Internet DRAFT - draft-ietf-pkix-cmp-transport-protocols
draft-ietf-pkix-cmp-transport-protocols
Network Working Group T. Kause
Internet-Draft Tectia
Updates: 4210 (if approved) M. Peylo
Intended status: Standards Track NSN
Expires: January 25, 2013 July 24, 2012
Internet X.509 Public Key Infrastructure -- HTTP Transfer for CMP
draft-ietf-pkix-cmp-transport-protocols-20.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
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 January 25, 2013.
Copyright Notice
Copyright (c) 2012 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.
Kause & Peylo Expires January 25, 2013 [Page 1]
Internet-Draft CMPtrans July 2012
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 . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions Used in This Document . . . . . . . . . . . . . . 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. Pushing of Announcements . . . . . . . . . . . . . . . . . 7
3.8. HTTP Considerations . . . . . . . . . . . . . . . . . . . 8
4. Implementation Considerations . . . . . . . . . . . . . . . . 10
5. Security Considerations . . . . . . . . . . . . . . . . . . . 11
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 13
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
8.1. Normative References . . . . . . . . . . . . . . . . . . . 14
8.2. Informative References . . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15
Kause & Peylo Expires January 25, 2013 [Page 2]
Internet-Draft CMPtrans July 2012
1. Introduction
The Certificate Management Protocol (CMP) [RFC4210] requires a well
defined transfer mechanism to enable End Entities (EEs), Registration
Authorities (RAs) and Certification Authorities (CAs) to pass
PKIMessage sequences between them.
The first version of the CMP specification [RFC2510] included a brief
description of a simple transfer protocol layer on top of TCP. Its
features was simple transfer 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 transfer, but those were not specified in detail.
The current version of the CMP specification [RFC4210] incorporated
its own polling mechanism and thus the need for a transfer protocol
providing this functionality vanished. The remaining features CMP
requires from its transfer protocols are connection and error
handling.
Before this document was published as an RFC, the draft version
underwent drastic changes during the long-lasting work process. The
so-called "Direct TCP-Based Management Protocol" specified in
[RFC2510] was enhanced and at some point a version existed where this
protocol was again transferred over HTTP. As both approaches proved
to be needless and cumbersome, implementers preferred to use plain
HTTP transfer following [RFC1945] or [RFC2616]. This document now
reflects that by exclusively describing HTTP as transfer protocol for
CMP.
The usage of HTTP for transferring CMP messages exclusively uses POST
method for requests, effectively tunneling CMP over HTTP. While this
is generally considered as bad practice and should not be emulated,
there are good reasons to do so for transferring CMP. HTTP is used
as it is generally easy to implement and able to traverse network
borders utilizing ubiquitous proxies. Most importantly, HTTP is
already commonly used in existing CMP implementations. Other HTTP
request methods such as GET are not used as PKI management operations
can only be triggered using CMP's PKI messages which need to be
transferred using a POST request.
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
Kause & Peylo Expires January 25, 2013 [Page 3]
Internet-Draft CMPtrans July 2012
of HTTP is not blocking its usage as transfer protocol for CMP
messages.
Kause & Peylo Expires January 25, 2013 [Page 4]
Internet-Draft CMPtrans July 2012
2. Conventions Used in This Document
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].
Kause & Peylo Expires January 25, 2013 [Page 5]
Internet-Draft CMPtrans July 2012
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.
3.1. HTTP Versions
Implementations MUST support HTTP/1.0 [RFC1945], and SHOULD support
HTTP/1.1 [RFC2616].
3.2. Persistent Connections
HTTP persistent connections [RFC2616] allow multiple interactions to
take place on the same HTTP connection. However, neither HTTP nor
the protocol specified in this document are designed to correlate
messages on the same connection in any meaningful way; persistent
connections are only a performance optimization. In particular,
intermediaries can do things like mix connections from different
clients into one "upstream" connections, terminate persistent
connections and forward requests as non-persistent requests, etc. As
such, implementations MUST NOT infer that requests on the same
connection come from the same client (e.g., for correlating PKI
messages with ongoing transactions); every message is to be evaluated
in isolation.
3.3. General Form
A DER-encoded [ITU.X690.1994] PKIMessage [RFC4210] is sent as the
entity-body of an HTTP POST request. If this HTTP request is
successful, the server returns the CMP response in the body of the
HTTP response. The HTTP response status code in this case MUST be
200; other "Successful 2xx" codes MUST NOT be used for this purpose.
HTTP responses to pushed CMP Announcement messages (i.e., CA
Certificate Announcement, Certificate Announcement, Revocation
Announcement, and CRL Announcement) utilize the status codes 201 and
202 to identify whether the received information was processed.
While "Redirection 3xx" status codes MAY be supported by
implementations, clients should only be enabled to automatically
follow them after careful consideration of possible security
implications. As described in Section 5, "301 Moved Permanently"
could be misused for permanent denial of service.
All applicable "Client Error 4xx" or "Server Error 5xx" status codes
MAY be used to inform the client about errors.
Kause & Peylo Expires January 25, 2013 [Page 6]
Internet-Draft CMPtrans July 2012
3.4. Media Type
The Internet Media Type "application/pkixcmp" MUST be set in the HTTP
Content-Type header field 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 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 transferred CMP message
was not successfully delivered to its destination.
