[Docs] [txt|pdf] [Tracker] [Email] [Diff1] [Diff2] [Nits]

Versions: 00 01 02 03 04 05 RFC 4073

Network Working Group                                        R. Housley
Internet Draft                                           Vigil Security
expires in six months                                     November 2004


                 Protecting Multiple Contents with the
                   Cryptographic Message Syntax (CMS)

                <draft-housley-contentcollection-05.txt>

Status of this Memo

   By submitting this Internet-Draft, I certify that any applicable
   patent or other IPR claims of which I am aware have been disclosed,
   or will be disclosed, and any of which I become aware will be
   disclosed, in accordance with RFC 3668.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than a "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/1id-abstracts.html

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html

IPR Statement

   By submitting this Internet-Draft, I certify that any applicable
   patent or other IPR claims of which I am aware have been disclosed,
   or will be disclosed, and any of which I become aware will be
   disclosed, in accordance with RFC 3668.

Abstract

   This document describes a convention for using the Cryptographic
   Message Syntax (CMS) to protect more than one content.  If desired,
   attributes can be associated with the content.






Housley                                                         [Page 1]

INTERNET DRAFT                                             November 2004


1  Introduction

   This document describes a convention for using the Cryptographic
   Message Syntax (CMS) [CMS] to protect more than one content.  The
   content collection content type is used to transfer one or more
   contents, each identified by a content type.  If desired, the content
   with attributes content type can be used to associate arbitrary
   attributes with the content.

   When CMS is used with MIME [MSG], there is no need to use this
   specification.  In this processing environment, MIME multipart [MIME]
   provides a straightforward and widely deployed mechanism for carrying
   more than one content, each associated with a MIME type.

   CMS is not always used with MIME.  Sometimes CMS is used in an
   exclusively ASN.1 [ASN1] environment.  In this case, the content
   collection content type is used to gather more than one content, each
   with an object identifier to provide the content type.

1.1  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].

1.2  Content Collection Example

   This section provides one simple example to motivate the need for the
   content collection content type.

   Consider an art collector who wants to sell one of his pieces, an
   ancient Greek urn, called an amphora.  The collector wants to compose
   a digitally signed offer for sale.  It includes three parts.  The
   first part contains the owner's offer for sale, including the asking
   price.  The second part contains a high-quality image of the amphora.
   The final part contains an appraisal from a well-respected ceramics
   expert.  The final part is digitally signed by the expert.  Figure 1
   illustrates the structure, and the CMS SignedData content type is
   used for the two digital signatures.












Housley                                                         [Page 2]

INTERNET DRAFT                                             November 2004


   +---------------------------------------------------------+
   |                                                         |
   | ContentInfo                                             |
   |                                                         |
   | +-----------------------------------------------------+ |
   | |                                                     | |
   | | SignedData                                          | |
   | |                                                     | |
   | | +-------------------------------------------------+ | |
   | | |                                                 | | |
   | | | ContentCollection                               | | |
   | | |                                                 | | |
   | | | +-----------+ +-----------+ +-----------------+ | | |
   | | | |           | |           | |                 | | | |
   | | | | Owner's   | | Image     | | SignedData      | | | |
   | | | | Offer to  | | of the    | |                 | | | |
   | | | | Sell the  | | Amphora   | | +-------------+ | | | |
   | | | | Amphora   | |           | | |             | | | | |
   | | | |           | |           | | | Appraisal   | | | | |
   | | | |           | |           | | | of Ceramics | | | | |
   | | | |           | |           | | | Expert      | | | | |
   | | | |           | |           | | |             | | | | |
   | | | |           | |           | | +-------------+ | | | |
   | | | |           | |           | |                 | | | |
   | | | +-----------+ +-----------+ +-----------------+ | | |
   | | |                                                 | | |
   | | +-------------------------------------------------+ | |
   | |                                                     | |
   | +-----------------------------------------------------+ |
   |                                                         |
   +---------------------------------------------------------+


   Figure 1.  Sample use of the ContentCollection Content Type.


