rfc2630.txt

著名的RFC文档,其中有一些文档是已经翻译成中文的的.

Network Working Group                                        R. Housley
Request for Comments: 2630                                       SPYRUS
Category: Standards Track                                     June 1999


                      Cryptographic Message Syntax

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 (1999).  All Rights Reserved.

Abstract

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

   The Cryptographic Message Syntax is derived from PKCS #7 version 1.5
   as specified in RFC 2315 [PKCS#7].  Wherever possible, backward
   compatibility is preserved; however, changes were necessary to
   accommodate attribute certificate transfer and key agreement
   techniques for key management.





















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RFC 2630              Cryptographic Message Syntax             June 1999


Table of Contents

   1   Introduction .................................................  4
   2   General Overview .............................................  4
   3   General Syntax ...............................................  5
   4   Data Content Type ............................................  5
   5   Signed-data Content Type .....................................  6
       5.1  SignedData Type .........................................  7
       5.2  EncapsulatedContentInfo Type ............................  8
       5.3  SignerInfo Type .........................................  9
       5.4  Message Digest Calculation Process ...................... 11
       5.5  Message Signature Generation Process .................... 12
       5.6  Message Signature Verification Process .................. 12
   6   Enveloped-data Content Type .................................. 12
       6.1  EnvelopedData Type ...................................... 14
       6.2  RecipientInfo Type ...................................... 15
            6.2.1  KeyTransRecipientInfo Type ....................... 16
            6.2.2  KeyAgreeRecipientInfo Type ....................... 17
            6.2.3  KEKRecipientInfo Type ............................ 19
       6.3  Content-encryption Process .............................. 20
       6.4  Key-encryption Process .................................. 20
   7   Digested-data Content Type ................................... 21
   8   Encrypted-data Content Type .................................. 22
   9   Authenticated-data Content Type .............................. 23
       9.1  AuthenticatedData Type .................................. 23
       9.2  MAC Generation .......................................... 25
       9.3  MAC Verification ........................................ 26
   10  Useful Types ................................................. 27
       10.1  Algorithm Identifier Types ............................. 27
             10.1.1  DigestAlgorithmIdentifier ...................... 27
             10.1.2  SignatureAlgorithmIdentifier ................... 27
             10.1.3  KeyEncryptionAlgorithmIdentifier ............... 28
             10.1.4  ContentEncryptionAlgorithmIdentifier ........... 28
             10.1.5  MessageAuthenticationCodeAlgorithm ............. 28
       10.2  Other Useful Types ..................................... 28
             10.2.1  CertificateRevocationLists ..................... 28
             10.2.2  CertificateChoices ............................. 29
             10.2.3  CertificateSet ................................. 29
             10.2.4  IssuerAndSerialNumber .......................... 30
             10.2.5  CMSVersion ..................................... 30
             10.2.6  UserKeyingMaterial ............................. 30
             10.2.7  OtherKeyAttribute .............................. 30









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   11  Useful Attributes ............................................ 31
       11.1  Content Type ........................................... 31
       11.2  Message Digest ......................................... 32
       11.3  Signing Time ........................................... 32
       11.4  Countersignature ....................................... 34
   12  Supported Algorithms ......................................... 35
       12.1  Digest Algorithms ...................................... 35
             12.1.1  SHA-1 .......................................... 35
             12.1.2  MD5 ............................................ 35
       12.2  Signature Algorithms ................................... 36
             12.2.1  DSA ............................................ 36
             12.2.2  RSA ............................................ 36
       12.3  Key Management Algorithms .............................. 36
             12.3.1  Key Agreement Algorithms ....................... 36
                     12.3.1.1  X9.42 Ephemeral-Static Diffie-Hellman. 37
             12.3.2  Key Transport Algorithms ....................... 38
                     12.3.2.1  RSA .................................. 39
             12.3.3  Symmetric Key-Encryption Key Algorithms ........ 39
                     12.3.3.1  Triple-DES Key Wrap .................. 40
                     12.3.3.2  RC2 Key Wrap ......................... 41
      12.4  Content Encryption Algorithms ........................... 41
            12.4.1  Triple-DES CBC .................................. 42
            12.4.2  RC2 CBC ......................................... 42
      12.5  Message Authentication Code Algorithms .................. 42
            12.5.1  HMAC with SHA-1 ................................. 43
      12.6  Triple-DES and RC2 Key Wrap Algorithms .................. 43
            12.6.1  Key Checksum .................................... 44
            12.6.2  Triple-DES Key Wrap ............................. 44
            12.6.3  Triple-DES Key Unwrap ........................... 44
            12.6.4  RC2 Key Wrap .................................... 45
            12.6.5  RC2 Key Unwrap .................................. 46
   Appendix A:  ASN.1 Module ........................................ 47
   References ....................................................... 55
   Security Considerations .......................................... 56
   Acknowledgments .................................................. 58
   Author's Address ................................................. 59
   Full Copyright Statement ......................................... 60














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RFC 2630              Cryptographic Message Syntax             June 1999


1  Introduction

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

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

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

   The Cryptographic Message Syntax values are generated using ASN.1
   [X.208-88], using BER-encoding [X.209-88].  Values are typically
   represented as octet strings.  While many systems are capable of
   transmitting arbitrary octet strings reliably, it is well known that
   many electronic-mail systems are not.  This document does not address
   mechanisms for encoding octet strings for reliable transmission in
   such environments.

2  General Overview

   The Cryptographic Message Syntax (CMS) is general enough to support
   many different content types.  This document defines one protection
   content, ContentInfo.  ContentInfo encapsulates a single identified
   content type, and the identified type may provide further
   encapsulation.  This document defines six content types: data,
   signed-data, enveloped-data, digested-data, encrypted-data, and
   authenticated-data.  Additional content types can be defined outside
   this document.

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

   As a general design philosophy, each content type permits single pass
   processing using indefinite-length Basic Encoding Rules (BER)
   encoding.  Single-pass operation is especially helpful if content is
   large, stored on tapes, or is "piped" from another process.  Single-



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RFC 2630              Cryptographic Message Syntax             June 1999


   pass operation has one significant drawback: it is difficult to
   perform encode operations using the Distinguished Encoding Rules
   (DER) [X.509-88] encoding in a single pass since the lengths of the
   various components may not be known in advance.  However, signed
   attributes within the signed-data content type and authenticated
   attributes within the authenticated-data content type require DER
   encoding.  Signed attributes and authenticated attributes must be
   transmitted in DER form to ensure that recipients can verify a
   content that contains one or more unrecognized attributes.  Signed
   attributes and authenticated attributes are the only CMS data types
   that require DER encoding.

3  General Syntax

   The Cryptographic Message Syntax (CMS) associates a content type
   identifier with a content.  The syntax shall have ASN.1 type
   ContentInfo:

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

      ContentType ::= OBJECT IDENTIFIER

   The fields of ContentInfo have the following meanings:

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

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

4  Data Content Type

   The following object identifier identifies the data content type:

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

   The data content type is intended to refer to arbitrary octet
   strings, such as ASCII text files; the interpretation is left to the
   application.  Such strings need not have any internal structure




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   (although they could have their own ASN.1 definition or other
   structure).

   The data content type is generally encapsulated in the signed-data,
   enveloped-data, digested-data, encrypted-data, or authenticated-data
   content type.

5  Signed-data Content Type

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

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

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

      1.  For each signer, a message digest, or hash value, is computed
      on the content with a signer-specific message-digest algorithm.
      If the signer is signing any information other than the content,
      the message digest of the content and the other information are
      digested with the signer's message digest algorithm (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.