Internet Draft                              Ronald Tschalar (Trustpoint)
PKIX Working Group                              Amit Kapoor (Trustpoint)
Expires in 6 months                          Carlisle Adams (Entrust)

                                                               Sep. 1999


                  Using TCP as a Transport Protocol for CMP
                      <draft-ietf-pkix-cmp-tcp-00.txt>


Status of this Memo

  This document is an Internet-Draft and is in full conformance with
  all provisions of Section 10 of RFC2026.

  Internet-Drafts are working documents of the Internet Engineering
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  This Internet-Draft will expire on February 2, 2000


Copyright Notice

  Copyright (C)The Internet Society (1999). All Rights Reserved.


Abstract

  This document describes how to layer Certificate Management
  Protocols [CMP] over [TCP]. A method for doing so is described in
  section 5.2 of [CMP], but that method does not solve problems
  encountered by implementors. This document specifies an enhanced
  method which extends the protocol.

  The key words "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT",
  "RECOMMENDED", "MAY", and "OPTIONAL" in this document (in uppercase,
  as shown) are to be interpreted as described in [RFC2119].


. Motivation

  Section 5.2 of the CMP spec specifies sending the DER-encoded CMP
  message directly over TCP. However, implementors, during various
  interoperability workshops, found the protocol lacking in the
  following respects:

  1.    No clear definition on when the connection is to be closed
        and by whom.
  2.    No version number specified to allow for extensions.
  3.    Error messages cannot be processed by applications.

  Realizing that this could not be achieved in a backward compatible
  way, the decision was made to enhance the protocol now to avoid
  interoperability conflicts later. This enhancement tries to keep
  as much of the older protocol as possible, while ensuring that
  implementations using the old protocol will not mistake a TCP-Message
  (defined in Section 2.1) for a valid message in the RFC-2510 format.


. TCP-Based Management Protocol

   The following simple TCP-based protocol is to be used for transport
   of PKI messages. This protocol is suitable for cases where an end
   entity (or an RA) initiates a transaction and can poll to pick up the
   results.

   The client sends a TCP-message to the server, and the server responds
   with another TCP-message.

   The protocol basically assumes a listener process on an RA or CA
   which can accept TCP-messages on a well-defined port (default port number
   is 829). Typically a client initiates connection to the server and
   submits a PKI message. The server replies with a PKI message or with
   a reference number to be used later when polling for the actual PKI
   message response.

   If a polling-reference was supplied then the client will send
   a polling request using this polling-reference after waiting for at
   least the specified time. The server may again reply with a
   polling-reference or with the actual PKI message response.

   When the final PKI response message has been picked up by the
   client then no new polling reference is supplied.

   If a transaction is initiated by a PKI entity (RA or CA) then an end
   entity must either supply a listener process or be supplied with a
   polling reference (see below) in order to allow it to pick up the PKI
   message from the PKI management component.

2.1 General Form

   A TCP-message consists of:

         length (32-bits)
         version (8-bits)
         flags (variable length)
         message-type (8-bits),
         value (defined below)

   The length field contains the number of octets of the remainder of
   the TCP-message (i.e., number of octets of <value> plus <flags-length>
   plus 2).  All bit values in this protocol are specified to be in
   network byte order.

   The version field indicates the version of the TCP-message. It MUST
   be incremented for each specification which changes the flags field
   in a way that is not fully backwards compatible with the previous
   version (e.g. when the length of the flags field is changed), or
   which introduces a new message-type.

   The flags field is for transporting TCP-message specific data. The
   length of this field is version dependent and is fixed for a given
   version.

   The message-type field is used to indicate the type of TCP-message.

   The value field contains message-type dependent data.

2.2 Version Negotiation

   If a client knows the protocol version(s) supported by the
   server (e.g. from a previous TCP-message exchange or via some
   out-of-band means) then it SHOULD send a TCP-message with the highest
   version supported both by it and the server. If a client does
   not know what version(s) the server supports then it SHOULD send
   a TCP-message using the highest version it supports.

   If a server receives a TCP-message version that it supports, then it
   MUST reply with a TCP-message of the same version. If the version
   received is higher than what the server supports, it MUST send
   back a VersionNotSupported errorMsgRep (defined below) containing
   the highest version it supports.

2.3 TCP-message Version 10

   The TCP-message version will be 10 for this document. The number has
   deliberately been chosen to prevent RFC-2510 compliant applications
   from treating it as a valid message type. Applications receiving a
   version less than 10 SHOULD interpret the message as being an
   RFC-2510 style message.

   The length of the flags field for this version is 1 octet. The LSB
   is used to indicate a connection close; all other bits in the flags
   octet MUST be ignored by servers, and MUST be set to zero by
   senders.

