3852 Cryptographic Message Syntax July 2004 + + + specify the certificate format and their use with the CMS must + include details on matching the key identifier to the appropriate + certificate field. + + 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 MUST 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 in Section 6.4. + + encryptedKey is the result of encrypting the content-encryption + key in the key-encryption key. + + + + + + + +Housley Standards Track [Page 24] + +RFC 3852 Cryptographic Message Syntax July 2004 + + + 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. + + other is optional. When present, this field contains additional + information used by the recipient to determine the key-encryption + key used by the sender. + +6.2.4. PasswordRecipientInfo Type + + Recipient information using a password or shared secret value is + represented in the type PasswordRecipientInfo. Each instance of + PasswordRecipientInfo will transfer the content-encryption key to one + or more recipients who possess the password or shared secret value. + + The PasswordRecipientInfo Type is specified in RFC 3211 [PWRI]. The + PasswordRecipientInfo structure is repeated here for completeness. + + PasswordRecipientInfo ::= SEQUENCE { + version CMSVersion, -- Always set to 0 + keyDerivationAlgorithm [0] KeyDerivationAlgorithmIdentifier + OPTIONAL, + keyEncryptionAlgorithm KeyEncryptionAlgorithmIdentifier, + encryptedKey EncryptedKey } + + The fields of type PasswordRecipientInfo have the following meanings: + + version is the syntax version number. It MUST always be 0. + + keyDerivationAlgorithm identifies the key-derivation algorithm, + and any associated parameters, used to derive the key-encryption + key from the password or shared secret value. If this field is + absent, the key-encryption key is supplied from an external + source, for example a hardware crypto token such as a smart card. + + keyEncryptionAlgorithm identifies the encryption algorithm, and + any associated parameters, used to encrypt the content-encryption + key with the key-encryption key. + + encryptedKey is the result of encrypting the content-encryption + key with the key-encryption key. + + + + + + +Housley Standards Track [Page 25] + +RFC 3852 Cryptographic Message Syntax July 2004 + + +6.2.5. OtherRecipientInfo Type + + Recipient information for additional key management techniques are + represented in the type OtherRecipientInfo. The OtherRecipientInfo + type allows key management techniques beyond key transport, key + agreement, previously distributed symmetric key-encryption keys, and + password-based key management to be specified in future documents. + An object identifier uniquely identifies such key management + techniques. + + OtherRecipientInfo ::= SEQUENCE { + oriType OBJECT IDENTIFIER, + oriValue ANY DEFINED BY oriType } + + The fields of type OtherRecipientInfo have the following meanings: + + oriType identifies the key management technique. + + oriValue contains the protocol data elements needed by a recipient + using the identified key management technique. + +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. + + 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 + + + + + + +Housley Standards Track [Page 26] + +RFC 3852 Cryptographic Message Syntax July 2004 + + + 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 aforementioned key management techniques can be used for + each recipient of the same encrypted content. + +7. Digested-data Content Type + + The digested-data content type consists of content of any type and a + message digest of the content. + + Typically, the digested-data content type is used to provide content + integrity, and the result generally becomes an input to the + enveloped-data content type. + + The following steps construct digested-data: + + 1. A message digest is computed on the content with a message- + digest algorithm. + + 2. The message-digest algorithm and the message digest are + collected together with the content into a DigestedData value. + + A recipient verifies the message digest by comparing the message + digest to an independently computed message digest. + + The following object identifier identifies the digested-data content + type: + + id-digestedData OBJECT IDENTIFIER ::= { iso(1) member-body(2) + us(840) rsadsi(113549) pkcs(1) pkcs7(7) 5 } + + + + + + + + + + + + +Housley Standards Track [Page 27] + +RFC 3852 Cryptographic Message Syntax July 2004 + + + 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 MUST be 0; however, if + the encapsulated content type is other than id-data, then the + value of version MUST 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 in Section 5.4 in the + case when there are no signed attributes. + + encapContentInfo is the content that is digested, as defined in + section 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 derived from 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 } + + + + +Housley Standards Track [Page 28] + +RFC 3852 Cryptographic Message Syntax July 2004 + + + 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 MUST be 2. If unprotectedAttrs is absent, + then version MUST be 0. + + encryptedContentInfo is the encrypted content information, as + defined in Section 6.1. + + unprotectedAttrs is a collection of attributes that are not + encrypted. The field is optional. Useful attribute types are + defined in Section 11. + +9. Authenticated-data Content Type + + The authenticated-data content type consists of content of any type, + a message authentication code (MAC), and encrypted authentication + keys for one or more recipients. The combination of the MAC and one + encrypted authentication key for a recipient is necessary for that + recipient to 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 in Section 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 (see Section 9.2), a + message digest is calculated on the content, the message digest + + + +Housley Standards Track [Page 29] + +RFC 3852 Cryptographic Message Syntax July 2004 + + + 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 } + + 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, + authAttrs [2] IMPLICIT AuthAttributes OPTIONAL, + mac