Certificate Management over CMS (CMC): Transport Protocols
draft-ietf-pkix-cmc-trans-08

PKIX Working Group                                             J. Schaad
Internet-Draft                                   Soaring Hawk Consulting
Expires: September 11, 2008                                     M. Myers
                                               TraceRoute Security, Inc.
                                                          March 10, 2008

       Certificate Management over CMS (CMC): Transport Protocols
                    draft-ietf-pkix-cmc-trans-08.txt

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Abstract

   This document defines a number of transport mechanisms that are used
   to move CMC (Certificate Management over CMS (Cryptographic Message
   Syntax)) 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 (defined in [CMC-STRUCT]).  The transport
   mechanisms described in this document are: HTTP, file, mail and TCP.

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   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 [MUST].

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, Full PKI Request or Full PKI 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 |
                 +---------------------+----------------+
                 | Simple PKI Request  | .p10           |
                 | Full PKI Request    | .crq           |
                 | Simple PKI Response | .p7c           |
                 | Full PKI Response   | .crp           |
                 +---------------------+----------------+

                 File PKI Request/Response Identification

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 [SMIMEV3].
   When using a mail based protocol, MIME wrapping between the layers of
   CMS wrapping is optional.  Note that is different from the standard
   S/MIME (Secure MIME) message.

   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

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   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.

   +--------------+------------------------+------------+--------------+
   | Item         | MIME TYPE              | File       | SMIME-TYPE   |
   |              |                        | Extension  |              |
   +--------------+------------------------+------------+--------------+
   | Simple PKI   | application/pkcs10     | .p10       | N/A          |
   | Request      |                        |            |              |
   | Full PKI     | application/pkcs7-mime | .p7m       | CMC-request  |
   | Request      |                        |            |              |
   | Simple PKI   | application/pkcs7-mime | .p7c       | certs-only   |
   | Response     |                        |            |              |
   | Full PKI     | application/pkcs7-mime | .p7m       | CMC-response |
   | Response     |                        |            |              |
   +--------------+------------------------+------------+--------------+

             Table 1: MIME PKI Request/Response Identification

4.  HTTP/HTTPS based protocol

   This section describes the conventions for use of HTTP [HTTP] as a
   transport layer.  In most circumstances, the use of HTTP over TLS
   [TLS] provides any necessary content protection from ease-droppers.

   In order for CMC clients and servers using HTTP to interoperate, the
   following rules apply.
      Clients MUST use the POST method to submit their requests.
      Servers MUST use the 200 response code for successful reponses.
      Clients MAY attempt to send HTTP requests using TLS 1.0 [TLS] or
      later, although servers are not required to support TLS.
      Servers MUST NOT assume client support for any type of HTTP
      authentication such as cookies, Basic authentication or Digest
      authentication.
      Clients and servers are expected to follow the other rules and
      restrictions in [HTTP].  Note that some of those rules are for
      HTTP methods other than POST; clearly, only the rules that apply
      to POST are relevant for this specification.

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4.1.  PKI Request

   A PKI Request using the POST method is constructed as follows:

   The Content-Type header MUST have the appropriate value from Table 1.

   The body of the message is the binary value of the encoding of the
   PKI Request.

4.2.  PKI Response

   An HTTP-based PKI Response is composed of the appropriate HTTP
   headers, followed by the binary value of the BER (Basic Encoding
   Rules) encoding of either a Simple or Full PKI Response.

   The Content-Type header MUST have the appropriate value from Table 1.

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 client after recieving a final
   response.  If a second round of messages is needed, the client can
   either re-use the same connection or use a new one.

   There is no specific port that is to be used when doing TCP based
   transport.  Only the Private Ports (49152-65535) may be used in this
   manner (without registration).  The ports in the range of (1-49151)
   SHOULD NOT be used.  The port to be used is configured out of band.

6.   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 of [CMC-STRUCT].  Developers of
   state-constrained PKI clients are strongly encouraged to incorporate
   the use of these attributes.

   Initiation of a secure communications channel between an end-entity

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   and a CA or RA (and, similarly, between an RA and another RA or CA)
   necessarily requires an out-of-band trust initiation mechanism.  For
   example, a secure channel may be constructed between the end-entity
   and the CA via IPsec [IPsec] or TLS [TLS].  Many such schemes exist
   and the choice of any particular scheme for trust initiation is
   outside the scope of this document.  Implementers of this protocol
   are strongly encouraged to consider generally accepted principles of
   secure key management when integrating this capability within an
   overall security architecture.

   In some instances no prior out-of-band trust will have been initiated
   prior to use of this protocol.  This can occur when the protocol
   itself is being used to download onto the system the set of trust
   anchors to be used for these protocols.  In these instances the
   Enveloped Data Content type (section 3.2.1.3.3 in [CMC-STRUCT]) must
   be used to provide the same shrouding that TLS would have provided.

7.  IANA Considerations

   There are no IANA considerations in this document.

8.  Acknowledgments

   The authors and the Working Group are grateful for the participation
   of Xiaoui Lui and Jeff Weinstein in helping to author the original
   versions of this document.

   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

9.1.  Normative References

   [CMC-STRUCT]
              Schaad, J. and M. Myers, "Certificate Management Messages
              over CMS", draft-ietf-pkix-2797-bis-05.txt ,
              September 2005.

   [HTTP]     Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
              Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
              Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.

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   [IPsec]    Kent, S. and K. Seo, "Security Architecture for the
              Internet Protocol", RFC 4301, December 2005.

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

   [SMIMEV3]  Ramsdell, B., "Secure/Multipurpose Internet Mail
              Extensions (S/MIME) Version 3.1 Message Specification",
              RFC 3851, July 2004.

9.2.  Informative References

   [TLS]      Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.1", RFC 4346, April 2006.

Authors' Addresses

   Jim Schaad
   Soaring Hawk Consulting
   PO Box 675
   Gold Bar, WA  98251

   Phone: (425) 785-1031
   Email: jimsch@nwlink.com

   Michael Myers
   TraceRoute Security, Inc.

   Email: mmyers@fastq.com

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