wdiff rfc9811.original rfc9811.txt

LAMPS Working Group

Internet Engineering Task Force (IETF) H. Brockhaus
Internet-Draft
Request for Comments: 9811 D. von Oheimb
Obsoletes: 6712 6712, 9480 (if approved) Siemens
Intended status:
Category: Standards Track M. Ounsworth
Expires: 13 July 2025
ISSN: 2070-1721 J. Gray
Entrust
9 January
July 2025

Internet X.509 Public Key Infrastructure -- HTTP Transfer for the
Certificate Management Protocol (CMP)
draft-ietf-lamps-rfc6712bis-10

Abstract

This document describes how to layer the Certificate Management
Protocol (CMP) over HTTP.

It includes the updates to RFC 6712 specified in RFC 9480 Section 3.
These 3 of RFC
9480; these updates introduce CMP URIs using a Well-known well-known prefix. It
obsoletes RFC 6712 and 6712; and, together with I-D.ietf-lamps-rfc4210bis and RFC 9810, it also obsoletes
RFC 9480.

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 an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force
(IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list It represents the consensus of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid the IETF community. It has
received public review and has been approved for a maximum publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.

Information about the current status of six months this document, any errata,
and how to provide feedback on it may be updated, replaced, or obsoleted by other documents obtained 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 13 July 2025.
https://www.rfc-editor.org/info/rfc9811.

This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info)
(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 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 Made by RFC 9480 . . . . . . . . . . . . . . . . 4
1.2. Changes Made by This Document . . . . . . . . . . . . . . 4
2. Conventions Used in This Document . . . . . . . . . . . . . . 4
3. HTTP-Based Protocol . . . . . . . . . . . . . . . . . . . . . 4
3.1. General Form . . . . . . . . . . . . . . . . . . . . . . 5
3.2. Media Type . . . . . . . . . . . . . . . . . . . . . . . 5
3.3. Communication Workflow . . . . . . . . . . . . . . . . . 5
3.4. HTTP Request-URI . . . . . . . . . . . . . . . . . . . . 6
3.5. Pushing of Announcements . . . . . . . . . . . . . . . . 6
4. Implementation Considerations . . . . . . . . . . . . . . . . 7
5. Security Considerations . . . . . . . . . . . . . . . . . . . 8
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
8.1.
7.1. Normative References . . . . . . . . . . . . . . . . . . 9
8.2.
7.2. Informative References . . . . . . . . . . . . . . . . . 10
Appendix A. History of Changes . . . . . . . . . . . . . . . . . 11
Acknowledgements
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13

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.

]

The Certificate Management Protocol (CMP) [I-D.ietf-lamps-rfc4210bis] [RFC9810] requires a well-defined well-
defined transfer mechanism to enable End Entities (EEs), Registration
Authorities (RAs), and Certification Authorities (CAs) to pass
PKIMessage structures 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-, email-, and
HTTP-based transfer, but those were not specified in detail.

Since the second version of the CMP specification [RFC4210]
incorporated its own polling mechanism and thus mechanism, 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 reliable transport transport, as CMP it requires
connection and error handling from the transfer protocol. All these
features are 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 (e.g., HTTP/1.1 as specified in [RFC9110] and
[RFC9112]) for transferring CMP messages exclusively uses the POST
method for requests, effectively tunneling CMP over HTTP. While this
is generally considered bad practice (see BCP 56 [RFC9205] RFC 9205 [BCP56] for best
current practice on building protocols with HTTP) 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 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.

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 identification (transactionID),
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 Made by RFC 9480

CMP Updates [RFC9480] updated Section 3.6 of [RFC6712], supporting
the PKI management operations specified in the Lightweight CMP
Profile [RFC9483], in the following areas:

* Introduce Introduced the HTTP URI path prefix '/.well-known/cmp'.

* Add Added options for extending the URI structure with further
segments and define defined a new protocol registry group to that aim.

1.2. Changes Made by This Document

This document obsoletes [RFC6712]. It includes the changes specified
in Section 3 of [RFC9480] [RFC9480], as described in Section 1.1 of this
document. Additionally, it adds the following changes:

* Removed the requirement to support HTTP/1.0 [RFC1945] in
accordance with Section 4.1 of [RFC9205].

* Implementations MUST forward CMP messages when an HTTP error
status code occurs, occurs; see Section 3.1.

* Removed Section 3.8 of [RFC6712] as it contains information
redundant with current HTTP specification.

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 [RFC9293] is available, HTTP [RFC9110]
SHOULD be utilized for conveying CMP messages. This specification
requires using the POST method (Section 3.1) and the "Content-Type"
header field (Section 3.2), which are available since HTTP/1.0
[RFC1945].

