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Network Working Group                                           T. Kause
Internet-Draft                                                       SSH
Updates: 4210 (if approved)                                     M. Peylo
Intended status: Standards Track                                     NSN
Expires: April 2, 2011                                September 29, 2010


Internet X.509 Public Key Infrastructure -- Transport Protocols for CMP
             draft-ietf-pkix-cmp-transport-protocols-10.txt

Abstract

   This document describes how to layer the Certificate Management
   Protocol over various transport protocols.  It is the "CMPtrans"
   document referenced in RFC 4210 and therefore updates the reference
   given therein.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   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 as "work in progress."

   This Internet-Draft will expire on April 2, 2011.

Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.



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   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may
   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Requirements . . . . . . . . . . . . . . . . . . . . . . . . .  5
   3.  HTTP-Based Protocol  . . . . . . . . . . . . . . . . . . . . .  6
     3.1.  HTTP Versions  . . . . . . . . . . . . . . . . . . . . . .  6
     3.2.  Persistent Connections . . . . . . . . . . . . . . . . . .  6
     3.3.  General Form . . . . . . . . . . . . . . . . . . . . . . .  6
     3.4.  Media Type . . . . . . . . . . . . . . . . . . . . . . . .  7
     3.5.  Communication Workflow . . . . . . . . . . . . . . . . . .  7
     3.6.  HTTP Request-URI . . . . . . . . . . . . . . . . . . . . .  7
     3.7.  Announcements  . . . . . . . . . . . . . . . . . . . . . .  8
       3.7.1.  Pushing of Announcements . . . . . . . . . . . . . . .  8
       3.7.2.  Polling of Announcements . . . . . . . . . . . . . . .  9
         3.7.2.1.  CA Key Update Announcement . . . . . . . . . . . .  9
         3.7.2.2.  Revocation Announcement  . . . . . . . . . . . . . 10
         3.7.2.3.  CRL Announcement . . . . . . . . . . . . . . . . . 10
     3.8.  HTTP Considerations  . . . . . . . . . . . . . . . . . . . 11
     3.9.  Compatibility Issues with Legacy Implementations . . . . . 11
   4.  TCP-Based Management Protocol  . . . . . . . . . . . . . . . . 12
     4.1.  General Form . . . . . . . . . . . . . . . . . . . . . . . 12
     4.2.  Version  . . . . . . . . . . . . . . . . . . . . . . . . . 13
       4.2.1.  Version Negotiation  . . . . . . . . . . . . . . . . . 13
       4.2.2.  Detection and Interoperation with RFC2510
               Conformant Implementations . . . . . . . . . . . . . . 14
     4.3.  Flags  . . . . . . . . . . . . . . . . . . . . . . . . . . 14
       4.3.1.  Connection Close Flag  . . . . . . . . . . . . . . . . 14
     4.4.  Message-Types  . . . . . . . . . . . . . . . . . . . . . . 15
       4.4.1.  pkiReq . . . . . . . . . . . . . . . . . . . . . . . . 15
       4.4.2.  pkiRep . . . . . . . . . . . . . . . . . . . . . . . . 16
       4.4.3.  pollReq  . . . . . . . . . . . . . . . . . . . . . . . 16
       4.4.4.  pollRep  . . . . . . . . . . . . . . . . . . . . . . . 17
       4.4.5.  finRep . . . . . . . . . . . . . . . . . . . . . . . . 17
       4.4.6.  errorMsgRep  . . . . . . . . . . . . . . . . . . . . . 17
         4.4.6.1.  VersionNotSupported  . . . . . . . . . . . . . . . 18



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         4.4.6.2.  GeneralClientError . . . . . . . . . . . . . . . . 19
         4.4.6.3.  InvalidMessageType . . . . . . . . . . . . . . . . 19
         4.4.6.4.  InvalidPollID  . . . . . . . . . . . . . . . . . . 20
         4.4.6.5.  GeneralServerError . . . . . . . . . . . . . . . . 20
   5.  File-Based Protocol  . . . . . . . . . . . . . . . . . . . . . 21
   6.  Mail-Based Protocol  . . . . . . . . . . . . . . . . . . . . . 22
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 23
   8.  Information Security Considerations  . . . . . . . . . . . . . 24
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 25
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 26
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 26
     10.2. Informative References . . . . . . . . . . . . . . . . . . 26
   Appendix A.  Acknowledgments . . . . . . . . . . . . . . . . . . . 27
   Appendix B.  Registration of the application/pkixcmp Media Type  . 28
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 30




































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1.  Introduction

   The Certificate Management Protocol (CMP) [RFC4210] requires well
   defined transport mechanisms to enable End Entities, RAs and CAs to
   pass PKIMessage sequences between them.  This document defines the
   transport mechanisms which were removed from the main CMP
   specification with the second release and referred to be in a
   separate document.

