PKIX Working Group                                           J. Schaad
Internet Draft                                 Soaring Hawk Consulting
Document: draft-ietf-pkix-cmc-trans-02.txt                     M.Myers
February 2005                                      TraceRoute Security
Expires: July 2005                                               X.Liu
                                                                  Cisco
                                                           J. Weinstein

                             CMC Transport

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   all provisions of Section 10 of RFC2026 [1].

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Copyright Notice

   Copyright (C) The Internet Society (2000).  All Rights Reserved.

Abstract

   This document defines a number of transport mechanisms that are used
   to move [CMC] messages.  The transport mechanisms described in this
   document are: HTTP, file, mail and TCP.


1. Overview

   This document defines a number of transport methods that are used to
   move [CMC] messages.  The transport mechanisms described in this
   document are: HTTP, file, mail and TCP.



   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in
   this document are to be interpreted as described in [RFC 2119].


2. File based protocol

   Enrollment messages and responses may be transferred between clients
   and servers using file system-based mechanisms, such as when
   enrollment is performed for an off-line client.  When files are used
   to transport binary, BER-encoded Full Enrollment Request and
   Response messages, there MUST be only one instance of a request or
   response message in a single file.  The following file type
   extensions SHOULD be used:

   Message Type                   File Extension

   Full PKI Request                 .crq

   Full PKI Response                .crp

3. Mail based protocol

   MIME wrapping is defined for those environments that are MIME
   native.

   The basic mime wrapping in this section is taken from [SMIMEV2] and
   [SMIMEV3].  Simple enrollment requests are encoded using the
   "application/pkcs10" content type.  A file name MUST be included
   either in a content type or a content disposition statement.  The
   extension for the file MUST be ".p10".

   Simple enrollment response messages MUST be encoded as content-type
   "application/pkcs7-mime".  An smime-type parameter MUST be on the
   content-type statement with a value of "certs-only." A file name
   with the ".p7c" extension MUST be specified as part of the content-
   type or content-disposition statement.

   Full enrollment request messages MUST be encoded as content-type
   "application/pkcs7-mime".  The smime-type parameter MUST be included
   with a value of "CMC-enroll".  A file name with the ".p7m" extension
   MUST be specified as part of the content-type or content-disposition
   statement.

   Full enrollment response messages MUST be encoded as content-type
   "application/pkcs7-mime".  The smime-type parameter MUST be included
   with a value of "CMC-response."  A file name with the ".p7m"
   extensions MUST be specified as part of the content-type or content-
   disposition statement.

   MIME TYPE                       File Extension        SMIME-TYPE

   application/pkcs10                .p10                  N/A
   (simple PKI request)

   application/pkcs7-mime            .p7m                  CMC-request


   (full PKI request)

   application/pkcs7-mime            .p7c                  certs-only
   (simple PKI response)

   application/pkcs7-mime            .p7m                  CMC-response
   (full PKI response)

4. HTTP/HTTPS based protocol

   HTTP messages are wrapped with by a mime object as specified above.

5. TCP based protocol

   When CMC messages are sent over a TCP-Based connection, no wrapping
   is required of the message.  Messages are sent in their binary
   encoded form.

   The connection is closed by the server after generating a response
   for the client.  (All CMC request messages from client to server
   generate a response message.)  If a second set of messages from the
   client to the server is required to complete the transaction, the
   client generates a new TCP-Based connection for this purpose; it
   cannot reuse an existing one.

   Out of band setup can be used to keep a TCP-Based connection open
   for more than one message pair.  A situation where this can occur is
   an RA talking to a CA over a specially setup TCP connection.

6  Socket-Based Transport

   When enrollment messages and responses are sent over sockets, no
   wrapping is required.  Messages MUST be sent in their binary, BER-
   encoded form.

7.  Security Considerations

   Mechanisms for thwarting replay attacks may be required in
   particular implementations of this protocol depending on the
   operational environment. In cases where the CA maintains significant
   state information, replay attacks may be detectable without the
   inclusion of the optional nonce mechanisms. Implementers of this
   protocol need to carefully consider environmental conditions before
   choosing whether or not to implement the senderNonce and
   recipientNonce attributes described in section 5.6.  Developers of
   state-constrained PKI clients are strongly encouraged to incorporate
   the use of these attributes.

8. Acknowledgments

   The authors would like to thank Brian LaMacchia for his work in
   developing and writing up many of the concepts presented in this
   document.  The authors would also like to thank Alex Deacon and Barb
   Fox for their contributions.

9. References



   [CMC]      J. Schaad, M. Myers, X. Liu, J. Weinstein, "Certificate
              Management Messages over CMS",
              draft-ietf-pkix-cmc-base-03.txt.

   [RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [SMIMEV2]  Dusse, S., Hoffman, P., Ramsdell, B., Lundblade, L. and
   L.
              Repka, "S/MIME Version 2 Message Specification", RFC
   2311,
              March 1998.

   [SMIMEV3]  Ramsdell, B., "S/MIME Version 3 Message Specification",
              RFC 2633, June 1999.

10. Authors' Addresses

   Jim Schaad
   Soaring Hawk Consulting

   EMail:  jimsch@exmsft.com


   Michael Myers
   TraceRoute Security, Inc.

   EMail: myers@coastside.net


   Xiaoyi Liu
   Cisco Systems
   170 West Tasman Drive
   San Jose, CA 95134

   Phone: (480) 526-7430
   EMail: xliu@cisco.com


   Jeff Weinstein

   EMail: jsw@meer.net



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Acknowledgement

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