Internet X.509 Public Key Infrastructure -- HTTP Transfer for the Certificate Management Protocol (CMP)

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 June 2025.¶

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 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

[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] requires a 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-, 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 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 as CMP requires connection and error handling from the transfer protocol. All theses 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] 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 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.¶

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]). For details on how to transfer multiple requests see Section 4.11 of [RFC9205].¶

   [15] CA Key Update Announcement
   [16] Certificate Announcement
   [17] Revocation Announcement
   [18] CRL Announcement

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 that led to [RFC6712] might use an unregistered "application/pkixcmp-poll" Media Type. Conforming implementations MAY handle this type like "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] 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 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 reference to this document.¶

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

The reference 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 reference to this document.¶

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

Appendix A. History of Changes

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

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 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