1.3  Content with Attributes Example

   This section provides one simple example to motivate the need for the
   content with attributes content type.

   Consider the same art collector as in the previous example.  Instead
   of providing a single image of the amphora, the collector provides
   several images.  To aid potential buyers, the collector attaches
   several attributes to each image.  The attributes provide information
   about the resolution of the image, the date the image was taken, the
   photographer, and so on.  Figure 2 illustrates the collection of
   images, showing only two images, each with three attributes.  This



Housley                                                         [Page 3]

INTERNET DRAFT                                             November 2004


   entire image content collection could be carried instead of the
   single image shown in Figure 1, allowing it to be covered by the
   collector's digital signature.


   +----------------------------------------------------------+
   |                                                          |
   | ContentCollection                                        |
   |                                                          |
   | +-------------------------+  +-------------------------+ |
   | |                         |  |                         | |
   | | ContentWithAttributes   |  | ContentWithAttributes   | |
   | |                         |  |                         | |
   | | +---------------------+ |  | +---------------------+ | |
   | | |                     | |  | |                     | | |
   | | | First Image of      | |  | | Second Image of     | | |
   | | | the Amphora         | |  | | the Amphora         | | |
   | | |                     | |  | |                     | | |
   | | |                     | |  | |                     | | |
   | | +---------------------+ |  | +---------------------+ | |
   | |                         |  |                         | |
   | | +---------------+       |  | +---------------+       | |
   | | |               |       |  | |               |       | |
   | | | Attribute 1   |       |  | | Attribute 1   |       | |
   | | |               +--+    |  | |               +--+    | |
   | | +-+-------------+  |    |  | +-+-------------+  |    | |
   | |   | Attribute 2    |    |  |   | Attribute 2    |    | |
   | |   |                +--+ |  |   |                +--+ | |
   | |   +-+--------------+  | |  |   +-+--------------+  | | |
   | |     | Attribute 3     | |  |     | Attribute 3     | | |
   | |     |                 | |  |     |                 | | |
   | |     +-----------------+ |  |     +-----------------+ | |
   | |                         |  |                         | |
   | +-------------------------+  +-------------------------+ |
   |                                                          |
   +----------------------------------------------------------+


   Figure 2.  Sample use of the ContentWithAttributes Content Type.


2  Content Collection Content Type

   The content collection content type is used to transfer one or more
   contents, each identified by a content type.  The syntax accommodates
   contents with varying levels of protection.  For example, a content
   collection could include CMS protection content types as well as
   unprotected content types.  A content collection is expected to be



Housley                                                         [Page 4]

INTERNET DRAFT                                             November 2004


   encapsulated in one or more CMS protecting content types, but this is
   not required by this specification.

   The following object identifier names the content collection content
   type:

      id-ct-contentCollection OBJECT IDENTIFIER ::= {
              iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1)
              pkcs9(9) smime(16) ct(1) 19 }

   The content collection content has the following syntax:

      ContentCollection ::= SEQUENCE SIZE (1..MAX) OF ContentInfo

   The ContentCollection contains a sequence of ContentInfo, one for
   each content in the collection.  The ContentInfo structure is defined
   in CMS.  The contentType object identifier within the ContentInfo
   indicates the type of the associated content.  Implementations of
   this specification SHOULD be prepared to handle object identifiers
   for the SignedData, EncryptedData, EnvelopedData, and
   AuthenticatedData content types as specified in [CMS].
   Implementations of this specification SHOULD also be prepared to
   handle the object identifier for the CompressedData content type as
   specified in [COMPRESS].

3  Content With Attributes Content Type

   The content with attributes content type is used to transfer a single
   content, which is identified by a content type, and a collection of
   attributes associated with that content.  The syntax accommodates an
   arbitrary number of attributes; however, there must be at least one
   attribute.

