Movatterモバイル変換

Network Working Group                                        R. HousleyRequest for Comments: 4073                               Vigil SecurityCategory: Standards Track                                      May 2005Protecting Multiple Contents with theCryptographic 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 (2005).Abstract   This document describes a convention for using the Cryptographic   Message Syntax (CMS) to protect a content collection.  If desired,   attributes can be associated with the content.1.  Introduction   This document describes a convention for using the Cryptographic   Message Syntax (CMS) [CMS] to protect a content collection.  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.   The convention described in this document is not needed when CMS is   used with MIME [MSG].  MIME multipart [MIME] provides a   straightforward and widely deployed mechanism for carrying more than   one content item, each associated with a MIME type.   However, 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 item,   each with an object identifier to specify the content type.   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].Housley                     Standards Track                     [Page 1]

RFC 4073       Protecting Multiple Contents with the CMS        May 20051.1.  Content Collection Example   This section provides one simple example to illustrate 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.   +---------------------------------------------------------+   |                                                         |   | 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 TypeHousley                     Standards Track                     [Page 2]

RFC 4073       Protecting Multiple Contents with the CMS        May 20051.2.  Content with Attributes Example   This section provides one simple example to illustrate the need for   the content-with-attributes content type.  Consider the art collector   from 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 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 TypeHousley                     Standards Track                     [Page 3]

RFC 4073       Protecting Multiple Contents with the CMS        May 20052.  Content Collection Content Type   The content-collection content type is used to transfer a collection   of content items, 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.   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 }Housley                     Standards Track                     [Page 4]

RFC 4073       Protecting Multiple Contents with the CMS        May 2005   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   item followed by a sequence of attributes.  The ContentInfo 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.  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.5.  References5.1.  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 (CMS)",RFC3852, July 2004.   [STDWORDS]  Bradner, S., "Key words for use in RFCs to Indicate               Requirement Levels",BCP 14,RFC 2119, March 1997.Housley                     Standards Track                     [Page 5]

RFC 4073       Protecting Multiple Contents with the CMS        May 20055.2.  Informative References   [MIME]      Freed, N. and N. Borenstein, "Multipurpose Internet Mail               Extensions (MIME) Part One: Format of Internet Message               Bodies",RFC 2045, November 1996.   [MSG]       Ramsdell, B., "Secure/Multipurpose Internet Mail               Extensions (S/MIME) Version 3.1 Message Specification",RFC 3851, July 2004.   [X501]      CCITT.  Recommendation X.501: The Directory -- Models.               1988.Housley                     Standards Track                     [Page 6]

RFC 4073       Protecting Multiple Contents with the CMS        May 2005Appendix 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 CryptographicMessageSyntax2004 -- [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 }   ENDHousley                     Standards Track                     [Page 7]

RFC 4073       Protecting Multiple Contents with the CMS        May 2005Author's Address   Russell Housley   Vigil Security, LLC   918 Spring Knoll Drive   Herndon, VA 20170   USA   EMail: housley@vigilsec.comHousley                     Standards Track                     [Page 8]

RFC 4073       Protecting Multiple Contents with the CMS        May 2005Full Copyright Statement   Copyright (C) The Internet Society (2005).   This document is subject to the rights, licenses and restrictions   contained inBCP 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 inBCP 78 andBCP 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 athttp://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 9]