MessageAuthenticationCode, + unauthAttrs [3] IMPLICIT UnauthAttributes OPTIONAL } + + AuthAttributes ::= SET SIZE (1..MAX) OF Attribute + + UnauthAttributes ::= SET SIZE (1..MAX) OF Attribute + + MessageAuthenticationCode ::= OCTET STRING + + The fields of type AuthenticatedData have the following meanings: + + version is the syntax version number. The version MUST be + assigned as follows: + + IF (originatorInfo is present) AND + ((any certificates with a type of other are present) OR + (any crls with a type of other are present)) + THEN version is 3 + ELSE + IF ((originatorInfo is present) AND + (any version 2 attribute certificates are present)) + THEN version is 1 + ELSE version is 0 + + + + +Housley Standards Track [Page 30] + +RFC 3852 Cryptographic Message Syntax July 2004 + + + 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 in Section 6.1. + + recipientInfos is a collection of per-recipient information, as + defined in Section 6.1. There MUST be at least one element in the + collection. + + macAlgorithm is a message authentication code (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 in Section 9.2. Placement + of the digestAlgorithm field facilitates one-pass processing by + the recipient. If the digestAlgorithm field is present, then the + authAttrs field MUST also be present. + + encapContentInfo is the content that is authenticated, as defined + in section 5.2. + + authAttrs is a collection of authenticated attributes. The + authAttrs structure is optional, but it MUST be present if the + content type of the EncapsulatedContentInfo value being + authenticated is not id-data. If the authAttrs field is present, + then the digestAlgorithm field MUST also be present. The + AuthAttributes structure MUST be DER encoded, even if the rest of + the structure is BER encoded. Useful attribute types are defined + in Section 11. If the authAttrs 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. + + + + + + +Housley Standards Track [Page 31] + +RFC 3852 Cryptographic Message Syntax July 2004 + + + unauthAttrs 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 in Section 11. + +9.2. MAC Generation + + The MAC calculation process computes a message authentication code + (MAC) on either the content being authenticated or a message digest + of content being authenticated together with the originator's + authenticated attributes. + + If authAttrs 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 authAttrs field is present, the content-type attribute (as + described in Section 11.1) and the message-digest attribute (as + described in section 11.2) MUST be included, and the input to the MAC + calculation process is the DER encoding of authAttrs. A separate + encoding of the authAttrs field is performed for message digest + calculation. The IMPLICIT [2] tag in the authAttrs 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 authAttrs 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 contents of any length that have + the same message digest. + + + + + +Housley Standards Track [Page 32] + +RFC 3852 Cryptographic Message Syntax July 2004 + + + 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 authAttrs 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 MUST NOT rely on any MAC values or message digest + values computed by the originator. The content is authenticated as + described in section 9.2. If the originator includes authenticated + attributes, then the content of the authAttrs is authenticated as + described in section 9.2. For authentication to succeed, the MAC + value calculated by the recipient MUST be the same as the value of + the mac field. Similarly, for authentication to succeed when the + authAttrs field is present, the content message digest value + calculated by the recipient MUST be the same as the message digest + value included in the authAttrs message-digest attribute. + + If the AuthenticatedData includes authAttrs, then the content-type + attribute value MUST match the AuthenticatedData encapContentInfo + eContentType value. + +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 taken + from X.509 [X.509-88]. + + There are many alternatives for each algorithm type. + + + + + +Housley Standards Track [Page 33] + +RFC 3852 Cryptographic Message Syntax July 2004 + + +10.1.1. DigestAlgorithmIdentifier + + The DigestAlgorithmIdentifier type identifies a message-digest + algorithm. Examples include SHA-1, MD2, and MD5. A message-digest + algorithm maps an octet string (the content) to another octet string + (the message digest). + + DigestAlgorithmIdentifier ::= AlgorithmIdentifier + +10.1.2. SignatureAlgorithmIdentifier + + The SignatureAlgorithmIdentifier type identifies a signature + algorithm. Examples include RSA, DSA, and ECDSA. A signature + algorithm supports signature generation and verification operations. + The signature generation operation uses the message digest and the + signer's private key to generate a signature value. The signature + verification operation uses the message digest and the signer's + public key to determine whether or not a signature value is valid. + Context determines which operation is intended. + + SignatureAlgorithmIdentifier ::= AlgorithmIdentifier + +10.1.3. KeyEncryptionAlgorithmIdentifier + + The KeyEncryptionAlgorithmIdentifier type identifies a key-encryption + algorithm used to encrypt a content-encryption key. The encryption + operation maps an octet string (the key) to another octet string (the + encrypted key) under control of a key-encryption key. The decryption + operation is the inverse of the encryption operation. Context + determines which operation is intended. + + The details of encryption and decryption depend on the key management + algorithm used. Key transport, key agreement, previously distributed + symmetric key-encrypting keys, and symmetric key-encrypting keys + derived from passwords are supported. + + KeyEncryptionAlgorithmIdentifier ::= AlgorithmIdentifier + +10.1.4. ContentEncryptionAlgorithmIdentifier + + The ContentEncryptionAlgorithmIdentifier type identifies a content- + encryption algorithm. Examples include Triple-DES and RC2. A + content-encryption algorithm supports encryption and decryption + operations. The encryption operation maps an octet string (the + plaintext) to another octet string (the ciphertext) under control of + + + + + + +Housley Standards Track [Page 34] + +RFC 3852 Cryptographic Message Syntax July 2004 + + + a content-encryption key. The decryption operation is the inverse of + the encryption operation. Context determines which operation is + intended. + + ContentEncryptionAlgorithmIdentifier ::= AlgorithmIdentifier + +10.1.5. MessageAuthenticationCodeAlgorithm + + The MessageAuthenticationCodeAlgorithm type identifies a message + authentication code (MAC) algorithm. Examples include DES-MAC and + HMAC-SHA-1. A MAC algorithm supports generation and verification + operations. The MAC generation and verification operations use the + same symmetric key. Context determines which operation is intended. + + MessageAuthenticationCodeAlgorithm ::= AlgorithmIdentifier + +10.1.6. KeyDerivationAlgorithmIdentifier + + The KeyDerivationAlgorithmIdentifier type is specified in RFC 3211 + [PWRI]. The KeyDerivationAlgorithmIdentifier definition is repeated + here for completeness. + + Key derivation algorithms convert a password or shared secret value + into a key-encryption key. + + KeyDerivationAlgorithmIdentifier ::= AlgorithmIdentifier + +10.2. Other Useful Types + + This section defines types that are used other places in the + document. The types are not listed in any particular order. + +10.2.1. RevocationInfoChoices + + The RevocationInfoChoices type gives a set of revocation status + information alternatives. It is intended that the set contain + information sufficient to determine whether the certificates and + attribute certificates with which the set is associated are revoked. + However, there MAY be more revocation status information than + necessary or there MAY be less revocation status information than + necessary. X.509 Certificate revocation lists (CRLs) [X.509-97] are + the primary source of revocation status information, but any other + revocation information format can be supported. The + OtherRevocationInfoFormat alternative is provided to support any + other revocation information format without further modifications to + the CMS. For example, Online Certificate Status Protocol (OCSP) + Responses [OCSP] can be supported using the + OtherRevocationInfoFormat. + + + +Housley Standards Track [Page 35] + +RFC 3852 Cryptographic Message Syntax July 2004 + + + The CertificateList may contain a CRL, an Authority Revocation List + (ARL), a Delta CRL, or an Attribute Certificate Revocation List. All + of these lists share a common syntax. + + The CertificateList type gives a certificate revocation list (CRL). + CRLs are specified in X.509 [X.509-97], and they are profiled for use + in the Internet in RFC 3280 [PROFILE]. + + The definition of CertificateList is taken from X.509. + + RevocationInfoChoices ::= SET OF RevocationInfoChoice + + RevocationInfoChoice ::= CHOICE { + crl CertificateList, + other [1] IMPLICIT OtherRevocationInfoFormat } + + OtherRevocationInfoFormat ::= SEQUENCE { + otherRevInfoFormat OBJECT IDENTIFIER, + otherRevInfo ANY DEFINED BY otherRevInfoFormat } + +10.2.2. CertificateChoices + + The CertificateChoices type gives either a PKCS #6 extended + certificate [PKCS#6], an X.509 certificate, a version 1 X.509 + attribute certificate (ACv1) [X.509-97], a version 2 X.509 attribute + certificate (ACv2) [X.509-00], or any other certificate format. The + PKCS #6 extended certificate is obsolete. The PKCS #6 certificate is + included for backward compatibility, and PKCS #6 certificates SHOULD + NOT be used. The ACv1 is also obsolete. ACv1 is included for + backward compatibility, and ACv1 SHOULD NOT be used. The Internet + profile of X.509 certificates is specified in the "Internet X.509 + Public Key Infrastructure: Certificate and CRL Profile" [PROFILE]. + The Internet profile of ACv2 is specified in the "An Internet + Attribute Certificate Profile for Authorization" [ACPROFILE]. The + OtherCertificateFormat alternative is provided to support any other + certificate format without further modifications to the CMS. + + The definition of Certificate is taken from X.509. + + The definitions of AttributeCertificate are taken from X.509-1997 and + X.509-2000. The definition from X.509-1997 is assigned to + AttributeCertificateV1 (see section 12.2), and the definition from + X.509-2000 is assigned to AttributeCertificateV2. + + + + + + + + +Housley Standards Track [Page 36] + +RFC 3852 Cryptographic Message Syntax July 2004 + + + CertificateChoices ::= CHOICE { + certificate Certificate, + extendedCertificate [0] IMPLICIT ExtendedCertificate, -- Obsolete + v1AttrCert [1] IMPLICIT AttributeCertificateV1, -- Obsolete + v2AttrCert [2] IMPLICIT AttributeCertificateV2, + other [3] IMPLICIT OtherCertificateFormat } + + OtherCertificateFormat ::= SEQUENCE { + otherCertFormat OBJECT IDENTIFIER, + otherCert ANY DEFINED BY otherCertFormat } + +10.2.3. CertificateSet + + The CertificateSet type provides a set of certificates. It is + intended that the set be sufficient to contain certification paths + from a recognized "root" or "top-level certification authority" to + all of the sender certificates with which the set is associated. + However, there may be more certificates than necessary, or there MAY + be fewer than necessary. + + The precise meaning of a "certification path" is outside the scope of + this document. However, [PROFILE] provides a definition for X.509 + certificates. Some applications may impose upper limits on the + length of a certification path; others may enforce certain + relationships between the subjects and issuers of certificates within + a certification path. + + CertificateSet ::= SET OF CertificateChoices + +10.2.4. IssuerAndSerialNumber + + The IssuerAndSerialNumber type identifies a certificate, and thereby + an entity and a public key, by the distinguished name of the + certificate issuer and an issuer-specific certificate serial number. + + The definition of Name is taken from X.501 [X.501-88], and the + definition of CertificateSerialNumber is taken from X.509 [X.509-97]. + + IssuerAndSerialNumber ::= SEQUENCE { + issuer Name, + serialNumber CertificateSerialNumber } + + CertificateSerialNumber ::= INTEGER + + + + + + + + +Housley Standards Track [Page 37] + +RFC 3852 Cryptographic Message Syntax July 2004 + + +10.2.5. CMSVersion + + The CMSVersion type gives a syntax version number, for compatibility + with future revisions of this specification. + + CMSVersion ::= INTEGER + { v0(0), v1(1), v2(2), v3(3), v4(4), v5(5) } + +10.2.6. UserKeyingMaterial + + The UserKeyingMaterial type gives a syntax for user keying material + (UKM). Some key agreement algorithms require UKMs to ensure that a + different key is generated each time the same two parties generate a + pairwise key. The sender provides a UKM for use with a specific key + agreement algorithm. + + UserKeyingMaterial ::= OCTET STRING + +10.2.7. OtherKeyAttribute + + The OtherKeyAttribute type gives a syntax for the inclusion of other + key attributes that permit the recipient to select the key used by + the sender. The attribute object identifier must be registered along + with the syntax of the attribute itself. Use of this structure + should be avoided since it might impede interoperability. + + OtherKeyAttribute ::= SEQUENCE { + keyAttrId OBJECT IDENTIFIER, + keyAttr ANY DEFINED BY keyAttrId OPTIONAL } + +11. Useful Attributes + + This section defines attributes that may be used with signed-data, + enveloped-data, encrypted-data, or authenticated-data. The syntax of + Attribute is compatible with X.501 [X.501-88] and RFC 3280 [PROFILE]. + Some of the attributes defined in this section were originally + defined in PKCS #9 [PKCS#9]; others were originally defined in a + previous version of this specification [CMS1]. The attributes are + not listed in any particular order. + + Additional attributes are defined in many places, notably the S/MIME + Version 3 Message Specification [MSG] and the Enhanced Security + Services for S/MIME [ESS], which also include recommendations on the + placement of these attributes. + + + + + + + +Housley Standards Track [Page 38] + +RFC 3852 Cryptographic Message Syntax July 2004 + + +11.1. Content Type + + The content-type attribute type specifies the content type of the + ContentInfo within signed-data or authenticated-data. The content- + type attribute type MUST be present whenever signed attributes are + present in signed-data or authenticated attributes present in + authenticated-data. The content-type attribute value MUST match the + encapContentInfo eContentType value in the signed-data or + authenticated-data. + + The content-type attribute MUST be a signed attribute or an + authenticated attribute; it MUST NOT be an unsigned attribute, + unauthenticated attribute, or unprotected attribute. + + The following object identifier identifies the content-type + attribute: + + id-contentType OBJECT IDENTIFIER ::= { iso(1) member-body(2) + us(840) rsadsi(113549) pkcs(1) pkcs9(9) 3 } + + Content-type attribute values have ASN.1 type ContentType: + + ContentType ::= OBJECT IDENTIFIER + + Even though the syntax is defined as a SET OF AttributeValue, a + content-type attribute MUST have a single attribute value; zero or + multiple instances of AttributeValue are not permitted. + + The SignedAttributes and AuthAttributes syntaxes are each defined as + a SET OF Attributes. The SignedAttributes in a signerInfo MUST NOT + include multiple instances of the content-type attribute. Similarly, + the AuthAttributes in an AuthenticatedData MUST NOT include multiple + instances of the content-type attribute. + +11.2. Message Digest + + The message-digest attribute type specifies the message digest of the + encapContentInfo eContent OCTET STRING being signed in signed-data + (see section 5.4) or authenticated in authenticated-data (see section + 9.2). For signed-data, the message digest is computed using the + signer's message digest algorithm. For authenticated-data, the + message digest is computed using the originator's message digest + algorithm. + + Within signed-data, the message-digest signed attribute type MUST be + present when there are any signed attributes present. Within + authenticated-data, the message-digest authenticated attribute type + MUST be present when there are any authenticated attributes present. + + + +Housley Standards Track [Page 39] + +RFC 3852 Cryptographic Message Syntax July 2004 + + + The message-digest attribute MUST be a signed attribute or an + authenticated attribute; it MUST NOT be an unsigned attribute, + unauthenticated attribute, or unprotected attribute. + + The following object identifier identifies the message-digest + attribute: + + id-messageDigest OBJECT IDENTIFIER ::= { iso(1) member-body(2) + us(840) rsadsi(113549) pkcs(1) pkcs9(9) 4 } + + Message-digest attribute values have ASN.1 type MessageDigest: + + MessageDigest ::= OCTET STRING + + A message-digest attribute MUST have a single attribute value, even + though the syntax is defined as a SET OF AttributeValue. There MUST + NOT be zero or multiple instances of AttributeValue present. + + The SignedAttributes syntax and AuthAttributes syntax are each + defined as a SET OF Attributes. The SignedAttributes in a signerInfo + MUST include only one instance of the message-digest attribute. + Similarly, the AuthAttributes in an AuthenticatedData MUST include + only one instance of the message-digest attribute. + +11.3. Signing Time + + The signing-time attribute type specifies the time at which the + signer (purportedly) performed the signing process. The signing-time + attribute type is intended for use in signed-data. + + The signing-time attribute MUST be a signed attribute or an + authenticated attribute; it MUST NOT be an unsigned attribute, + unauthenticated attribute, or unprotected attribute. + + The following object identifier identifies the signing-time + attribute: + + id-signingTime OBJECT IDENTIFIER ::= { iso(1) member-body(2) + us(840) rsadsi(113549) pkcs(1) pkcs9(9) 5 } + + Signing-time attribute values have ASN.1 type SigningTime: + + SigningTime ::= Time + + Time ::= CHOICE { + utcTime UTCTime, + generalizedTime GeneralizedTime } + + + + +Housley Standards Track [Page 40] + +RFC 3852 Cryptographic Message Syntax July 2004 + + + Note: The definition of Time matches the one specified in the 1997 + version of