PKIX Working Group J. Schaad
Internet Draft Soaring Hawk Consulting
Document: draft-ietf-pkix-cmc-trans-02.txt M.Myers
February 2005 TraceRoute Security
Expires: July 2005 X.Liu
Cisco
J. Weinstein
CMC Transport
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Copyright Notice
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Abstract
This document defines a number of transport mechanisms that are used
to move [CMC] messages. The transport mechanisms described in this
document are: HTTP, file, mail and TCP.
1. Overview
This document defines a number of transport methods that are used to
move [CMC] messages. The transport mechanisms described in this
document are: HTTP, file, mail and TCP.
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 [RFC 2119].
2. File based protocol
Enrollment messages and responses may be transferred between clients
and servers using file system-based mechanisms, such as when
enrollment is performed for an off-line client. When files are used
to transport binary, BER-encoded Full Enrollment Request and
Response messages, there MUST be only one instance of a request or
response message in a single file. The following file type
extensions SHOULD be used:
Message Type File Extension
Full PKI Request .crq
Full PKI Response .crp
3. Mail based protocol
MIME wrapping is defined for those environments that are MIME
native.
The basic mime wrapping in this section is taken from [SMIMEV2] and
[SMIMEV3]. Simple enrollment requests are encoded using the
"application/pkcs10" content type. A file name MUST be included
either in a content type or a content disposition statement. The
extension for the file MUST be ".p10".
Simple enrollment response messages MUST be encoded as content-type
"application/pkcs7-mime". An smime-type parameter MUST be on the
content-type statement with a value of "certs-only." A file name
with the ".p7c" extension MUST be specified as part of the content-
type or content-disposition statement.
Full enrollment request messages MUST be encoded as content-type
"application/pkcs7-mime". The smime-type parameter MUST be included
with a value of "CMC-enroll". A file name with the ".p7m" extension
MUST be specified as part of the content-type or content-disposition
statement.
Full enrollment response messages MUST be encoded as content-type
"application/pkcs7-mime". The smime-type parameter MUST be included
with a value of "CMC-response." A file name with the ".p7m"
extensions MUST be specified as part of the content-type or content-
disposition statement.
MIME TYPE File Extension SMIME-TYPE
application/pkcs10 .p10 N/A
(simple PKI request)
application/pkcs7-mime .p7m CMC-request
(full PKI request)
application/pkcs7-mime .p7c certs-only
(simple PKI response)
application/pkcs7-mime .p7m CMC-response
(full PKI response)
4. HTTP/HTTPS based protocol
HTTP messages are wrapped with by a mime object as specified above.
5. TCP based protocol
When CMC messages are sent over a TCP-Based connection, no wrapping
is required of the message. Messages are sent in their binary
encoded form.
The connection is closed by the server after generating a response
for the client. (All CMC request messages from client to server
generate a response message.) If a second set of messages from the
client to the server is required to complete the transaction, the
client generates a new TCP-Based connection for this purpose; it
cannot reuse an existing one.
Out of band setup can be used to keep a TCP-Based connection open
for more than one message pair. A situation where this can occur is
an RA talking to a CA over a specially setup TCP connection.
6 Socket-Based Transport
When enrollment messages and responses are sent over sockets, no
wrapping is required. Messages MUST be sent in their binary, BER-
encoded form.
7. Security Considerations
Mechanisms for thwarting replay attacks may be required in
particular implementations of this protocol depending on the
operational environment. In cases where the CA maintains significant
state information, replay attacks may be detectable without the
inclusion of the optional nonce mechanisms. Implementers of this
protocol need to carefully consider environmental conditions before
choosing whether or not to implement the senderNonce and
recipientNonce attributes described in section 5.6. Developers of
state-constrained PKI clients are strongly encouraged to incorporate
the use of these attributes.
8. Acknowledgments
The authors would like to thank Brian LaMacchia for his work in
developing and writing up many of the concepts presented in this
document. The authors would also like to thank Alex Deacon and Barb
Fox for their contributions.
9. References
[CMC] J. Schaad, M. Myers, X. Liu, J. Weinstein, "Certificate
Management Messages over CMS",
draft-ietf-pkix-cmc-base-03.txt.
[RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[SMIMEV2] Dusse, S., Hoffman, P., Ramsdell, B., Lundblade, L. and
L.
Repka, "S/MIME Version 2 Message Specification", RFC
2311,
March 1998.
[SMIMEV3] Ramsdell, B., "S/MIME Version 3 Message Specification",
RFC 2633, June 1999.
10. Authors' Addresses
Jim Schaad
Soaring Hawk Consulting
EMail: jimsch@exmsft.com
Michael Myers
TraceRoute Security, Inc.
EMail: myers@coastside.net
Xiaoyi Liu
Cisco Systems
170 West Tasman Drive
San Jose, CA 95134
Phone: (480) 526-7430
EMail: xliu@cisco.com
Jeff Weinstein
EMail: jsw@meer.net
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