   The first version of the CMP specification [RFC2510] included a brief
   description of a simple TCP-based transport protocol.  Its features
   are simple transport level error-handling and a mechanism to poll for
   outstanding PKI messages.  Additionally, it was mentioned that PKI
   messages could also be conveyed using file-, E-mail- and HTTP-based
   transport.

   The current version of the CMP specification incorporated an own
   polling mechanism and thus the need for a transport protocol
   providing this functionality vanished.  The remaining features CMP
   requires from its transport protocols are connection- and error-
   handling.

   During the long time it existed as draft, this RFC was undergoing
   drastic changes.  The TCP-based transport specification was enhanced
   and a TCP-Messages-over-HTTP transport specification appeared.  Both
   proved to be needless and cumbersome, implementers preferred to use
   plain HTTP transport.  This specification now aims to reflect that.

   HTTP transport is generally easy to implement, traverses network
   borders utilizing ubiquitous proxies and is already commonly found in
   existing implementations.  TCP-based transport is only documented for
   information and optional downward compatibility.  E-Mail or file
   transfer are also mentioned and may be used to convey PKIMessage
   sequences - provided that scenarios are identified where they are
   better suited than HTTP.
















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2.  Requirements

   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 [RFC2119].














































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3.  HTTP-Based Protocol

   For direct interaction between two entities, where a reliable
   transport protocol like TCP is available, HTTP SHOULD be utilized for
   conveying CMP messages.

   With its status codes, HTTP provides needed error reporting
   capabilities.  General problems on the server side as well as those
   directly caused by the respective request can be reported to the
   client.

   As CMP implements a transaction ID, identifying transactions
   consisting of more than just a single request/response pair, the
   statelessness of HTTP is not blocking its usage as transport protocol
   for CMP messages.

3.1.  HTTP Versions

   Either HTTP/1.0 as described in [RFC1945] or HTTP/1.1 as in [RFC2616]
   MAY be used.  Naturally, the newer version should be preferred.  To
   support legacy implementations, both server and client MUST be able
   to interact with counterparts utilizing the other HTTP protocol
   version.

3.2.  Persistent Connections

   HTTP permits to reuse a connection for subsequent requests.
   Implementations may use this functionality for messages within the
   same transaction but MUST NOT rely on that, as e.g. intermediate HTTP
   proxies might terminate the connection after each request/response
   pair.

   In contrast to HTTP/1.1, persistent connections are explicitly
   negotiated in HTTP/1.0.  To avoid the problems described in chapter
   19.6.2 in [RFC2616], HTTP/1.0 implementations must not send Keep-
   Alive when talking to proxies.

3.3.  General Form

   An ASN.1 DER-encoded PKIMessage is sent as the entity-body of an HTTP
   POST request.  If this HTTP request is successful, the server returns
   the CMP reply in the body of the HTTP response.  The response status
   code in this case MUST be 200; other 2xx codes MUST NOT be used for
   this purpose.  The HTTP responses with empty message body to CMP
   Announcement messages also utilize the status codes 201 and 202 to
   identify if the information was properly processed.

   Note that a server may return any 1xx, 3xx, 4xx, or 5xx status code



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   if the HTTP request needs further handling or is otherwise not
   acceptable.

3.4.  Media Type

   The Internet Media Type "application/pkixcmp" MUST be set in the HTTP
   header when conveying a PKIMessage.

3.5.  Communication Workflow

   In CMP most communication is initiated by the end entities where
   every CMP request triggers a CMP response message from the CA or RA.

   The CMP Announcement messages described in Section 3.7 are an
   exception.  Their creation may be triggered by events or generated on
   a regular basis by a CA.  The recipient of the Announcement only
   replies with an HTTP status code acknowledging the receipt or
   indicating an error but not with a CMP response.