Note: In some situations, CMP requires multiple request/response
pairs to perform a PKI management operation. Their affiliation with
a PKI management operation is indicated by a transaction identifier
in the CMP message header (see transactionID described in
Section 5.1.1 of [I-D.ietf-lamps-rfc4210bis]). [RFC9810]). For details on how to transfer multiple requests
requests, see Section 4.11 of [RFC9205].

3.1. General Form

A DER-encoded [ITU.X690.1994] PKIMessage (Section 5.1 of
[I-D.ietf-lamps-rfc4210bis]) [RFC9810])
MUST be sent as the content of an HTTP POST request. If this HTTP
request is successful, the server returns the CMP response in the
content of the HTTP response. The HTTP response status code in this
case MUST be 200 (OK) status code; (OK); other Successful 2xx status codes MUST NOT be
used for this purpose. HTTP responses to pushed CMP announcement
messages described in Section 3.5 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, the 301 (Moved Permanently)
status code 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. Whenever a client
receives an HTTP response with a status code in the 2xx, 4xx, or 5xx
ranges, it MUST support handling response message content containing
a CMP response PKIMessage.

3.2. Media Type

The Internet Media Type media type "application/pkixcmp" MUST be set in the HTTP
"Content-Type" header field when conveying a PKIMessage.

3.3. 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 3.5 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.

3.4. 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.

CMP clients have 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, 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>. The following list shows examples of
valid full CMP URIs:

* 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>

Note that https can also be used instead of http, http; see item 5 in the
Security Considerations (Section 5).

3.5. 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, Certificate Revocation List (CRL), a PKI Information
Request using a General Message general message as described in Appendix D.5 of [I-D.ietf-lamps-rfc4210bis]
[RFC9810] can be used.

When pushing announcement messages, PKIMessage structures MUST be
sent as the content 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 3.4.

The following types of PKIMessage are announcements that may be
pushed by a CA. The prefixed numbers reflect ASN.1 tags of the
PKIBody structure (Section 5.1.2 of [I-D.ietf-lamps-rfc4210bis]). [RFC9810]).

[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 content. 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 content.

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.

A receiver MUST answer with a suitable 4xx or 5xx error code when a
problem occurs.

4. Implementation Considerations

Implementers should be aware that other implementations might exist
that use a different approach for transferring CMP over HTTP.
Further, implementations based on earlier I-Ds documents that led to
[RFC6712] might use an unregistered "application/pkixcmp-poll" Media Type. media
type. Conforming implementations MAY handle this type like "application/
pkixcmp".
"application/pkixcmp".

5. Security Considerations

All security considerations in HTTP [RFC9110] apply. The following
items 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.

2. Without being encapsulated in effective security protocols, such
as Transport Layer Security (TLS) [RFC5246] or [RFC8446], or without
using HTTP digest [RFC9530] [RFC9530], there is no integrity protection at
the HTTP level. Therefore, information from the HTTP should not
be used to change state of the transaction, regardless of whether
any mechanism was used to ensure the authenticity or integrity of
HTTP messages (e.g., TLS or HTTP digests).

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 meddler-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 personal, technical, or business critical business-critical
information. The protection of the confidentiality of CMP
messages together with an initial authentication of the RA/CA
before the first CMP message is transmitted ensures the privacy
of the EE requesting certificates. Therefore, users of the HTTP
transfer for CMP messages should consider using HTTP over TLS
according to [RFC9110] or using virtual private networks created,
for example, by utilizing Internet Protocol Security according to
[RFC7296].

6. IANA Considerations

The reference to [RFC2510] at https://www.iana.org/assignments/media-
types/media-types.xhtml should be replaced with a

IANA has made the following updates:

* the reference for "application/pkixcmp" in the "Media Types"
registry <https://www.iana.org/assignments/media-types> refers to
this
document.

The reference to [RFC4210] at https://www.iana.org/assignments/core-
parameters/core-parameters.xhtml should be replaced with a document, instead of [RFC2510].

* the reference for "application/pkixcmp" in the "CoAP Content-
Formats" registry <https://www.iana.org/assignments/core-
parameters> refers to this document.

The document, instead of [RFC4210].

* the reference for "cmp" in the "Well-Known URIs" registry
<https://www.iana.org/assignments/core-parameters> refers to [RFC9480] at https://www.iana.org/assignments/well-
known-uris/well-known-uris.xhtml and
https://www.iana.org/assignments/cmp/cmp.xhtmlshould should be
replaced with a this
document instead of [RFC4210].

* the reference for "p" in the "CMP Well-Known URI Path Segments"
registry <https://www.iana.org/assignments/cmp> refers to this document.
document instead of [RFC9480].

No further action by the IANA is necessary for this document or any
anticipated updates.

7. Acknowledgments

The authors wish to thank Tomi Kause and Martin Peylo, the original
authors of [RFC6712], for their work.

We also thank all reviewers for their valuable feedback.

