Internet DRAFT - draft-ietf-lamps-rfc6712bis
draft-ietf-lamps-rfc6712bis
LAMPS Working Group H. Brockhaus
Internet-Draft D. von Oheimb
Obsoletes: 6712 9480 (if approved) Siemens
Intended status: Standards Track M. Ounsworth
Expires: 2 September 2024 J. Gray
Entrust
1 March 2024
Internet X.509 Public Key Infrastructure -- HTTP Transfer for the
Certificate Management Protocol (CMP)
draft-ietf-lamps-rfc6712bis-04
Abstract
This document describes how to layer the Certificate Management
Protocol (CMP) over HTTP.
It includes the updates on RFC 6712 specified in CMP Updates RFC 9480
Section 3 and obsoleted both documents. These updates introduce CMP
URIs using a Well-known prefix.
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 https://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 2 September 2024.
Copyright Notice
Copyright (c) 2024 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 (https://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
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and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Changes Since RFC 6712 . . . . . . . . . . . . . . . . . 4
1.2. Changes Made by This Document . . . . . . . . . . . . . . 4
2. Conventions Used in This Document . . . . . . . . . . . . . . 4
3. HTTP-Based Protocol . . . . . . . . . . . . . . . . . . . . . 4
3.1. HTTP Versions . . . . . . . . . . . . . . . . . . . . . . 4
3.2. Persistent Connections . . . . . . . . . . . . . . . . . 5
3.3. General Form . . . . . . . . . . . . . . . . . . . . . . 5
3.4. Header Fields . . . . . . . . . . . . . . . . . . . . . . 5
3.5. Communication Workflow . . . . . . . . . . . . . . . . . 6
3.6. HTTP Request-URI . . . . . . . . . . . . . . . . . . . . 6
3.7. Pushing of Announcements . . . . . . . . . . . . . . . . 7
3.8. HTTP Considerations . . . . . . . . . . . . . . . . . . . 8
4. Implementation Considerations . . . . . . . . . . . . . . . . 8
5. Security Considerations . . . . . . . . . . . . . . . . . . . 8
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
8.1. Normative References . . . . . . . . . . . . . . . . . . 9
8.2. Informative References . . . . . . . . . . . . . . . . . 10
Appendix A. History of Changes . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction
[RFC Editor: please delete:
During IESG telechat the CMP Updates document was approved on
condition that LAMPS provides a RFC6712bis document. Version -00 of
this document shall be identical to RFC 6712 and version -01
incorporates the changes specified in CMP Updates Section 3.
A history of changes is available in Appendix A of this document.
The authors of this document wish to thank Tomi Kause and Martin
Peylo, the original authors of RFC 6712, for their work and invite
them, next to further volunteers, to join the -bis activity as co-
authors.
]
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[RFC Editor:
Please perform the following substitution.
* RFCXXXX ---> the assigned numerical RFC value for this draft
* RFCCCCC ---> the assigned numerical RFC value for
[I-D.ietf-lamps-rfc4210bis]
]
The Certificate Management Protocol (CMP) [RFCCCCC] 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 were 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 second 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.
CMP can benefit from utilizing a reliable transport and it requires
connection and error handling from the transfer protocol, which is
all covered by HTTP. Additionally, delayed delivery of CMP response
messages may be handled at transfer level, regardless of the message
contents. Since [RFC9480] extends the polling mechanism specified in
the second version of CMP [RFC4210] to cover all types of PKI
management transactions, delays detected at application level may
also be handled within CMP, using pollReq and pollRep messages.
The usage of HTTP for transferring CMP messages exclusively uses the
POST method for requests, effectively tunneling CMP over HTTP. While
this is generally considered 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 it is 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 because PKI management
operations can only be triggered using CMP's PKI messages, which need
to be transferred using a POST request.
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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 the transfer protocol for CMP
messages.
1.1. Changes Since RFC 6712
CMP Updates [RFC9480] updated [RFC6712], supporting the PKI
management operations specified in the Lightweight CMP Profile
[RFC9483], in the following areas:
* Introduce the HTTP URI path prefix '/.well-known/cmp'.
* Add options for extending the URI structure with further segments
and to this end define a new protocol registry group.
