Network Working Group A. Kapoor
Internet-Draft R. Tschalar
Updates: 2510 (if approved) Certicom
Expires: August 9, 2004 T. Kause
SSH
February 9, 2004
Internet X.509 Public Key Infrastructure -- Transport Protocols for
CMP
draft-ietf-pkix-cmp-transport-protocols-05.txt
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
This document describes how to layer Certificate Management Protocols
over various transport protocols.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements . . . . . . . . . . . . . . . . . . . . . . . 4
3. TCP-Based Management Protocol . . . . . . . . . . . . . . 5
3.1 General Form . . . . . . . . . . . . . . . . . . . . . . . 5
3.2 Version Negotiation . . . . . . . . . . . . . . . . . . . 6
3.3 TCP-message Version 10 . . . . . . . . . . . . . . . . . . 6
3.4 Detecting and Interoperating with RFC-2510 Conformant
Implementations . . . . . . . . . . . . . . . . . . . . . 7
3.5 Message Types . . . . . . . . . . . . . . . . . . . . . . 7
3.5.1 pkiReq . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.5.2 pkiRep . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.5.3 pollReq . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.5.4 pollRep . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.5.5 finRep . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.5.6 errorMsgRep . . . . . . . . . . . . . . . . . . . . . . . 10
3.5.7 VersionNotSupported errorMsgRep . . . . . . . . . . . . . 11
3.5.8 GeneralClientError errorMsgRep . . . . . . . . . . . . . . 11
3.5.9 InvalidMessageType errorMsgRep . . . . . . . . . . . . . . 12
3.5.10 InvalidPollID errorMsgRep . . . . . . . . . . . . . . . . 12
3.5.11 GeneralServerError errorMsgRep . . . . . . . . . . . . . . 12
4. HTTP-Based Management Protocol . . . . . . . . . . . . . . 13
5. File based protocol . . . . . . . . . . . . . . . . . . . 14
6. Mail based protocol . . . . . . . . . . . . . . . . . . . 15
7. Security Considerations . . . . . . . . . . . . . . . . . 16
Normative References . . . . . . . . . . . . . . . . . . . 17
Informative References . . . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . 18
A. Acknowledgments . . . . . . . . . . . . . . . . . . . . . 19
B. Registration of MIME Type for E-Mail or HTTP Use . . . . . 20
Intellectual Property and Copyright Statements . . . . . . 22
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1. Introduction
Well defined transport mechanisms are required for Certificate
Management Protocol [CMP] in order to allow end entities, RAs and CAs
to pass PKI messages between them.
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2. Requirements
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].
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3. TCP-Based Management Protocol
While this section is called TCP-Based and the messages are called
TCP-message's, 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. Note that 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 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.
3.1 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
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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).
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.
3.2 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.
3.3 TCP-message Version 10
The TCP-message version will be 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.
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 receivers, 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
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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
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.
3.4 Detecting and Interoperating with RFC-2510 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.
Clients wishing to interoperate with [RFC2510] compliant servers
SHOULD treat a response with a version less than 10 as an [RFC2510]
style message. If this message is an errorMsgRep (message-type 06)
then the client MAY automatically retry the request using the
[RFC2510] format; if the message is not an errorMsgRep or the
implementation does not wish to support [RFC2510] then it MUST abort
the corresponding CMP transaction.
3.5 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
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finRep '03'H
pkiRep '05'H
errorMsgRep '06'H
If server receives an unknown message-type then it MUST reply with an
InvalidMessageType errorMsgRep. If a client receives an unknown
message-type then it MUST abort the CMP transaction.
The different TCP-messages are discussed in the following sections:
3.5.1 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:
CRL Announcement
Certificate Confirmation
Poll Request
Subscription Request
CA Key Update Announcement
Certificate Announcement
Certification Request
Cross-Certification Request
Error Message
General Message
Initialization Request
Key Recovery Request
Key Update Request
Nested Message
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PKCS-10 Request
POP Response
Revocation Request
3.5.2 pkiRep
This TCP-message is to be used to send back the response to the
request. The <value> portion of the pkiRep will contain: DER encoded
PKI message
The type of PKIMessages that can be carried by this TCP-message are:
Confirmation
Poll Response
Subscription Response
Certification Response
Error Message
General Response
Initialization Response
Key Recovery Response
Key Update Response
POP Challenge
Revocation Response
3.5.3 pollReq
The pollReq will be the used by the client to check the status of a
pending TCP-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.