   The receipt of every HTTP message is confirmed by the counterpart
   using HTTP means or it MUST be assumed by the sender that it was not
   successfully delivered to its destination.

3.6.  HTTP Request-URI

   The Request-URI is formed as specified in [RFC3986].

   Client requests containing a PKI message MUST be directed to an
   Request-URI depicting a directory.  A server implementation MUST
   handle Request-URIs with or without a trailing slash as identical.
   The following list contains all such CMP message types.  The prefixed
   numbers reflect ASN.1 numbering of the respective element.

      [0] Initialization Request
      [2] Certification Request
      [4] PKCS-10 Request
      [6] pop Response
      [7] Key Update Request
      [9] Key Recovery Request
      [11] Revocation Request
      [13] Cross-Certification Request
      [15] CA Key Update Announcement
      [16] Certificate Announcement
      [17] Revocation Announcement
      [18] CRL Announcement
      [20] Nested Message





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      [21] General Message
      [23] Error Message
      [24] Certificate Confirmation
      [25] Polling Request

   An example of a Request-Line and a Host header field in an HTTP/1.1
   header, sending a CMP request to a server, located in the "/cmp"
   directory of the host example.com, would be

      POST /cmp HTTP/1.1
      Host: example.com

   or in the absoluteURI form

      POST http://example.com/cmp/ HTTP/1.1
      Host: example.com

   A CMP server may be logically located either inside the root- or
   within subdirectories of an HTTP server.  As default, the path should
   end in a "cmp" directory.

3.7.  Announcements

   A CMP server may create event-triggered announcements or generate
   them on a regular basis.  It MAY also utilize HTTP transport to
   convey them to a suitable recipient.  They can either be pushed to
   the recipient or polled from the HTTP CMP server.

3.7.1.  Pushing of Announcements

   The ASN.1 encoded structures are sent as the entity-body of an HTTP
   POST request.

   Suitable recipients for CMP announcements might e.g. be repositories
   storing the announced information such as directory services.  Those
   listen for incoming messages, utilizing the same HTTP Request-URI
   scheme as defined in Section 3.6.

   The following PKIMessages are announcements that may be pushed by a
   CA.  The prefixed numbers reflect ASN.1 numbering of the respective
   element.

      [15] CA Key Update Announcement
      [16] Certificate Announcement
      [17] Revocation Announcement
      [18] CRL Announcement

   CMP announcement messages do not require any CMP response.  However,



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   the recipient MUST acknowledge receipt with a HTTP message having an
   appropriate status code and an empty body.  The sending side should
   assume the delivery unsuccessful without such reply and retry if
   applicable after waiting for an appropriate time span.

   If the announced issue was successfully stored in a database or was
   already present, the answer MUST be an HTTP message with a "201
   Created" status code and empty message body.

   In case the announced issue was only stored for further processing,
   the status code of the returned HTTP message must be "202 Accepted".
   After an appropriate delay, the server may then try to send the
   Announcement again and may repeat this until it receives a
   confirmation that it had been successfully stored.  The appropriate
   duration of the delay and the option to increase it between
   consecutive attempts should be carefully considered.

   A receiver MUST answer with a suitable 4xx or 5xx HTTP error code
   when a problem occurs.

3.7.2.  Polling of Announcements

   As an OPTIONAL feature a CA may provide CA Key Update Announcement,
   Revocation Announcement and CRL Announcement messages for polling
   using HTTP GET requests.

   The server replies with the requested Announcement as the body of a
   HTTP response having a 200 status code.  If no suitable announcement
   message is available, an HTTP "404 Not Found" error code MUST be
   returned.

   Query components are formed according to [RFC3986].  Their start is
   indicated by the first question mark in the Request-URI and they are
   containing "key=value" pairs.  Hexadecimal representations of ASN.1
   strings used as value MAY contain lower or upper case letters and are
   neither grouped nor prefixed.

   The given examples are for a self-signed certificate with the common
   name (OID 2.5.4.3) "Example CA", the keyIdentifier in hexadecimal
   representation BE911E711EDB685BF94D9B176A1BC715CE51D794 and the
   serial number 008F8B7E383D88327C.