   By default connections are kept open after the receipt of a
   response. Either party (client or server) MAY set the connection
   close bit at any time.  If the connection close bit is set on a request,
   then the server SHOULD set the bit in the response and close the
   connection after sending the response. If the bit is set on a
   response from the server, the client MUST NOT send any
   further requests on that connection. Applications MAY decide to
   close an idle connection (one on which no response is outstanding)
   after some time-out. Because of the problem where a client sends
   a request and the server closes the connection while the request
   is still in flight, clients SHOULD automatically retry a request
   for which no part of the response could be read due to a connection
   close or reset.

   If the connection is kept open, it MUST only be used for subsequent
   request/response transactions started by the client - the server
   MUST NOT use it to send requests to the client.

2.4 Detecting and Interoperating with RFC-2510 Conformant Implementations

   Servers wishing to interoperate with clients conforming to RFC-2510
   can do so by treating any received message with a version less than
   10 as an RFC-2510 message and responding in that format.  Servers
   not wishing to support RFC-2510 messages MUST respond with a RFC-2510
   errorMsgRep.

   Clients wishing to interoperate with RFC-2510 compliant servers
   SHOULD treat a response with a version less than 10 as an RFC-2510
   style message. If this message is an errorMsgRep (message-type
   06) then the client MAY automatically retry the request using the
   RFC-2510 format; if the message is not an errorMsgRep or the implementation
   does not wish to support RFC-2510 then it MUST abort the corresponding CMP
   transaction.

2.5 Message Types

   message-types 0-127 are reserved and will be issued under IANA
   auspices. message-types 128-255 are reserved for application use.

   The message-type's currently defined are:

    Message name            Message-type

    pkiReq                  '00'H

    pollRep                 '01'H

    pollReq                 '02'H

    finRep                  '03'H

    pkiRep                  '05'H

    errorMsgRep             '06'H

   The different TCP-messages are discussed in the following sections:

2.5.1 pkiReq

   The pkiReq is to be used to carry a PKIMessage from the client to the
   server.  The <value> portion of this TCP-message will contain:

           DER-encoded PKIMessage.

   The type of PKIMessages that can be carried by this TCP-message are:

           Initialization Request
           Certification Request
           PKCS-10 Request
           POP Response
           Key Update Request
           Key Recovery Request
           Revocation Request
           Cross-Certification Request
           CA Key Update Announcement
           CRL Announcement
           Certificate Announcement
           Confirmation
           Nested Message
           General Message
           Error Message

2.5.2 pkiRep

   This TCP-message is to be used to send back the response to the request.
   The <value> portion of the finalMsgRep will contain:

           DER encoded PKI message

   The type of PKIMessages that can be carried by this TCP-message are:

           Initialization Response
           Certification Response
           POP Request
           Key Update Response
           Key Recovery Response
           Revocation Response
           General Response
           Error Message

2.5.3 pollReq

   The pollReq will be the used by the client to check the status of
   a pending PKI message.  The <value> portion of the pollReq will contain:

           polling-reference (32 bits)

   The <polling-reference> MUST be the one returned via the pollRep TCP-message.

2.5.4 pollRep

   The pollRep will be the response sent by the server to the client
   when there are no PKI message response ready.  The <value> portion of
   the pollRep will contain:

           polling-reference (32 bits)
           time-to-check-back (32 bits)

   The <polling-reference> is a unique 32-bit number sent by the server.
   The <time-to-check-back> is the time in seconds indicating the minimum
   interval after which the client SHOULD check the status again.

   The duration for which the server keeps the <polling-reference>
   unique is left to the implementation.

2.5.5 finRep

    finRep will be the response from the server indicating end of
    transaction, i.e., there are no further messages to be delivered
    from the server.  The <value> portion of the finRep will
    contain:

           '00'H (8 bits)

2.5.6 errorMsgRep

   This TCP-message is sent when a TCP-message level protocol error is
   detected. Please note that PKIError messages MUST NOT be sent
   using this. Examples of TCP-message level errors are:

   1.  Invalid protocol version
   2.  Invalid TCP message-type
   3.  Invalid polling reference number

   The <value> field of the TCP-message SHALL contain:

            error-type (16-bits)
            data-length (16-bits)
            data (<data-length> octets)
            UTF8 String (SHOULD include a RFC 1766 language tag)

   The <error-type> is of the form MMNN where M and N are hex digits
   [0-F] and MM represents the major category and NN the minor. The
   major categories defined by this specification are:

     '01'H   TCP-message version negotiation
     '02'H   client errors
     '03'H   server errors

   The <data-length> and <data> are additional information about the
   error to be used by programs for further processing and recovery.
   <data-length> contains the length of the <data> field in number of
   octets. Error messages not needing additional information to be
   conveyed should set the <data-length> to 0.