3.6. HTTP Request-URI
The Request-URI is formed as specified in [RFC3986].
A server implementation MUST handle Request-URI paths with or without
a trailing slash as identical.
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" path
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
3.7. Pushing of Announcements
A CMP server may create event-triggered announcements or generate
them on a regular basis. It MAY utilize HTTP transfer to convey them
to a suitable recipient. As no request messages are specified for
those announcements 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
Kause & Peylo Expires January 25, 2013 [Page 7]
Internet-Draft CMPtrans July 2012
described in E.5 of [RFC4210] can be used.
When pushing Announcement messages, PKIMessage 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" status code and empty message body.
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 sender may then try
to send the Announcement again and may repeat this until it receives
a confirmation that it had been successfully processed. 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
While all defined features of the HTTP protocol are available to
implementations, they SHOULD keep the protocol utilization as simple
as possible. E.g. there is no benefit in using chunked Transfer-
Encoding as the length of an ASN.1 sequence is know when starting to
send it.
Kause & Peylo Expires January 25, 2013 [Page 8]
Internet-Draft CMPtrans July 2012
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
seldom reject a message without evaluating the body.
Kause & Peylo Expires January 25, 2013 [Page 9]
Internet-Draft CMPtrans July 2012
4. Implementation Considerations
Implementors should be aware that implementations might exist that
use a different approach for transferring CMP over HTTP because this
document has been under development for more than a decade. Further,
implementations based on earlier drafts of this document might use an
unregistered "application/pkixcmp-poll" MIME type.
Kause & Peylo Expires January 25, 2013 [Page 10]
Internet-Draft CMPtrans July 2012
5. Security Considerations
The following aspects need to be considered by implementers and
users:
1. There is the risk for denial of service attacks through resource
consumption by opening many connections to an HTTP server.
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. Without being encapsulated in effective security protocols such
as TLS [RFC5246] there is no integrity protection at the HTTP
protocol level. Therefore information from the HTTP protocol
should not be used to change state of the transaction.
3. Client users should be aware that storing the target location of
a HTTP response with the "301 Moved Permanently" status code
could be exploited by a man-in-the-middle attacker to block them
permanently from contacting the correct server.
4. If no measures to authenticate and protect the HTTP responses to
pushed Announcement messages are in place their information
regarding the Announcement's processing state may not be trusted.
In that case the overall design of the PKI system must not depend
on the Announcements being reliably received and processed by
their destination.
5. CMP provides inbuilt integrity protection and authentication.
The information communicated unencrypted in CMP messages does not
contain sensitive information endangering the security of the PKI
when intercepted. However, it might be possible for an
eavesdropper to utilize the available information to gather
confidential technical or business critical information.
Therefore users of the HTTP transfer for CMP might want to
consider using HTTP over TLS according to [RFC2818] or virtual
private networks created e.g. by utilizing Internet Protocol
Security according to [RFC4301]. Compliant implementations MUST
support TLS with the option to authenticate both server and
client.
Kause & Peylo Expires January 25, 2013 [Page 11]
Internet-Draft CMPtrans July 2012
6. IANA Considerations
The IANA has already registered the MIME media type "application/
pkixcmp" for identifying CMP sequences due to an request made in
connection with [RFC2510].
No further action by the IANA is necessary for this document or any
anticipated updates.
Kause & Peylo Expires January 25, 2013 [Page 12]
Internet-Draft CMPtrans July 2012
7. Acknowledgments
Amit Kapoor and Ronald Tschlaer were the original authors of this
document and their version focused on the so-called "TCP-Based
Management Protocol", which has been removed from this document.
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 alphabetically listed individuals have significantly
contributed to this document:
Tomas Gustavsson, Primekey
Peter Gutmann, University of Auckland
Wolf-Dietrich Moeller, Nokia Siemens Networks
Kause & Peylo Expires January 25, 2013 [Page 13]
Internet-Draft CMPtrans July 2012
8. References
8.1. Normative References
[ITU.X690.1994]
International Telecommunications Union, "Information
Technology - ASN.1 encoding rules: Specification of Basic
Encoding Rules (BER), Canonical Encoding Rules (CER) and
Distinguished Encoding Rules (DER)", ITU-T Recommendation
X.690, 1994.
[RFC1945] Berners-Lee, T., Fielding, R., and H. Nielsen, "Hypertext
Transfer Protocol -- HTTP/1.0", RFC 1945, May 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2510] Adams, C. and S. Farrell, "Internet X.509 Public Key
Infrastructure Certificate Management Protocols",
RFC 2510, March 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.
[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.
8.2. Informative References
[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.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
Kause & Peylo Expires January 25, 2013 [Page 14]
Internet-Draft CMPtrans July 2012
Authors' Addresses
Tomi Kause
Tectia Corporation
Kumpulantie 3
Helsinki 00520
Finland
Email: toka@tectia.com
Martin Peylo
Nokia Siemens Networks
Linnoitustie 6
Espoo 02600
Finland
Email: martin.peylo@nsn.com
Kause & Peylo Expires January 25, 2013 [Page 15]