1.2. Changes Made by This Document
This document obsoletes RFC 6712 [RFC6712]. It includes the changes
specified by CMP Updates [RFC9480] Section 3 as described in
Section 1.1.
2. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
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 [RFC9112].
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3.2. Persistent Connections
HTTP persistent connections [RFC9112] 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" connection, 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 [RFCCCCC] 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 Certificate Revocation List (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.
3.4. Header Fields
The Internet Media Type "application/pkixcmp" MUST be set in the HTTP
Content-Type header field when conveying a PKIMessage.
The Content-Length header field SHOULD be provided, giving the length
of the ASN.1-encoded PKIMessages.
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3.5. Communication Workflow
In CMP, most communication is initiated by the EEs 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
Each CMP server on a PKI management entity supporting HTTP or HTTPS
transfer MUST support the use of the path prefix '/.well-known/' as
defined in [RFC8615] and the registered name 'cmp' to ease
interworking in a multi-vendor environment.
The CMP client needs to be configured with sufficient information to
form the CMP server URI. This is at least the authority portion of
the URI, e.g., 'www.example.com:80', or the full operation path
segment of the PKI management entity. Additionally, OPTIONAL path
segments MAY be added after the registered application name as part
of the full operation path to provide further distinction. The path
segment 'p' followed by an arbitraryLabel <name> could, for example,
support the differentiation of specific CAs or certificate profiles.
Further path segments, e.g., as specified in the Lightweight CMP
Profile [RFC9483], could indicate PKI management operations using an
operationLabel <operation>. A valid, full CMP URI can look like
this:
http://www.example.com/.well-known/cmp
http://www.example.com/.well-known/cmp/<operation>
http://www.example.com/.well-known/cmp/p/<name>
http://www.example.com/.well-known/cmp/p/<name>/<operation>
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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. In this use case, the CMP server acts as an
HTTP client, and the recipient needs to utilize an HTTP server. 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
described in Appendix E.5 of [RFCCCCC] 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, for example, be
repositories storing the announced information, such as directory
services. Those services 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 an HTTP response having
an appropriate status code and an empty body. When not receiving
such a response, it MUST be assumed that the delivery was not
successful. If applicable, the sending side MAY try sending the
Announcement again 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 an 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 has been successfully processed. The
appropriate duration of the delay and the option to increase it
between consecutive attempts should be carefully considered.
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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. For example, there is no benefit in using chunked
Transfer-Encoding, as the length of an ASN.1 sequence is known when
starting to send it.
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 Section 8.2.3 of [RFC9112]. The CMP
payload sent by a client is relatively small, so having extra
messages exchanged is inefficient, as the server will only seldom
reject a message without evaluating the body.
4. Implementation Considerations
Implementors should be aware that implementations might exist that
use a different approach for transferring CMP over HTTP, because
RFC 6712 [RFC6712] has been under development for more than a decade.
Further, implementations based on earlier drafts of RFC 6712
[RFC6712] might use an unregistered "application/pkixcmp-poll" MIME
type.
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; this may also depend 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 Transport Layer Security (TLS) [RFC5246] or [RFC8446], 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.
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3. Client users should be aware that storing the target location of
an HTTP response with the "301 Moved Permanently" status code
could be exploited by a man-in-the-middle attacker trying 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 [RFC9110] or virtual
private networks created, for example, by utilizing Internet
Protocol Security according to [RFC4301]. Compliant
implementations MUST support TLS with the option to authenticate
both server and client.
6. IANA Considerations
No further action by the IANA is necessary for this document or any
anticipated updates.
7. Acknowledgments
The authors of this document wish to thank Tomi Kause and Martin
Peylo, the original authors of [RFC6712], for their work.
We also thank all reviewers of this document for their valuable
feedback.
8. References
8.1. Normative References
[RFC1945] Berners-Lee, T., Fielding, R., and H. Frystyk, "Hypertext
Transfer Protocol -- HTTP/1.0", RFC 1945,
DOI 10.17487/RFC1945, May 1996,
<https://www.rfc-editor.org/rfc/rfc1945>.
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[RFC8615] Nottingham, M., "Well-Known Uniform Resource Identifiers
(URIs)", RFC 8615, DOI 10.17487/RFC8615, May 2019,
<https://www.rfc-editor.org/rfc/rfc8615>.