   The following object identifier names the content with attributes
   content type:

      id-ct-contentWithAttrs OBJECT IDENTIFIER ::= {
              iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1)
              pkcs9(9) smime(16) ct(1) 20 }

   The content with attributes content has the following syntax:

      ContentWithAttributes ::= SEQUENCE {
          content     ContentInfo,
          attrs       SEQUENCE SIZE (1..MAX) OF Attribute }

   The ContentWithAttributes contains a sequence of a single
   ContentInfo, followed by a sequence of attributes.  The ContentInfo



Housley                                                         [Page 5]

INTERNET DRAFT                                             November 2004


   structure is defined in CMS.  The contentType object identifier
   within the ContentInfo indicates the type of the content.  The
   Attribute structure was originally defined in X.501 [X501], and the
   definition is repeated in CMS.

4  References

   This section provides normative and informative references.

4.1  Normative References

   ASN1       CCITT.  Recommendation X.208: Specification of Abstract
              Syntax Notation One (ASN.1).  1988.

   COMPRESS   Gutmann, P.  Compressed Data Content Type for
              Cryptographic Message Syntax (CMS).  RFC 3274.
              June 2002.

   CMS        Housley, R.  Cryptographic Message Syntax.  RFC 3852.
              July 2004.

   STDWORDS   Bradner, S.  Key Words for Use in RFCs to Indicate
              Requirement Levels.  RFC 2119.  March 1997.

4.2  Informative References

   MIME       Freed, N., and N. Borenstein.  Multipurpose Internet Mail
              Extensions (MIME) Part One: Format of Internet Message
              Bodies.  RFC 2045, November 1996.

   X501       CCITT.  Recommendation X.501: The Directory -- Models.
              1988.

5  Security Considerations

   The content collection content type is used to transfer one or more
   contents, each identified by a content type.  The syntax accommodates
   contents with varying levels of protection.  For example, a content
   collection could include CMS protection content types as well as
   unprotected content types.  A content collection is expected to be
   encapsulated in one or more CMS protecting content types, but this is
   not required by this specification.  As a result, implementations
   MUST be prepared to handle multiple levels of encapsulation.

   The security considerations discussed in [CMS] are relevant when CMS
   is used to protect more than one content by making use of the content
   collection content type or content with attributes content type.




Housley                                                         [Page 6]

INTERNET DRAFT                                             November 2004


6  IANA Considerations

   No IANA actions are needed.

7  IPR Considerations

   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.

8  Author's Address

   Russell Housley
   Vigil Security, LLC
   918 Spring Knoll Drive
   Herndon, VA 20170
   USA

   housley@vigilsec.com














Housley                                                         [Page 7]

INTERNET DRAFT                                             November 2004


Appendix A:  ASN.1 Module

   The ASN.1 module contained in this appendix defines the structures
   that are needed to implement this specification.  It is expected to
   be used in conjunction with the ASN.1 modules in [CMS] and
   [COMPRESS].


   ContentCollectionModule
     { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1)
       pkcs-9(9) smime(16) modules(0) 26 }

   DEFINITIONS IMPLICIT TAGS ::=
   BEGIN

   IMPORTS
     Attribute, ContentInfo
       FROM CryptographicMessageSyntax -- [CMS]
         { iso(1) member-body(2) us(840) rsadsi(113549)
           pkcs(1) pkcs-9(9) smime(16) modules(0) cms-2001(14) };


   -- Content Collection Content Type and Object Identifier

   id-ct-contentCollection OBJECT IDENTIFIER ::= {
           iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1)
           pkcs9(9) smime(16) ct(1) 19 }

   ContentCollection ::= SEQUENCE SIZE (1..MAX) OF ContentInfo


   -- Content With Attributes Content Type and Object Identifier

   id-ct-contentWithAttrs OBJECT IDENTIFIER ::= {
           iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1)
           pkcs9(9) smime(16) ct(1) 20 }

   ContentWithAttributes ::= SEQUENCE {
       content     ContentInfo,
       attrs       SEQUENCE SIZE (1..MAX) OF Attribute }

   END









Housley                                                         [Page 8]

INTERNET DRAFT                                             November 2004


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.






































Housley                                                         [Page 9]


Html markup produced by rfcmarkup 1.107, available from http://tools.ietf.org/tools/rfcmarkup/