8. References

8.1.

7.1. 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>.
<https://www.rfc-editor.org/info/rfc1945>.

[RFC8615] Nottingham, M., "Well-Known Uniform Resource Identifiers
(URIs)", RFC 8615, DOI 10.17487/RFC8615, May 2019,
<https://www.rfc-editor.org/rfc/rfc8615>.
<https://www.rfc-editor.org/info/rfc8615>.

[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>.
<https://www.rfc-editor.org/info/rfc9110>.

[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] <https://www.rfc-editor.org/info/rfc9112>.

[RFC9810] 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-15, 18 November 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-lamps-
rfc4210bis-15>. RFC 9810,
DOI 10.17487/RFC9810, July 2025,
<https://www.rfc-editor.org/info/rfc9810>.

[ITU.X690.1994]
International Telecommunications Union,
ITU-T, "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. 1994,
<https://www.itu.int/rec/T-REC-X.690-199407-S/en>.

[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>.
<https://www.rfc-editor.org/info/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. <https://www.rfc-editor.org/info/rfc8174>.

7.2. 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>.
<https://www.rfc-editor.org/info/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>.
<https://www.rfc-editor.org/info/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>.
<https://www.rfc-editor.org/info/rfc2510>.

[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>.
<https://www.rfc-editor.org/info/rfc4210>.

[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>.
<https://www.rfc-editor.org/info/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>.
<https://www.rfc-editor.org/info/rfc6712>.

[RFC7296] Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T.
Kivinen, "Internet Key Exchange Protocol Version 2
(IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October
2014, <https://www.rfc-editor.org/rfc/rfc7296>. <https://www.rfc-editor.org/info/rfc7296>.

[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>.
<https://www.rfc-editor.org/info/rfc8446>.

[RFC9530] Polli, R. and L. Pardue, "Digest Fields", RFC 9530,
DOI 10.17487/RFC9530, February 2024,
<https://www.rfc-editor.org/rfc/rfc9530>.

[RFC9205]
<https://www.rfc-editor.org/info/rfc9530>.

[BCP56] Best Current Practice 56,
<https://www.rfc-editor.org/info/bcp56>.
At the time of writing, this BCP comprises the following:

Nottingham, M., "Building Protocols with HTTP", BCP 56,
RFC 9205, DOI 10.17487/RFC9205, June 2022,
<https://www.rfc-editor.org/rfc/rfc9205>.
<https://www.rfc-editor.org/info/rfc9205>.

[RFC9293] Eddy, W., Ed., "Transmission Control Protocol (TCP)",
STD 7, RFC 9293, DOI 10.17487/RFC9293, August 2022,
<https://www.rfc-editor.org/rfc/rfc9293>.

Appendix A. History of Changes

Note: This appendix will be deleted in the final version of the
document.

From version 09 -> 10:

* Addressed IESG review comments from Mahesh Jethanandani and
responded to comments from Orie Steele and Zaheduzzaman Sarker via
email

From version 08 -> 09:

* Incorporated relevant text from former Sections 3.1 and 3.2 in the
introduction of Section 3 as proposed by HTTPDIR review
* Added reference to HTTP Security Considerations to Section 5 and
updated the first item as proposed by HTTPDIR review

From version 07 -> 08:

* Addressed HTTPDIR, SECDIR, OPSDIR and ARTART review comments

* Aligned the terminology with https://httpwg.org/admin/editors/
style-guide

* Implemented editorial changes proposed by OPSDIR reviewer

* Removed requirement to support HTTP/1.0

* Added normative language in Sections 3.3 and 3.7 for clarity

* Added the requirement to provide any HTTP response message content
to the application

* Removed the paragraph on the "Content-Length" header field and
Section 3.8 to reduce redundancy with current versions HTTP/1.1

From version 06 -> 07:

* Updated the the page header to 'HTTP Transfer for CMP'

* Removed one instruction to RFC Editors

* Deprecated PKIMessages as plural of PKIMessage to prevent
confusion with ASN.1 type PKIMessages

* Fixed some nits in Section 1

* Aligned Section 3.6 and Section 5 with RFC 9483 and draft-ietf-
anima-brski-ae

From version 05 -> 06:

* Updates IANA considerations addressing IANA early review (see
thread "[IANA #1368693] Early review: draft-ietf-lamps-
rfc4210bis-12 (IETF 120)").

From version 04 -> 05:

* Added IANA considerations addressing IANA early review.

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.

* 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
<https://www.rfc-editor.org/info/rfc9293>.

Acknowledgements

The authors of this document wish to thank Tomi Kause and thanked Martin Peylo, the original
authors of
RFC6712 [RFC6712], for their work.

* Added a paragraph to the introduction explaining the background of
this document.

* Added the change history to this appendix.

We also thank all reviewers for their valuable feedback.

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
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