]> Siemens

Werner-von-Siemens-Strasse 1 Munich 80333 Germany hendrik.brockhaus@siemens.com https://www.siemens.com

Siemens

Werner-von-Siemens-Strasse 1 Munich 80333 Germany david.von.oheimb@siemens.com https://www.siemens.com

Entrust

1187 Park Place Minneapolis MN 55379 United States of America mike.ounsworth@entrust.com https://www.entrust.com

Entrust

1187 Park Place Minneapolis MN 55379 United States of America john.gray@entrust.com https://www.entrust.com

sec LAMPS Working Group CMP HTTP Certificate management PKI 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.

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) 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 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 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 extends the polling mechanism specified in the second version of CMP 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. 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.

Changes Made by RFC 9480 CMP Updates updated , supporting the PKI management operations specified in the Lightweight CMP Profile , 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.

Changes Made by This Document This document obsoletes RFC 6712. It includes the changes specified by CMP Updates Section 3 as described in and added the requirement on providing the Content-Length header field in .

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 when, and only when, they appear in all capitals, as shown here.

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.

HTTP Versions Implementations MUST support HTTP/1.0 and SHOULD support HTTP/1.1 .

Persistent Connections HTTP persistent connections 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.

General Form A 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 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 , "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.

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 PKIMessage.

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 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.

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 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, 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 , 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>

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 D.5 of 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 . The following types of PKIMessage are announcements that may be pushed by a CA. The prefixed numbers reflect ASN.1 numbering of the respective element. 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. A receiver MUST answer with a suitable 4xx or 5xx HTTP error code when a problem occurs.

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 . 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.

Implementation Considerations Implementors should be aware that implementations might exist that use a different approach for transferring CMP over HTTP, because RFC 6712 has been under development for more than a decade. Further, implementations based on earlier drafts of RFC 6712 might use an unregistered "application/pkixcmp-poll" MIME type.

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 with PKIStatus other than "waiting", 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) or , 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 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 messages might want to consider using HTTP over TLS according to or virtual private networks created, for example, by utilizing Internet Protocol Security according to .

IANA Considerations The reference to at https://www.iana.org/assignments/media-types/media-types.xhtml should be replaced with a reference to this document. The reference to at https://www.iana.org/assignments/core-parameters/core-parameters.xhtml should be replaced with a reference to this document. The reference to 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.

Acknowledgments The authors of this document wish to thank Tomi Kause and Martin Peylo, the original authors of , for their work. We also thank all reviewers of this document for their valuable feedback.

References Normative References The Hypertext Transfer Protocol (HTTP) is an application-level protocol with the lightness and speed necessary for distributed, collaborative, hypermedia information systems. This memo provides information for the Internet community. This memo does not specify an Internet standard of any kind. This memo defines a path prefix for "well-known locations", "/.well-known/", in selected Uniform Resource Identifier (URI) schemes. In doing so, it obsoletes RFC 5785 and updates the URI schemes defined in RFC 7230 to reserve that space. It also updates RFC 7595 to track URI schemes that support well-known URIs in their registry. The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document specifies the HTTP/1.1 message syntax, message parsing, connection management, and related security concerns. This document obsoletes portions of RFC 7230. Siemens Siemens Entrust Entrust This document describes the Internet X.509 Public Key Infrastructure (PKI) Certificate Management Protocol (CMP). Protocol messages are defined for X.509v3 certificate creation and management. CMP provides interactions between client systems and PKI components such as a Registration Authority (RA) and a Certification Authority (CA). This document obsoletes RFC 4210 by including the updates specified by CMP Updates RFC 9480 Section 2 and Appendix A.2 maintaining backward compatibility with CMP version 2 wherever possible and obsoletes both documents. Updates to CMP version 2 are: improving crypto agility, extending the polling mechanism, adding new general message types, and adding extended key usages to identify special CMP server authorizations. Introducing CMP version 3 to be used only for changes to the ASN.1 syntax, which are: support of EnvelopedData instead of EncryptedValue, hashAlg for indicating a hash AlgorithmIdentifier in certConf messages, and RootCaKeyUpdateContent in ckuann messages. In addition to the changes specified in CMP Updates RFC 9480 this document adds support for management of KEM certificates. International Telecommunications Union In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. Informative References This document contains a set of updates to the syntax of Certificate Management Protocol (CMP) version 2 and its HTTP transfer mechanism. This document updates RFCs 4210, 5912, and 6712. The aspects of CMP updated in this document are using EnvelopedData instead of EncryptedValue, clarifying the handling of p10cr messages, improving the crypto agility, as well as adding new general message types, extended key usages to identify certificates for use with CMP, and well-known URI path segments. CMP version 3 is introduced to enable signaling support of EnvelopedData instead of EncryptedValue and signal the use of an explicit hash AlgorithmIdentifier in certConf messages, as far as needed. This document aims at simple, interoperable, and automated PKI management operations covering typical use cases of industrial and Internet of Things (IoT) scenarios. This is achieved by profiling the Certificate Management Protocol (CMP), the related Certificate Request Message Format (CRMF), and transfer based on HTTP or Constrained Application Protocol (CoAP) in a succinct but sufficiently detailed and self-contained way. To make secure certificate management for simple scenarios and constrained devices as lightweight as possible, only the most crucial types of operations and options are specified as mandatory. More specialized or complex use cases are supported with optional features. This document describes the Internet X.509 Public Key Infrastructure (PKI) Certificate Management Protocols. [STANDARDS-TRACK] This document describes the Internet X.509 Public Key Infrastructure (PKI) Certificate Management Protocol (CMP). Protocol messages are defined for X.509v3 certificate creation and management. CMP provides on-line interactions between PKI components, including an exchange between a Certification Authority (CA) and a client system. [STANDARDS-TRACK] This document describes an updated version of the "Security Architecture for IP", which is designed to provide security services for traffic at the IP layer. This document obsoletes RFC 2401 (November 1998). [STANDARDS-TRACK] This document specifies Version 1.2 of the Transport Layer Security (TLS) protocol. The TLS protocol provides communications security over the Internet. The protocol allows client/server applications to communicate in a way that is designed to prevent eavesdropping, tampering, or message forgery. [STANDARDS-TRACK] This document describes how to layer the Certificate Management Protocol (CMP) over HTTP. It is the "CMPtrans" document referenced in RFC 4210; therefore, this document updates the reference given therein. [STANDARDS-TRACK] This document specifies version 1.3 of the Transport Layer Security (TLS) protocol. TLS allows client/server applications to communicate over the Internet in a way that is designed to prevent eavesdropping, tampering, and message forgery. This document updates RFCs 5705 and 6066, and obsoletes RFCs 5077, 5246, and 6961. This document also specifies new requirements for TLS 1.2 implementations. The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document describes the overall architecture of HTTP, establishes common terminology, and defines aspects of the protocol that are shared by all versions. In this definition are core protocol elements, extensibility mechanisms, and the "http" and "https" Uniform Resource Identifier (URI) schemes. This document updates RFC 3864 and obsoletes RFCs 2818, 7231, 7232, 7233, 7235, 7538, 7615, 7694, and portions of 7230.

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