3.7.2.1.  CA Key Update Announcement

   When updating its key pair, a CA can produce a CA Key Update
   Announcement Message that can be made available to the relevant end
   entities.  This is described as "Root CA Key Update" in E.4 of
   [RFC4210].



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   A CMP server may provide this message via an HTTP GET request for the
   CAKeyUpdAnn.PKI file in the respective server's path.  The
   identification of the old key in question is created according to the
   Authority Key Identifier as defined in chapter 4.2.1.1 of [RFC5280].
   The query component then cosists of one single "key=value" pair,
   having the string "AuthorityKeyIdentifier" as key, and the
   hexadecimal representation of the ASN.1 AuthorityKeyIdentifier
   sequence as value.

   An example of the query component, when requesting a CA Key Update
   Announcement Message for an old key identified with the
   AuthorityKeyIdentifier 303C8014BE911E711EDB685BF94D9B176A1BC715CE51D7
   94A119A4173015311330110603550403130A4578616D706C652043418209008F8B7E3
   83D88327C

      ?AuthorityKeyIdentifier=303C8014BE911E711EDB685BF94D9B176A1BC715CE
      51D794A119A4173015311330110603550403130A4578616D706C65204341820900
      8F8B7E383D88327C

3.7.2.2.  Revocation Announcement

   A CMP server MAY permit subjects to poll for a Revocation
   Announcement using HTTP means.  This enables a subject to determine
   if its certificate is about to be (or has been) revoked.

   The Request-URI of the HTTP GET targets the RevAnn.PKI file in the
   respective server's path.  The query component contains two
   "key=value" pairs identifying the certificate in question:
   o  an "issuer" key with the hexadecimal representation of the
      certificate's issuer's GeneralNames ASN.1 sequence as value
   o  a "serialNumber" key with the hexadecimal representation of the
      certificate's serial number

   An example of the query component, when requesting a Revocation
   Announcement of a certificate issued by "Example CA" having the
   decimal serialNumber 6699 would be:

      ?issuer=3015311330110603550403130A4578616D706C65204341&
      serialNumber=1A2B


3.7.2.3.  CRL Announcement

   A CMP server MAY offer the possibility to poll for the latest CRL
   Announcement of a specific CA.

   The Request-URI targets the CRLAnn.PKI file.  The query component
   consists of one one "key=value" pair containing an "issuer" key with



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   the hexadecimal representation of the CA's GeneralNames' ASN.1
   sequence as value.

   An example of a Request-URI for the latest CRL Announcement of
   "Example CA" from a CMP server located in the "/cmp" directory of the
   host example.com would be

      http://example.com/cmp/
      CRLAnn.PKI?issuer=3015311330110603550403130A4578616D706C65204341

3.8.  HTTP Considerations

   In general, CMP messages are not cachable; requests and responses
   MUST include a "Cache-Control: no-cache" (and, if either side uses
   HTTP/1.0, a "Pragma: no-cache") to prevent the client from getting
   cached responses.

   Connection management is based on the HTTP provided mechanisms
   (Connection and Proxy-Connection header fields).

   While an implementation MAY make use of all defined features of the
   HTTP protocol, it SHOULD keep the protocol utilization as simple as
   possible.

   There is no need for the clients to send an Expect request-header
   field with the "100-continue" expectation and wait for a 100
   (Continue) status as described in chapter 8.2.3 of [RFC2616].  The
   CMP payload sent by a client is relatively small, so having extra
   messages exchanged is more inefficient as the server will anyway only
   seldomly reject the message without looking at the body.

   Content codings MAY be applied.

3.9.  Compatibility Issues with Legacy Implementations

   As this document was subject of multiple changes during the long
   period of time it was created in, implementations using a different
   approach for HTTP transport may exist.  While only those
   implementations according to this specification are compliant,
   implementers should to be aware that there might be existing ones
   which behave differently.

   Legacy implementations might also use an unregistered "application/
   pkixcmp-poll" MIME type as it was specified in earlier drafts of this
   document.  Here, the entity-body of an HTTP POST request contains a
   TCP-Message instead of a plain DER-encoded PKIMessage.  Effectively,
   this is conveying PKIMessage over TCP-Message over HTTP.