X.509 [X.509-97]. + + Dates between 1 January 1950 and 31 December 2049 (inclusive) MUST be + encoded as UTCTime. Any dates with year values before 1950 or after + 2049 MUST be encoded as GeneralizedTime. + + UTCTime values MUST be expressed in Coordinated Universal Time + (formerly known as Greenwich Mean Time (GMT) and Zulu clock time) and + MUST include seconds (i.e., times are YYMMDDHHMMSSZ), even where the + number of seconds is zero. Midnight MUST be represented as + "YYMMDD000000Z". Century information is implicit, and the century + MUST be determined as follows: + + Where YY is greater than or equal to 50, the year MUST be + interpreted as 19YY; and + + Where YY is less than 50, the year MUST be interpreted as 20YY. + + GeneralizedTime values MUST be expressed in Coordinated Universal + Time and MUST include seconds (i.e., times are YYYYMMDDHHMMSSZ), even + where the number of seconds is zero. GeneralizedTime values MUST NOT + include fractional seconds. + + A signing-time attribute MUST have a single attribute value, even + though the syntax is defined as a SET OF AttributeValue. There MUST + NOT be zero or multiple instances of AttributeValue present. + + The SignedAttributes syntax and the AuthAttributes syntax are each + defined as a SET OF Attributes. The SignedAttributes in a signerInfo + MUST NOT include multiple instances of the signing-time attribute. + Similarly, the AuthAttributes in an AuthenticatedData MUST NOT + include multiple instances of the signing-time attribute. + + No requirement is imposed concerning the correctness of the signing + time, and acceptance of a purported signing time is a matter of a + recipient's discretion. It is expected, however, that some signers, + such as time-stamp servers, will be trusted implicitly. + +11.4. Countersignature + + The countersignature attribute type specifies one or more signatures + on the contents octets of the signature OCTET STRING in a SignerInfo + value of the signed-data. That is, the message digest is computed + over the octets comprising the value of the OCTET STRING, neither the + tag nor length octets are included. Thus, the countersignature + attribute type countersigns (signs in serial) another signature. + + + + +Housley Standards Track [Page 41] + +RFC 3852 Cryptographic Message Syntax July 2004 + + + The countersignature attribute MUST be an unsigned attribute; it MUST + NOT be a signed attribute, an authenticated attribute, an + unauthenticated attribute, or an unprotected attribute. + + The following object identifier identifies the countersignature + attribute: + + id-countersignature OBJECT IDENTIFIER ::= { iso(1) member-body(2) + us(840) rsadsi(113549) pkcs(1) pkcs9(9) 6 } + + Countersignature attribute values have ASN.1 type Countersignature: + + Countersignature ::= SignerInfo + + Countersignature values have the same meaning as SignerInfo values + for ordinary signatures, except that: + + 1. The signedAttributes field MUST NOT contain a content-type + attribute; there is no content type for countersignatures. + + 2. The signedAttributes field MUST contain a message-digest + attribute if it contains any other attributes. + + 3. The input to the message-digesting process is the contents + octets of the DER encoding of the signatureValue field of the + SignerInfo value with which the attribute is associated. + + A countersignature attribute can have multiple attribute values. The + syntax is defined as a SET OF AttributeValue, and there MUST be one + or more instances of AttributeValue present. + + The UnsignedAttributes syntax is defined as a SET OF Attributes. The + UnsignedAttributes in a signerInfo may include multiple instances of + the countersignature attribute. + + A countersignature, since it has type SignerInfo, can itself contain + a countersignature attribute. Thus, it is possible to construct an + arbitrarily long series of countersignatures. + +12. ASN.1 Modules + + Section 12.1 contains the ASN.1 module for the CMS, and section 12.2 + contains the ASN.1 module for the Version 1 Attribute Certificate. + + + + + + + + +Housley Standards Track [Page 42] + +RFC 3852 Cryptographic Message Syntax July 2004 + + +12.1. CMS ASN.1 Module + + CryptographicMessageSyntax2004 + { iso(1) member-body(2) us(840) rsadsi(113549) + pkcs(1) pkcs-9(9) smime(16) modules(0) cms-2004(24) } + + DEFINITIONS IMPLICIT TAGS ::= + BEGIN + + -- EXPORTS All + -- The types and values defined in this module are exported for use + -- in the other ASN.1 modules. Other applications may use them for + -- their own purposes. + + IMPORTS + + -- Imports from RFC 3280 [PROFILE], Appendix A.1 + AlgorithmIdentifier, Certificate, CertificateList, + CertificateSerialNumber, Name + FROM PKIX1Explicit88 + { iso(1) identified-organization(3) dod(6) + internet(1) security(5) mechanisms(5) pkix(7) + mod(0) pkix1-explicit(18) } + + -- Imports from RFC 3281 [ACPROFILE], Appendix B + AttributeCertificate + FROM PKIXAttributeCertificate + { iso(1) identified-organization(3) dod(6) + internet(1) security(5) mechanisms(5) pkix(7) + mod(0) attribute-cert(12) } + + -- Imports from Appendix B of this document + AttributeCertificateV1 + FROM AttributeCertificateVersion1 + { iso(1) member-body(2) us(840) rsadsi(113549) + pkcs(1) pkcs-9(9) smime(16) modules(0) + v1AttrCert(15) } ; + + -- Cryptographic Message Syntax + + ContentInfo ::= SEQUENCE { + contentType ContentType, + content [0] EXPLICIT ANY DEFINED BY contentType } + + ContentType ::= OBJECT IDENTIFIER + + + + + + +Housley Standards Track [Page 43] + +RFC 3852 Cryptographic Message Syntax July 2004 + + + SignedData ::= SEQUENCE { + version CMSVersion, + digestAlgorithms DigestAlgorithmIdentifiers, + encapContentInfo EncapsulatedContentInfo, + certificates [0] IMPLICIT CertificateSet OPTIONAL, + crls [1] IMPLICIT RevocationInfoChoices OPTIONAL, + signerInfos SignerInfos } + + DigestAlgorithmIdentifiers ::= SET OF DigestAlgorithmIdentifier + + SignerInfos ::= SET OF SignerInfo + + EncapsulatedContentInfo ::= SEQUENCE { + eContentType ContentType, + eContent [0] EXPLICIT OCTET STRING OPTIONAL } + + SignerInfo ::= SEQUENCE { + version CMSVersion, + sid SignerIdentifier, + digestAlgorithm DigestAlgorithmIdentifier, + signedAttrs [0] IMPLICIT SignedAttributes OPTIONAL, + signatureAlgorithm SignatureAlgorithmIdentifier, + signature SignatureValue, + unsignedAttrs [1] IMPLICIT UnsignedAttributes OPTIONAL } + + SignerIdentifier ::= CHOICE { + issuerAndSerialNumber IssuerAndSerialNumber, + subjectKeyIdentifier [0] SubjectKeyIdentifier } + + SignedAttributes ::= SET SIZE (1..MAX) OF Attribute + + UnsignedAttributes ::= SET SIZE (1..MAX) OF Attribute + + Attribute ::= SEQUENCE { + attrType OBJECT IDENTIFIER, + attrValues SET OF AttributeValue } + + AttributeValue ::= ANY + + SignatureValue ::= OCTET STRING + + + + + + + + + + + +Housley Standards Track [Page 44] + +RFC 3852 Cryptographic Message Syntax July 2004 + + + 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 RevocationInfoChoices OPTIONAL } + + RecipientInfos ::= SET SIZE (1..MAX) OF RecipientInfo + + EncryptedContentInfo ::= SEQUENCE { + contentType ContentType, + contentEncryptionAlgorithm ContentEncryptionAlgorithmIdentifier, + encryptedContent [0] IMPLICIT EncryptedContent OPTIONAL } + + EncryptedContent ::= OCTET STRING + + UnprotectedAttributes ::= SET SIZE (1..MAX) OF Attribute + + RecipientInfo ::= CHOICE { + ktri KeyTransRecipientInfo, + kari [1] KeyAgreeRecipientInfo, + kekri [2] KEKRecipientInfo, + pwri [3] PasswordRecipientInfo, + ori [4] OtherRecipientInfo } + + EncryptedKey ::= OCTET STRING + + KeyTransRecipientInfo ::= SEQUENCE { + version CMSVersion, -- always set to 0 or 2 + rid RecipientIdentifier, + keyEncryptionAlgorithm KeyEncryptionAlgorithmIdentifier, + encryptedKey EncryptedKey } + + RecipientIdentifier ::= CHOICE { + issuerAndSerialNumber IssuerAndSerialNumber, + subjectKeyIdentifier [0] SubjectKeyIdentifier } + + KeyAgreeRecipientInfo ::= SEQUENCE { + version CMSVersion, -- always set to 3 + originator [0] EXPLICIT OriginatorIdentifierOrKey, + ukm [1] EXPLICIT UserKeyingMaterial OPTIONAL, + keyEncryptionAlgorithm KeyEncryptionAlgorithmIdentifier, + recipientEncryptedKeys RecipientEncryptedKeys } + + + + +Housley Standards Track [Page 45] + +RFC 3852 Cryptographic Message Syntax July 2004 + + + 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 STRING + + KEKRecipientInfo ::= SEQUENCE { + version CMSVersion, -- always set to 4 + kekid KEKIdentifier, + keyEncryptionAlgorithm KeyEncryptionAlgorithmIdentifier, + encryptedKey EncryptedKey } + + KEKIdentifier ::= SEQUENCE { + keyIdentifier OCTET STRING, + date GeneralizedTime OPTIONAL, + other OtherKeyAttribute OPTIONAL } + + PasswordRecipientInfo ::= SEQUENCE { + version CMSVersion, -- always set to 0 + keyDerivationAlgorithm [0] KeyDerivationAlgorithmIdentifier + OPTIONAL, + keyEncryptionAlgorithm KeyEncryptionAlgorithmIdentifier, + encryptedKey EncryptedKey } + + OtherRecipientInfo ::= SEQUENCE { + oriType OBJECT IDENTIFIER, + oriValue ANY DEFINED BY oriType } + + + + +Housley Standards Track [Page 46] + +RFC 3852 Cryptographic Message Syntax July 2004 + + + DigestedData ::= SEQUENCE { + version CMSVersion, + digestAlgorithm DigestAlgorithmIdentifier, + encapContentInfo EncapsulatedContentInfo, + digest Digest } + + Digest ::= OCTET STRING + + EncryptedData ::= SEQUENCE { + version CMSVersion, + encryptedContentInfo EncryptedContentInfo, + unprotectedAttrs [1] IMPLICIT UnprotectedAttributes OPTIONAL } + + AuthenticatedData ::= SEQUENCE { + version CMSVersion, + originatorInfo [0] IMPLICIT OriginatorInfo OPTIONAL, + recipientInfos RecipientInfos, + macAlgorithm MessageAuthenticationCodeAlgorithm, + digestAlgorithm [1] DigestAlgorithmIdentifier OPTIONAL, + encapContentInfo EncapsulatedContentInfo, + authAttrs [2] IMPLICIT AuthAttributes OPTIONAL, + mac MessageAuthenticationCode, + unauthAttrs [3] IMPLICIT UnauthAttributes OPTIONAL } + + AuthAttributes ::= SET SIZE (1..MAX) OF Attribute + + UnauthAttributes ::= SET SIZE (1..MAX) OF Attribute + + MessageAuthenticationCode ::= OCTET STRING + + DigestAlgorithmIdentifier ::= AlgorithmIdentifier + + SignatureAlgorithmIdentifier ::= AlgorithmIdentifier + + KeyEncryptionAlgorithmIdentifier ::= AlgorithmIdentifier + + ContentEncryptionAlgorithmIdentifier ::= AlgorithmIdentifier + + MessageAuthenticationCodeAlgorithm ::= AlgorithmIdentifier + + KeyDerivationAlgorithmIdentifier ::= AlgorithmIdentifier + + RevocationInfoChoices ::= SET OF RevocationInfoChoice + + RevocationInfoChoice ::= CHOICE { + crl CertificateList, + other [1] IMPLICIT OtherRevocationInfoFormat } + + + + +Housley Standards Track [Page 47] + +RFC 3852 Cryptographic Message Syntax July 2004 + + + OtherRevocationInfoFormat ::= SEQUENCE { + otherRevInfoFormat OBJECT IDENTIFIER, + otherRevInfo ANY DEFINED BY otherRevInfoFormat } + + CertificateChoices ::= CHOICE { + certificate Certificate, + extendedCertificate [0] IMPLICIT ExtendedCertificate, -- Obsolete + v1AttrCert [1] IMPLICIT AttributeCertificateV1, -- Obsolete + v2AttrCert [2] IMPLICIT AttributeCertificateV2, + other [3] IMPLICIT OtherCertificateFormat } + + AttributeCertificateV2 ::= AttributeCertificate + + OtherCertificateFormat ::= SEQUENCE { + otherCertFormat OBJECT IDENTIFIER, + otherCert ANY DEFINED BY otherCertFormat } + + CertificateSet ::= SET OF CertificateChoices + + IssuerAndSerialNumber ::= SEQUENCE { + issuer Name, + serialNumber CertificateSerialNumber } + + CMSVersion ::= INTEGER { v0(0), v1(1), v2(2), v3(3), v4(4), v5(5) } + + UserKeyingMaterial ::= OCTET STRING + + OtherKeyAttribute ::= SEQUENCE { + keyAttrId OBJECT IDENTIFIER, + keyAttr ANY DEFINED BY keyAttrId OPTIONAL } + + -- Content Type Object Identifiers + + id-ct-contentInfo OBJECT IDENTIFIER ::= { iso(1) member-body(2) + us(840) rsadsi(113549) pkcs(1) pkcs9(9) smime(16) ct(1) 6 } + + id-data OBJECT IDENTIFIER ::= { iso(1) member-body(2) + us(840) rsadsi(113549) pkcs(1) pkcs7(7) 1 } + + id-signedData OBJECT IDENTIFIER ::= { iso(1) member-body(2) + us(840) rsadsi(113549) pkcs(1) pkcs7(7) 2 } + + id-envelopedData OBJECT IDENTIFIER ::= { iso(1) member-body(2) + us(840) rsadsi(113549) pkcs(1) pkcs7(7) 3 } + + id-digestedData OBJECT IDENTIFIER ::= { iso(1) member-body(2) + us(840) rsadsi(113549) pkcs(1) pkcs7(7) 5 } + + + + +Housley Standards Track [Page 48] + +RFC 3852 Cryptographic Message Syntax July 2004 + + + 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 } + + -- The CMS