   The UTF8 text string is for user readable error messages.

2.5.6.1 VersionNotSupported errorMsgRep

   The VersionNotSupported errorMsgRep is defined as follows:

      error-type:                        '0101'H
      data-length:                             1
      data:                            <version>
      UTF8-text String:   implementation defined

   where <version> is the highest version the server supports.

2.5.6.2 GeneralClientError errorMsgRep

   The GeneralClientError errorMsgRep is defined as follows:

      error-type:                        '0200'H
      data-length:                             0
      data:                              <empty>
      UTF8-text String:   implementation defined

2.5.6.3 MessageTypeUnknown errorMsgRep

   The MessageTypeUnknown errorMsgRep is defined as follows:

      error-type:                        '0201'H
      data-length:                             1
      data:                       <message-type>
      UTF8-text String:   implementation defined

   where <message-type> is the message-type received by the
   server.

2.5.6.4 InvalidPollID errorMsgRep

   The InvalidPollID errorMsgRep is defined as follows:

      error-type:                        '0202'H
      data-length:                             4
      data:                  <polling-reference>
      UTF8-text String:   implementation defined

   where <polling-reference> is the polling-reference received by
   the server.

. CMP over TCP

  The following sections describe how the above protocol is to be
  used to carry the PKI messages.  Similar behaviour has been
  put in the same section.

3.1 Initialization/Certificate/Key Update/Key Recovery/Revocation

  These requests MUST be sent using the pkiReq message-type. In response,
  the server SHOULD send back one of the following:

    1.  errorMsgRep
    2.  pollRep
    3.  pkiRep

  Any other TCP-message is to be treated as an error.

  On receiving the pollRep, the client SHOULD use the delta time
  specified in the pollRep to check the status, using pollReq.

  The final PKI message in the transaction MUST be sent in pkiRep from
  the server to the client.  The client MUST send the
  PKIConfirm in pkiReq, and on successful processing SHOULD get back
  a finRep indicating an end of the transaction.

3.2 Cross Certification/General Message

  These requests MUST be sent using the pkiReq message-type. In response,
  the server SHOULD send back one of the following:

    1.  errorMsgRep
    2.  pollRep
    3.  pkiRep

  Any other TCP-message is to be treated as an error.

  On receiving the pollRep, the client SHOULD use the delta time
  specified in the pollRep to check the status later, using pollReq.
  It is RECOMMENDED, however, that the server process the PKI message
  immediately and return the PKI response (i.e. instead of sending a
  pollRep).

  The server MUST send back the Cross Certification response/
  General response in a pkiRep.

3.3 CA Key Update/Certificate Ann/ Revocation Ann/CRL Ann

  These requests MUST be sent using the pkiReq message-type. In response,
  the server SHOULD send back one of the following:

    1.  errorMsgRep
    2.  pollRep
    3.  pkiRep

  Any other TCP-message is to be treated as an error.

  The server MUST send the pkiRep only if it contains a PKIError message.
  Successful processing of the request MUST result in a finRep.


. Security Considerations

  No new security considerations with respect to [CMP] are introduced.


. Acknowledgments

   The following individuals also deserve credit for their review and
   input:

      Robert Moskowitz, ICSA;
      Keith Brady, Baltimore;
      Ron Chittaro, Entrust;
      Mike Shanzer, Iris Associates;
      John Wray, Iris Associates;


. References

  [CMP]     Adams, C., Farrell, S., "Internet X.509 Public Key
            Infrastructure, Certificate Management Protocols", RFC 2510,
            March 1999.

  [HTTP]    Fielding, R.T., et. al, "Hypertext Transfer Protocol --
            HTTP/1.1", RFC 2616, June 1999.

  [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", RFC 2119, March 1997.

  [RFC821]  Postel, J., "Simple Mail Transfer Protocol", RFC 821,
            August 1982.


Authors' Addresses

  Amit Kapoor
  Trustpoint
  429 Castro Street, Suite B
  Mountain View, CA 94041
  US

  E-Mail: amit@trustpoint.com

  Ronald Tschal„r
  Trustpoint
  429 Castro Street, Suite B
  Mountain View, CA 94041
  US

  E-Mail: ronald@trustpoint.com

  Carlisle Adams
  Entrust Technologies
  750 Heron Road, Suite E08,
  Ottawa, Ontario
  Canada K1V 1A7

  EMail: cadams@entrust.com


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