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4.  TCP-Based Management Protocol

   The so-called "TCP-based transport" is OPTIONAL and its use is
   deprecated.  Its description appears here only for information and
   downward compatibility.  HTTP-based transport, as described in
   Section 3, should be preferred when transporting CMP messages as
   defined in [RFC4210].  The reasoning for that is given in Section 1.

   While this section is called TCP-based and the messages are called
   TCP-Messages, the same protocol can be used over any reliable,
   connection oriented transport protocol (e.g.  SNA, DECnet, etc.).
   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.  A response MUST be sent for every request,
   even if the encapsulated CMP message in the request does not have a
   corresponding response.

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

   If a polling-reference was supplied, the client SHOULD send a polling
   request using this polling-reference after waiting for at least the
   time specified along with the reference number.  The server may again
   reply with a new polling-reference or with the actual CMP message
   response.

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

4.1.  General Form

   The format of a TCP-Message is shown below:













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      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                            Length                             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |  Version = 10 |     Flags     |  Message-Type |               \
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+               /
     \                                                               \
     /                     Value (variable length)                   /
     \                                                               \
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Length: 32 bits (unsigned integer)
       This field contains the number of remaining octets of the TCP-
       Message (i.e. number of octets of the Value field plus 3).  All
       bit values in this protocol are specified to be in network byte
       order.

   Version: 8-bits (unsigned integer)
       The version of the TCP-Message is 10 in for this document.  It
       MUST be incremented in each future specification modification
       e.g. changing the Flags field in a way that is not fully
       backwards compatible.

   Flags: 8 bits
       TCP-Message specific flags as described in Section 4.3.

   Message-Type: 8 bits
       A value indicating the type of the TCP-Message.

   Value: variable length
       Message-type dependent data is stored here.  The usage of this
       field is described along with the respective message-type

4.2.  Version

   The TCP-Message version is 10 for this document.  The number has
   deliberately been chosen to prevent [RFC2510] compliant applications
   from treating it as a valid message type.  Applications receiving a
   version less than 10 SHOULD interpret the message as being an
   [RFC2510] style message.

4.2.1.  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



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   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 containing the highest version it
   supports, see Section 4.4.6.

4.2.2.  Detection and Interoperation with RFC2510 Conformant
        Implementations

   Servers wishing to interoperate with clients conforming to [RFC2510]
   can do so by treating any received message with a version less than
   10 as an [RFC2510] message and responding in that format.  Servers
   not wishing to support [RFC2510] messages MUST respond with a
   [RFC2510] errorMsgRep.

   If a client receives a [RFC2510] errorMsgRep (message-type 06)
   message, it MAY automatically resend the same request on the same
   connection, falling back to the [RFC2510] format; if the received
   message is not an errorMsgRep, it MUST terminate the connection.  It
   MAY then retry the communication falling back completely to the
   [RFC2510] format.

   Naturally, a client MUST abort the connection attempt if the server
   does not support any of the client's supported versions.  It SHOULD
   retry the version negotiation after a delay to check if the server
   was updated.

4.3.  Flags

   The LSB of the Flags field is used to indicate a connection close;
   all other bits in the Flags octet MUST be ignored by receivers, and
   MUST be set to zero by senders.

4.3.1.  Connection Close Flag

   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 MUST 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



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   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.  Different transactions
   may be freely interwoven on the same connection.  E.g. a CR/CP need
   not immediately be followed by the Confirm, but may be followed by
   any other request from a different transaction.

4.4.  Message-Types

   Message-Types 0-127 are reserved and are to be issued under IANA
   auspices.  Message-types 128-255 are reserved for application use.

   The Message-Types currently defined are:

     ID Value   Message Name
     --------   ------------
      '00'H      pkiReq
      '01'H      pollRep
      '02'H      pollReq
      '03'H      finRep
      '05'H      pkiRep
      '06'H      errorMsgRep

   If a server receives an unknown message-type, it MUST reply with an
   InvalidMessageType errorMsgRep.  If a client receives an unknown
   message-type, it MUST abort the current CMP transaction and terminate
   the connection.

   The different TCP-Message-types are discussed in the following
   sections:

4.4.1.  pkiReq

   A pkiReq message conveys a PKIMessage from a client to a server.  The
   Value field of this TCP-Message contains a DER-encoded PKIMessage.