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3.5.4 pollRep
The pollRep will be the response sent by the server to the client
when there are no TCP-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.
3.5.5 finRep
finRep is sent by the server whenever no other response applies (such
as after receiving a CMP pkiConf), and usually indicates the end of
the CMP transaction. The <value> portion of the finRep SHALL contain:
'00'H (8 bits)
3.5.6 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 %lt;value> field of the TCP-message SHALL contain:
error-type (16-bits)
data-length (16-bits)
data (<data-length> octets)
UTF8 String (SHOULD include an [RFC3066] language tag, as
described in [RFC2482])
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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 major categories '80'H-'FF'H are reserved for application use.
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 MUST set the <data-length> to 0.
The UTF8 text string is for user readable error messages. Note that
it does not contain a terminating null character at the end.
3.5.7 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.
3.5.8 GeneralClientError errorMsgRep
The GeneralClientError errorMsgRep is defined as follows:
error-type: '0200'H
data-length: 0
data: <empty>
UTF8-text String: implementation defined
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3.5.9 InvalidMessageType errorMsgRep
The InvalidMessageType 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.
3.5.10 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.
3.5.11 GeneralServerError errorMsgRep
The GeneralServerError errorMsgRep is defined as follows:
error-type: '0300'H
data-length: 0
data: <empty>
UTF8-text String: implementation defined
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4. HTTP-Based Management Protocol
A client creates a TCP-message, as specified in section 2.0 XXX . The
message is then sent as the entity-body of an HTTP POST request as
specified in [RFC2616]. If the HTTP request is successful then the
server returns a similar message in the body of the response. The
response status code in this case MUST be 200; other 2xx codes MUST
NOT be used. The content type of the request and response MUST be
"application/pkixcmp". Applications MAY wish to also recognized and
use the "application/pkixcmp-poll" MIME type (specified in earlier
versions of this document) in order to support backward compatibility
wherever applicable. Content codings may be applied.
Note that a server may return any 1xx, 3xx, 4xx, or 5xx code if the
HTTP request needs further handling or is otherwise not acceptable.
Because in general CMP messages are not cacheable, requests and
responses should 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. This is especially important for polling
requests and responses.
Connection management SHOULD be based on the HTTP provided mechanisms
(Connection and Proxy-Connection header fields) and not on the
connection flag carried in the TCP-message.
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5. File based protocol
A file containing a PKI message MUST contain only the DER encoding of
one PKI message, i.e., there MUST be no extraneous header or trailer
information in the file.
Such files can be used to transport PKI messages 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 ([RFC821]. 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
Three aspects need to be considered by server side implementors:
1. There is no security at the TCP and HTTP protocol level (unless
tunneled via SSL/TLS) and thus TCP-message should not be used to
change state of the transaction. Change of state should be done
on the signed PKIMessage being carried within the TCP-message.
2. 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 send back the message directly and
not use the pollRep.
3. The polling request/response mechanism can be used for all kinds
of denial of service attacks. It is RECOMMENDED that the server
not change the polling-reference between polling requests.
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Normative References
[CMP] Adams, C., Farrell, S., Kause, T. and T. Mononen,
"Internet X.509 Public Key Infrastructure -- Certificate
Management Protocol (CMP)", RFC 2510bis, January 0000.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2482] Whistler, K. and G. Adams, "Language Tagging in Unicode
Plain Text", RFC 2482, January 1999.
[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.
[RFC3066] Alvestrand, H., "Tags for the Identification of
Languages", BCP 47, RFC 3066, January 2001.
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Informative References
[RFC821] Postel, J., "Simple Mail Transfer Protocol", STD 10, RFC
821, August 1982.
Authors' Addresses
Amit Kapoor
Certicom
25801 Industrial Blvd
Hayward, CA
US
EMail: amit@trustpoint.com
Ronald Tschalar
Certicom
25801 Industrial Blvd
Hayward, CA
US
EMail: ronald@trustpoint.com
Tomi Kause
SSH Communications Security Corp.
Fredrikinkatu 42
Helsinki 00100
Finland
EMail: toka@ssh.com
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Appendix A. Acknowledgments
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).
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Appendix B. Registration of MIME Type for E-Mail or HTTP Use
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 PKI message, 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:
Tomi Kause, toka@ssh.com
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Intended usage: COMMON
Author/Change controller: Tomi Kause
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