Network Working Group T. Kause
Internet-Draft Tectia
Updates: 4210 (if approved) M. Peylo
Intended status: Standards Track NSN
Expires: January 1, 2012 June 30, 2011
Internet X.509 Public Key Infrastructure -- HTTP Transport for CMP
draft-ietf-pkix-cmp-transport-protocols-13.txt
Abstract
This document describes how to layer the Certificate Management
Protocol over HTTP. It is the "CMPtrans" document referenced in RFC
4210 and therefore updates the reference given therein.
Status of this Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. HTTP-Based Protocol . . . . . . . . . . . . . . . . . . . . . 5
3.1. HTTP Versions . . . . . . . . . . . . . . . . . . . . . . 5
3.2. Persistent Connections . . . . . . . . . . . . . . . . . . 5
3.3. General Form . . . . . . . . . . . . . . . . . . . . . . . 5
3.4. Media Type . . . . . . . . . . . . . . . . . . . . . . . . 5
3.5. Communication Workflow . . . . . . . . . . . . . . . . . . 6
3.6. HTTP Request-URI . . . . . . . . . . . . . . . . . . . . . 6
3.7. Pushing of Announcements . . . . . . . . . . . . . . . . . 7
3.8. HTTP Considerations . . . . . . . . . . . . . . . . . . . 8
4. Compatibility Issues with Legacy Implementations . . . . . . . 9
5. Security Considerations . . . . . . . . . . . . . . . . . . . 10
6. Information Security Considerations . . . . . . . . . . . . . 11
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
8.1. Normative References . . . . . . . . . . . . . . . . . . . 13
8.2. Informative References . . . . . . . . . . . . . . . . . . 13
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 14
Appendix B. Registration of the application/pkixcmp Media Type . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17
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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 transport protocol layer on top of TCP. Its
features was 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, but those were not specified in detail.
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 protocol was enhanced and a
TCP-Messages-over-HTTP transport specification appeared. As both
proved to be needless and cumbersome, implementers preferred to use
plain HTTP transport. This document now reflects that by exclusively
describing HTTP as transport protocol for CMP.
HTTP transport is generally easy to implement, traverses network
borders utilizing ubiquitous proxies and is already commonly found in
existing implementations.
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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 spanning
over 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. Both server and client SHOULD be able to interact with
counterparts utilizing either 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.
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. HTTP responses with empty message body to pushed CMP
Announcement messages utilize the status codes 201, 202 and 204 to
identify whether the received information was processed.
All applicable 4xx or 5xx status codes may be used to inform the
client about errors.
3.4. Media Type
The Internet Media Type "application/pkixcmp" MUST be set in the HTTP
header when conveying a PKIMessage.
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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 certain events or done
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.
If the receipt of an HTTP request is not confirmed by receiving an
HTTP response, it MUST be assumed that the transported CMP message
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 the 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
[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
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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 domain.
3.7. Pushing of 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. No request message for is
specified, so they can only be pushed to the recipient. If an EE
wants to poll for a potential CA Key Update Announcement or the
current CRL, a PKI Information Request using a General Message as
described in E.5 of [RFC4210] can be used.
When pushing Annocements, 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,
the recipient MUST acknowledge receipt with a HTTP response having an
appropriate status code and an empty body. When not receiving such
response it MUST be assumed that the delivery was not successful and
if applicable the sending side may retry sending the Announcement
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 response with a "201
Created" or "204 No Content" status code and empty message body.
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In case the announced information was only accepted for further
processing, the status code of the returned HTTP response MAY also 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.
3.8. HTTP Considerations
In general CMP messages are not cachable. HTTP headers of requests
and responses MUST include "Cache-Control: no-cache" and, in case of
HTTP/1.0, additionally "Pragma: no-cache" to protect 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 a message without evaluating the body.
Content codings MAY be applied.
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4. 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 the
DER-encoded PKIMessage prefixed by an additional "TCP-Messaging"
protocol. TCP-Messaging was described in draft versions of this
document but was removed.
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5. Security Considerations
The following 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 HTTP protocol level (unless tunneled
via TLS) and thus information from the HTTP protocol SHOULD NOT
be used to change state of the transaction. Change of state
SHOULD be triggered by signed PKIMessages only. Likewise, the
clients SHOULD NOT support the 301 HTTP status code which could
otherwise be used by an man-in-the-middle attacker to barr them
permanently from contacting the correct server.
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6. 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. by utilizing
Internet Protocol Security according to [RFC4301].
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7. 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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8. References
8.1. 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.
8.2. 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 the now removed TCP-Based transport was
described in detail. 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
Tectia Corporation
Fredrikinkatu 42
Helsinki 00100
Finland
Email: toka@tectia.com
Martin Peylo
Nokia Siemens Networks
Linnoitustie 6
Espoo 02600
Finland
Email: martin.peylo@nsn.com
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