   The type of PKIMessages that can be carried by pkiReq TCP-Messages
   are (in the order they are defined in [RFC4210]):
      [0] Initialization Request
      [2] Certification Request
      [4] PKCS-10 Request
      [6] pop Response
      [7] Key Update Request





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      [9] Key Recovery Request
      [11] Revocation Request
      [13] Cross-Certification Request
      [15] CA Key Update Announcement
      [16] Certificate Announcement
      [17] Revocation Announcement
      [18] CRL Announcement
      [20] Nested Message
      [21] General Message
      [23] Error Message
      [24] Certificate Confirmation
      [25] Polling Request

4.4.2.  pkiRep

   TCP-Messages of this type are used to send a response to the
   requestor.  The Value field of the pkiRep contains a DER encoded
   PKIMessage.

   The type of PKIMessages that can be carried by such pkiRep messages
   are (in the order they are defined in [RFC4210]):
      [1] Initialization Response
      [3] Certification Response
      [5] pop Challenge
      [8] Key Update Response
      [10] Key Recovery Response
      [12] Revocation Response
      [14] Cross-Certificate Response
      [19] Confirmation
      [22] General Response
      [23] Error Message
      [26] Polling Response

4.4.3.  pollReq

   A pollReq is used by a client to check the status of a pending TCP-
   Message.  The Value portion of a pollReq contains:

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                       Polling-Reference                       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+








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   Polling-Reference: 32 bits (unsigned integer)
       This polling-reference MUST be the one returned via the
       respective pollRep TCP-Message.

4.4.4.  pollRep

   A pollRep is sent by the server to the client as response in case
   there is no PKIMessage ready yet.  The Value portion of the pollRep
   looks as follows:

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                       Polling-Reference                       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                       Time-to-Check-Back                      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Polling-Reference: 32 bits (unsigned integer)
       A unique 32-bit number identifying the transaction.

   Time-to-Check-Back: 32 bits (unsigned integer)
       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.

4.4.5.  finRep

   A finRep is sent by the server whenever no other response applies,
   such as after receiving a CMP pkiConf.  The Value portion of the
   finRep SHALL contain:

      0 1 2 3 4 5 6 7
     +-+-+-+-+-+-+-+-+
     |     '00'H     |
     +-+-+-+-+-+-+-+-+

   '00'H: 8 bits
       All bits set to zero.

4.4.6.  errorMsgRep

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





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   o  Invalid protocol version
   o  Invalid TCP message-type
   o  Invalid polling reference number

   The Value field of the errorMsgRep TCP-Message MUST contain:

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |          Error-Type           |         Data-Length           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     \                                                               \
     /                     Data  (variable length)                   /
     \                                                               \
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Error-Type: 16 bits  A value (format described below) indicating the
       type of the error.

   Data-Length: 16 bits (unsigned integer)  Contains the length of the
       Data field in number of octets.  Error messages not conveying
       additional information MUST set Data-Length to 0.

   Data: <data-length> octets
       An UTF8 text string for user readable error messages, containing
       additional information about the error.  Note that it does not
       contain a terminating NULL character at the end.  It SHOULD
       include an [RFC5646] language tag, as described in [RFC2482]

   The Error-Type is in the format 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:

     ID Value   Major Categories
     --------   ----------------
      '01'H      TCP-Message version negotiation
      '02'H      client errors
      '03'H      server errors

   The major categories '80'H-'FF'H are reserved for application use.

   The different error-types are discussed in the following sections:

4.4.6.1.  VersionNotSupported

   The VersionNotSupported errorMsgRep is defined as follows:





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               +------------------+------------------------+
               | Field            | Value                  |
               +------------------+------------------------+
               | Error-Type       | '0101'H                |
               |                  |                        |
               | Data-Length      | 1                      |
               |                  |                        |
               | Data             | <version>              |
               |                  |                        |
               | UTF8-text String | implementation defined |
               +------------------+------------------------+

   where <version> is the highest TCP-Message protocol version the
   server supports.

