One document matched: draft-ietf-pkix-cmp-tcp-00.txt
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
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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].
1. 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.
2. 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.
3. 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.
4. Security Considerations
No new security considerations with respect to [CMP] are introduced.
5. 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;
6. 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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