Attributes + + MessageDigest ::= OCTET STRING + + SigningTime ::= Time + + Time ::= CHOICE { + utcTime UTCTime, + generalTime GeneralizedTime } + + Countersignature ::= SignerInfo + + -- Attribute Object Identifiers + + id-contentType OBJECT IDENTIFIER ::= { iso(1) member-body(2) + us(840) rsadsi(113549) pkcs(1) pkcs9(9) 3 } + + id-messageDigest OBJECT IDENTIFIER ::= { iso(1) member-body(2) + us(840) rsadsi(113549) pkcs(1) pkcs9(9) 4 } + + id-signingTime OBJECT IDENTIFIER ::= { iso(1) member-body(2) + us(840) rsadsi(113549) pkcs(1) pkcs9(9) 5 } + + id-countersignature OBJECT IDENTIFIER ::= { iso(1) member-body(2) + us(840) rsadsi(113549) pkcs(1) pkcs9(9) 6 } + + -- Obsolete Extended Certificate syntax from PKCS#6 + + ExtendedCertificateOrCertificate ::= CHOICE { + certificate Certificate, + extendedCertificate [0] IMPLICIT ExtendedCertificate } + + ExtendedCertificate ::= SEQUENCE { + extendedCertificateInfo ExtendedCertificateInfo, + signatureAlgorithm SignatureAlgorithmIdentifier, + signature Signature } + + + + + + + + + +Housley Standards Track [Page 49] + +RFC 3852 Cryptographic Message Syntax July 2004 + + + ExtendedCertificateInfo ::= SEQUENCE { + version CMSVersion, + certificate Certificate, + attributes UnauthAttributes } + + Signature ::= BIT STRING + + END -- of CryptographicMessageSyntax2004 + +12.2. Version 1 Attribute Certificate ASN.1 Module + + AttributeCertificateVersion1 + { iso(1) member-body(2) us(840) rsadsi(113549) + pkcs(1) pkcs-9(9) smime(16) modules(0) v1AttrCert(15) } + + DEFINITIONS EXPLICIT TAGS ::= + BEGIN + + -- EXPORTS All + + IMPORTS + + -- Imports from RFC 3280 [PROFILE], Appendix A.1 + AlgorithmIdentifier, Attribute, CertificateSerialNumber, + Extensions, UniqueIdentifier + FROM PKIX1Explicit88 + { iso(1) identified-organization(3) dod(6) + internet(1) security(5) mechanisms(5) pkix(7) + mod(0) pkix1-explicit(18) } + + -- Imports from RFC 3280 [PROFILE], Appendix A.2 + GeneralNames + FROM PKIX1Implicit88 + { iso(1) identified-organization(3) dod(6) + internet(1) security(5) mechanisms(5) pkix(7) + mod(0) pkix1-implicit(19) } + + -- Imports from RFC 3281 [ACPROFILE], Appendix B + AttCertValidityPeriod, IssuerSerial + FROM PKIXAttributeCertificate + { iso(1) identified-organization(3) dod(6) + internet(1) security(5) mechanisms(5) pkix(7) + mod(0) attribute-cert(12) } ; + + -- Definition extracted from X.509-1997 [X.509-97], but + -- different type names are used to avoid collisions. + + + + + +Housley Standards Track [Page 50] + +RFC 3852 Cryptographic Message Syntax July 2004 + + + AttributeCertificateV1 ::= SEQUENCE { + acInfo AttributeCertificateInfoV1, + signatureAlgorithm AlgorithmIdentifier, + signature BIT STRING } + + AttributeCertificateInfoV1 ::= SEQUENCE { + version AttCertVersionV1 DEFAULT v1, + subject CHOICE { + baseCertificateID [0] IssuerSerial, + -- associated with a Public Key Certificate + subjectName [1] GeneralNames }, + -- associated with a name + issuer GeneralNames, + signature AlgorithmIdentifier, + serialNumber CertificateSerialNumber, + attCertValidityPeriod AttCertValidityPeriod, + attributes SEQUENCE OF Attribute, + issuerUniqueID UniqueIdentifier OPTIONAL, + extensions Extensions OPTIONAL } + + AttCertVersionV1 ::= INTEGER { v1(0) } + + END -- of AttributeCertificateVersion1 + +13. References + +13.1. Normative References + + [ACPROFILE] Farrell, S. and R. Housley, "An Internet Attribute + Certificate Profile for Authorization", RFC 3281, April + 2002. + + [PROFILE] Housley, R., Polk, W., Ford, W., and D. Solo, "Internet + X.509 Public Key Infrastructure Certificate and + Certificate Revocation List (CRL) Profile", RFC 3280, + April 2002. + + [STDWORDS] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", BCP 14, RFC 2119, March 1997. + + [X.208-88] CCITT. Recommendation X.208: Specification of Abstract + Syntax Notation One (ASN.1). 1988. + + [X.209-88] CCITT. Recommendation X.209: Specification of Basic + Encoding Rules for Abstract Syntax Notation One (ASN.1). + 1988. + + + + + +Housley Standards Track [Page 51] + +RFC 3852 Cryptographic Message Syntax July 2004 + + + [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. + + [X.509-00] ITU-T. Recommendation X.509: The Directory - + Authentication Framework. 2000. + +13.2. Informative References + + [CMS1] Housley, R., "Cryptographic Message Syntax", RFC 2630, + June 1999. + + [CMS2] Housley, R., "Cryptographic Message Syntax (CMS)", RFC + 3369, August 2002. + + [CMSALG] Housley, R., "Cryptographic Message Syntax (CMS) + Algorithms", RFC 3370, August 2002. + + [ESS] Hoffman, P., "Enhanced Security Services for S/MIME", + RFC 2634, June 1999. + + [MSAC] Microsoft Development Network (MSDN) Library, + "Authenticode", April 2004 Release. + + [MSG] Ramsdell, B., "S/MIME Version 3.1 Message + Specification", RFC 3851, July 2004. + + [OCSP] Myers, M., Ankney, R., Malpani, A., Galperin, S. and C. + Adams, "X.509 Internet Public Key Infrastructure Online + Certificate Status Protocol - OCSP", RFC 2560, June + 1999. + + [OLDMSG] Dusse, S., Hoffman, P., Ramsdell, B., Lundblade, L., and + L. Repka, "S/MIME Version 2 Message Specification", RFC + 2311, 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. + + + + + +Housley Standards Track [Page 52] + +RFC 3852 Cryptographic Message Syntax July 2004 + + + [PKCS#9] RSA Laboratories. PKCS #9: Selected Attribute Types, + Version 1.1. November 1993. + + [PWRI] Gutmann, P., "Password-based Encryption for CMS", RFC + 3211, December 2001. + + [RANDOM] Eastlake 3rd, D., Crocker, S., and J. Schiller, + "Randomness Recommendations for Security", RFC 1750, + December 1994. + +14. Security Considerations + + The Cryptographic Message Syntax provides a method for digitally + signing data, digesting data, encrypting data, and authenticating + data. + + Implementations must protect the signer's private key. Compromise of + the signer's private key permits masquerade. + + Implementations must protect the key management private key, the + key-encryption key, and the content-encryption key. Compromise of + the key management private key or the key-encryption key may result + in the disclosure of all contents protected with that key. + Similarly, compromise of the content-encryption