4.4.6.2.  GeneralClientError

   The GeneralClientError errorMsgRep is defined as follows:

               +------------------+------------------------+
               | Field            | Value                  |
               +------------------+------------------------+
               | Error-Type       | '0200'H                |
               |                  |                        |
               | Data-Length      | 0                      |
               |                  |                        |
               | Data             | <empty>                |
               |                  |                        |
               | UTF8-text String | implementation defined |
               +------------------+------------------------+

4.4.6.3.  InvalidMessageType

   The InvalidMessageType errorMsgRep is defined as follows:

               +------------------+------------------------+
               | Field            | Value                  |
               +------------------+------------------------+
               | Error-Type       | '0201'H                |
               |                  |                        |
               | Data-Length      | 1                      |
               |                  |                        |
               | Data             | <message-type>         |
               |                  |                        |
               | UTF8-text String | implementation defined |
               +------------------+------------------------+

   where <message-type> is the invalid Message-Type ID received by the



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   server.

4.4.6.4.  InvalidPollID

   The InvalidPollID errorMsgRep is defined as follows:

               +------------------+------------------------+
               | Field            | Value                  |
               +------------------+------------------------+
               | 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, identifying the transaction.

4.4.6.5.  GeneralServerError

   The GeneralServerError errorMsgRep is defined as follows:

               +------------------+------------------------+
               | Field            | Value                  |
               +------------------+------------------------+
               | Error-Type       | '0300'H                |
               |                  |                        |
               | Data-Length      | 0                      |
               |                  |                        |
               | Data             | <empty>                |
               |                  |                        |
               | UTF8-text String | implementation defined |
               +------------------+------------------------+















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5.  File-Based Protocol

   A file containing a PKIMessage MUST contain only the DER encoding of
   one PKIMessage, there MUST NOT be extraneous header or trailer
   information in the file.

   Such files can be used to transport PKIMessage sequences using e.g.
   FTP.











































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6.  Mail-Based Protocol

   This subsection specifies a means for conveying ASN.1-encoded
   messages for the protocol exchanges via Internet mail [RFC5321].  A
   simple MIME object is specified as follows.

         Content-Type: application/pkixcmp
         Content-Transfer-Encoding: base64

         <<the ASN.1 DER-encoded PKIX-CMP message, base64-encoded>>

   This MIME object can be sent and received using common MIME
   processing engines and provides a simple Internet mail transport for
   PKIX-CMP messages.  Implementations MAY wish to also recognize and
   use the "application/x-pkixcmp" MIME type (specified in earlier
   versions of this document) in order to support backward compatibility
   wherever applicable.


































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7.  Security Considerations

   Four aspects need to be considered by server side implementers:

   1.  There is the risk for denial of service attacks through resource
       consumption by opening many connections, therefore idle
       connections should be terminated after an appropriate timeout,
       maybe also depending on the available free resources.  After
       sending a CMP Error Message, the server should close the
       connection even if the CMP transaction is not yet fully
       completed.

   2.  There is no security at the TCP and HTTP protocol level (unless
       tunneled via SSL/TLS) and thus information from TCP-Messages or
       the HTTP protocol SHOULD NOT be used to change state of the
       transaction.  Change of state SHOULD be triggered by the signed
       PKIMessages which are carried within the TCP-Message.

   3.  If the server is going to be sending messages with sensitive
       information (not meant for public consumption) in the clear, it
       is RECOMMENDED that the server sends back the message directly
       and not use the TCP-Message pollRep.

   4.  The TCP-Message polling request/response mechanism can be used
       for all kinds of denial of service attacks.  It is RECOMMENDED
       that a server does not change the polling-reference between
       polling requests.
























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8.  Information Security Considerations

   CMP provides inbuilt integrity protection and authentication.  Due to
   the nature of a PKI, from a security perspective the information
   communicated unencrypted does not contain sensitive information.

   However, it might be possible for an interceptor to utilize the
   available information to gather confidential technical or business
   critical information.  Therefore, users of the HTTP CMP transport
   might want to use HTTP over TLS according to [RFC2818] or should
   consider to use virtual private networks created e.g. utilizing
   Internet Protocol Security according to [RFC4301].







































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9.  IANA Considerations

   The IANA has already registered TCP and UDP port 829 for "PKIX-3
   CA/RA" and the MIME media type "application/pkixcmp" for identifying
   CMP sequences.

   No further action by the IANA is necessary for this document or any
   anticipated updates.











































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10.  References

10.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2616]  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.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, January 2005.