[RFC9112] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "HTTP/1.1", STD 99, RFC 9112, DOI 10.17487/RFC9112,
June 2022, <https://www.rfc-editor.org/rfc/rfc9112>.
[I-D.ietf-lamps-rfc4210bis]
Brockhaus, H., von Oheimb, D., Ounsworth, M., and J. Gray,
"Internet X.509 Public Key Infrastructure -- Certificate
Management Protocol (CMP)", Work in Progress, Internet-
Draft, draft-ietf-lamps-rfc4210bis-07, 19 June 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-lamps-
rfc4210bis-07>.
[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.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/rfc/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.
8.2. Informative References
[RFC9480] Brockhaus, H., von Oheimb, D., and J. Gray, "Certificate
Management Protocol (CMP) Updates", RFC 9480,
DOI 10.17487/RFC9480, November 2023,
<https://www.rfc-editor.org/rfc/rfc9480>.
[RFC9483] Brockhaus, H., von Oheimb, D., and S. Fries, "Lightweight
Certificate Management Protocol (CMP) Profile", RFC 9483,
DOI 10.17487/RFC9483, November 2023,
<https://www.rfc-editor.org/rfc/rfc9483>.
[RFC2510] Adams, C. and S. Farrell, "Internet X.509 Public Key
Infrastructure Certificate Management Protocols",
RFC 2510, DOI 10.17487/RFC2510, March 1999,
<https://www.rfc-editor.org/rfc/rfc2510>.
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[RFC4210] Adams, C., Farrell, S., Kause, T., and T. Mononen,
"Internet X.509 Public Key Infrastructure Certificate
Management Protocol (CMP)", RFC 4210,
DOI 10.17487/RFC4210, September 2005,
<https://www.rfc-editor.org/rfc/rfc4210>.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, DOI 10.17487/RFC4301,
December 2005, <https://www.rfc-editor.org/rfc/rfc4301>.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, August 2008,
<https://www.rfc-editor.org/rfc/rfc5246>.
[RFC6712] Kause, T. and M. Peylo, "Internet X.509 Public Key
Infrastructure -- HTTP Transfer for the Certificate
Management Protocol (CMP)", RFC 6712,
DOI 10.17487/RFC6712, September 2012,
<https://www.rfc-editor.org/rfc/rfc6712>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/rfc/rfc8446>.
[RFC9110] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "HTTP Semantics", STD 97, RFC 9110,
DOI 10.17487/RFC9110, June 2022,
<https://www.rfc-editor.org/rfc/rfc9110>.
Appendix A. History of Changes
Note: This appendix will be deleted in the final version of the
document.
From version 03 -> 04:
* Aligned with released RFC 9480 - RFC 9483.
From version 02 -> 03:
* Fixing one formatting nit.
From version 01 -> 02:
* Updated Section 3.4 including the requirement to add the content-
length filed into the HTTP header.
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* Added a reference to TLS 1.3.
* Addressed idnits feedback, specifically changing the following RFC
references: RFC2616 -> RFC9112; RFC2818 -> RFC9110, and RFC5246 ->
RFC8446
From version 00 -> 01:
* Performed all updates specified in CMP Updates Section 3.
Version 00:
This version consists of the text of RFC6712 with the following
changes:
* Introduced the authors of this document and thanked the authors of
RFC6712 for their work.
* Added a paragraph to the introduction explaining the background of
this document.
* Added the change history to this appendix.
Authors' Addresses
Hendrik Brockhaus
Siemens
Werner-von-Siemens-Strasse 1
80333 Munich
Germany
Email: hendrik.brockhaus@siemens.com
URI: https://www.siemens.com
David von Oheimb
Siemens
Werner-von-Siemens-Strasse 1
80333 Munich
Germany
Email: david.von.oheimb@siemens.com
URI: https://www.siemens.com
Mike Ounsworth
Entrust
1187 Park Place
Minneapolis, MN 55379
United States of America
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Email: mike.ounsworth@entrust.com
URI: https://www.entrust.com
John Gray
Entrust
1187 Park Place
Minneapolis, MN 55379
United States of America
Email: john.gray@entrust.com
URI: https://www.entrust.com
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