key may result in + disclosure of the associated encrypted content. + + Implementations must protect the key management private key and the + message-authentication key. Compromise of the key management private + key permits masquerade of authenticated data. Similarly, compromise + of the message-authentication key may result in undetectable + modification of the authenticated content. + + The key management technique employed to distribute message- + authentication keys must itself provide data origin authentication, + otherwise the contents are delivered with integrity from an unknown + source. Neither RSA [PKCS#1, NEWPKCS#1] nor Ephemeral-Static + Diffie-Hellman [DH-X9.42] provide the necessary data origin + authentication. Static-Static Diffie-Hellman [DH-X9.42] does provide + the necessary data origin authentication when both the originator and + recipient public keys are bound to appropriate identities in X.509 + certificates. + + When more than two parties share the same message-authentication key, + data origin authentication is not provided. Any party that knows the + message-authentication key can compute a valid MAC, therefore the + contents could originate from any one of the parties. + + + + + +Housley Standards Track [Page 53] + +RFC 3852 Cryptographic Message Syntax July 2004 + + + 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. + + When using key agreement algorithms or previously distributed + symmetric key-encryption keys, a key-encryption key is used to + encrypt the content-encryption key. If the key-encryption and + content-encryption algorithms are different, the effective security + is determined by the weaker of the two algorithms. If, for example, + content is encrypted with Triple-DES using a 168-bit Triple-DES + content-encryption key, and the content-encryption key is wrapped + with RC2 using a 40-bit RC2 key-encryption key, then at most 40 bits + of protection is provided. A trivial search to determine the value + of the 40-bit RC2 key can recover the Triple-DES key, and then the + Triple-DES key can be used to decrypt the content. Therefore, + implementers must ensure that key-encryption algorithms are as strong + or stronger than content-encryption algorithms. + + Implementers should be aware that cryptographic algorithms become + weaker with time. As new cryptoanalysis techniques are developed and + computing performance improves, the work factor to break a particular + cryptographic algorithm will be reduced. Therefore, cryptographic + algorithm implementations should be modular, allowing new algorithms + to be readily inserted. That is, implementors should be prepared for + the set of algorithms that must be supported to change over time. + + The countersignature unsigned attribute includes a digital signature + that is computed on the content signature value, thus the + countersigning process need not know the original signed content. + This structure permits implementation efficiency advantages; however, + this structure may also permit the countersigning of an inappropriate + signature value. Therefore, implementations that perform + countersignatures should either verify the original signature value + prior to countersigning it (this verification requires processing of + the original content), or implementations should perform + countersigning in a context that ensures that only appropriate + signature values are countersigned. + + + + + + +Housley Standards Track [Page 54] + +RFC 3852 Cryptographic Message Syntax July 2004 + + +15. Acknowledgments + + This document is the result of contributions from many professionals. + I appreciate the hard work of all members of the IETF S/MIME Working + Group. I extend a special thanks to Rich Ankney, Simon Blake-Wilson, + Tim Dean, Steve Dusse, Carl Ellison, Peter Gutmann, Bob Jueneman, + Stephen Henson, Paul Hoffman, Scott Hollenbeck, Don Johnson, Burt + Kaliski, John Linn, John Pawling, Blake Ramsdell, Francois Rousseau, + Jim Schaad, Dave Solo, Paul Timmel, and Sean Turner for their efforts + and support. + +16. Author's Address + + Russell Housley + Vigil Security, LLC + 918 Spring Knoll Drive + Herndon, VA 20170 + USA + + EMail: housley@vigilsec.com + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Housley Standards Track [Page 55] + +RFC 3852 Cryptographic Message Syntax July 2004 + + +17. Full Copyright Statement + + Copyright (C) The Internet Society (2004). This document is subject + to the rights, licenses and restrictions contained in BCP 78, and + except as set forth therein, the authors retain all their rights. + + This document and the information contained herein are provided on an + "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS + OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET + ENGINEERING TASK FORCE DISCLAIM 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. + +Intellectual Property + + The IETF takes no position regarding the validity or scope of any + Intellectual Property Rights or other rights that might be claimed to + pertain to the implementation or use of the technology described in + this document or the extent to which any license under such rights + might or might not be available; nor does it represent that it has + made any independent effort to identify any such rights. Information + on the procedures with respect to rights in RFC documents can be + found in BCP 78 and BCP 79. + + Copies of IPR disclosures made to the IETF Secretariat and any + assurances of licenses to be made available, or the result of an + attempt made to obtain a general license or permission for the use of + such proprietary rights by implementers or users of this + specification can be obtained from the IETF on-line IPR repository at + http://www.ietf.org/ipr. + + The IETF invites any interested party to bring to its attention any + copyrights, patents or patent applications, or other proprietary + rights that may cover technology that may be required to implement + this standard. Please address the information to the IETF at ietf- + ipr@ietf.org. + +Acknowledgement + + Funding for the RFC Editor function is currently provided by the + Internet Society. + + + + + + + + + +Housley Standards Track [Page 56] + |