   [RFC4210]  Adams, C., Farrell, S., Kause, T., and T. Mononen,
              "Internet X.509 Public Key Infrastructure Certificate
              Management Protocol (CMP)", RFC 4210, September 2005.

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, May 2008.

   [RFC5321]  Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,
              October 2008.

   [RFC5646]  Phillips, A. and M. Davis, "Tags for Identifying
              Languages", BCP 47, RFC 5646, September 2009.

10.2.  Informative References

   [RFC1945]  Berners-Lee, T., Fielding, R., and H. Nielsen, "Hypertext
              Transfer Protocol -- HTTP/1.0", RFC 1945, May 1996.

   [RFC2482]  Whistler, K. and G. Adams, "Language Tagging in Unicode
              Plain Text", RFC 2482, January 1999.

   [RFC2510]  Adams, C. and S. Farrell, "Internet X.509 Public Key
              Infrastructure Certificate Management Protocols",
              RFC 2510, March 1999.

   [RFC2818]  Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.

   [RFC4301]  Kent, S. and K. Seo, "Security Architecture for the
              Internet Protocol", RFC 4301, December 2005.





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Appendix A.  Acknowledgments

   Until the fifth draft version of this document, released in November
   24th 2000, the sole authors were Amit Kapoor and Ronald Tschlaer from
   Certicom.  Up to this point, besides editorial changes, the now
   deprecated TCP-Based transport was described as it is still included
   herein.  They are not available for this working on this document
   anymore at the time it is entering the "Authors Final Review state
   AUTH48".  As they therefore cannot approve this document as it would
   be necessary, their names were moved to this section.  Their contact
   data, as originally stated by them, is as follows:

      Amit Kapoor
      Certicom
      25801 Industrial Blvd
      Hayward, CA
      US
      Email: amit@trustpoint.com

      Ronald Tschalaer
      Certicom
      25801 Industrial Blvd
      Hayward, CA
      US
      Email: ronald@trustpoint.com

   The authors gratefully acknowledge the contributions of various
   members of the IETF PKIX Working Group and the ICSA CA-talk mailing
   list (a list solely devoted to discussing CMP interoperability
   efforts).

   By providing ideas, giving hints and doing invaluable review work,
   the following individuals, listed alphabetically, have significantly
   contributed to this document:

      Tomas Gustavsson, Primekey
      Peter Gutmann, University of Auckland
      Wolf-Dietrich Moeller, Nokia Siemens Networks













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Appendix B.  Registration of the application/pkixcmp Media Type


















































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   To: ietf-types@iana.org
   Subject: Registration of MIME media type application/pkixcmp

   MIME media type name: application

   MIME subtype name: pkixcmp

   Required parameters: -

   Optional parameters: -

   Encoding considerations:

   Content may contain arbitrary octet values (the ASN.1 DER encoding
   of a PKIMessage sequence, as defined in the IETF PKIX Working Group
   specifications).  base64 encoding is required for MIME e-mail; no
   encoding is necessary for HTTP.

   Security considerations:

   This MIME type may be used to transport Public-Key Infrastructure
   (PKI) messages between PKI entities.  These messages are defined by
   the IETF PKIX Working Group and are used to establish and maintain
   an Internet X.509 PKI.  There is no requirement for specific
   security mechanisms to be applied at this level if the PKI messages
   themselves are protected as defined in the PKIX specifications.

   Interoperability considerations: -

   Published specification: this document

   Applications which use this media type: Applications using
   certificate management, operational, or ancillary protocols (as
   defined by the IETF PKIX Working Group) to send PKI messages via
   E-Mail or HTTP.

   Additional information:

     Magic number (s): -
     File extension (s): ".PKI"
     Macintosh File Type Code (s): -

   Person and email address to contact for further information:
   Martin Peylo, martin.peylo@nsn.com

   Intended usage: COMMON

   Author/Change controller: Martin Peylo



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Authors' Addresses

   Tomi Kause
   SSH Communications Security Corp.
   Fredrikinkatu 42
   Helsinki  00100
   Finland

   Email: toka@ssh.com


   Martin Peylo
   Nokia Siemens Networks
   Linnoitustie 6
   Espoo  02600
   Finland

   Email: martin.peylo@nsn.com

































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