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Internet LAMPS Working Group Internet-Draft This document describes an extension to RFC7030, Enrollment over Secure Transport to give an indication to a end-entity device when it should start attempting to renew its certificates. Prior art is that client decides, with a typical recommmendation to start when the remaining lifetime of the certificate is at the 50% point. As typical certificate lifetimes are reduced from years to fractions of a year, the 50% may be far too early, and this document provides a way to give alternate advice. About This Document Status information for this document may be found at . Discussion of this document takes place on the lamps Working Group mailing list (), which is archived at . Subscribe at . Source for this draft and an issue tracker can be found at .

Introduction explains why certificate lifetimes and renewal times need more deterministic control in the ACME ecosystem. Similar arguments apply to the ecosystem. This document extends to add support for renewal information, by adding a new entry to the HTTP URIs for Control list defined in This mechanism enables EST servers to provide suggested detailed renewal operations to EST clients, and enables clients to inform the EST server that they have successfully renewed and replaced a certificate. The /renewal-info URI is added, as an OPTIONAL operation, to the table in figure 5 in section 3.2.2 of .

Terminology 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.

Protocol Details A new magic header will be returned during RFC7030 certificate enrollment, whether using simpleenroll, or fullcmc.

Renewal Information Request To retrieve the renewal information, the EST client uses the following HTTP request-line: GET /.well-known/est/renewal-info/<certificate-id>; The request includes a unique identifier for the certificate in question. The unique identifier is constructed by concatenating the base64url encoding of the keyIdentifier field of the certificate's Authority Key Identifier (AKI) extension, the period character ".", and the base64url encoding of the DER-encoded Serial Number field (without the tag and length bytes). All trailing "=" characters MUST be stripped from both parts of the unique identifier. Thus, the full request URL is constructed as follows (split onto multiple lines for readability), where the "||" operator indicates string concatenation: url = /.well-known/est/renewal-info || '/' || base64url(AKI keyIdentifier) || '.' || base64url(Serial)

Renewal Information Response The structure the EST RenewalInfo object is as follows: suggestedWindow (object, required): A JSON object with two keys, "start" and "end", whose values are timestamps, encoded in the format specified in , which bound the window of time in which the CA recommends renewing the certificate. For example: ``` HTTP/1.1 200 OK Content-Type: application/json Retry-After: 21600 { "suggestedWindow": { "start": "2025-01-02T04:00:00Z", "end": "2025-01-03T04:00:00Z" } } ```

Base64 Not Used mistakenly declared that all content would be base64 encoded. clarifies that the content is to be base64 encoded, whether or not there is a Content-Transfer-Encoding header present. It further clarifies that future extensions (such as this document) will not use base64 encoding. The response detailed above is not base64 encoded.

Renewal Operations Clients MUST attempt renewal at a time of their choosing based on the suggested renewal window, obtained in the previous step. The following algorithm is RECOMMENDED for choosing a renewal time:

1. Select a uniform random time within the suggested window.
2. If the selected time is in the past, attempt renewal immediately.
3. Otherwise, if the client can schedule itself to attempt renewal at exactly the selected time, do so.
4. Otherwise, if the selected time is before the next time that the client would wake up normally, attempt renewal immediately.
5. Otherwise, sleep until the time indicated by the Retry-After header and return to Step 1.

In all cases, renewal attempts are subject to the client's existing error backoff and retry intervals. A RenewalInfo object in which the end timestamp equals or precedes the start timestamp is invalid. Servers MUST NOT serve such a response, and clients MUST treat one as though they failed to receive any response from the server (e.g., retry at an appropriate interval, renew on a fallback schedule, etc.).

Fetching Schedule The advice in applies: Clients SHOULD fetch a certificate's RenewalInfo immediately after issuance. During the lifetime of a certificate, the renewal information needs to be fetched frequently enough that clients learn about changes in the suggested window quickly, but without overwhelming the server. This protocol uses the Retry-After header [RFC9110] to indicate to clients how often to retry. Note that in other HTTP applications, Retry-After often indicates the minimum time to wait before retrying a request. In this protocol, it indicates the desired (i.e., both requested minimum and maximum) amount of time to wait. Clients MUST NOT check a certificate's RenewalInfo after the certificate has expired. Clients MUST NOT check a certificate's RenewalInfo after they consider the certificate to be replaced (for instance, after a new certificate for the same identifiers has been received and configured).

Privacy Considerations A very short certificate lifetime renewal time will cause clients to communicate with the EST Registrar more frequently. EST connections for renewals typically make use of mutually authenticated TLS. When the client certificate being an IDevID, or the last issued certificate, often an LDevID, there is potential to disclose identities during this connection when using TLS 1.2. TLS 1.3 does not suffer from this problem, and it's use is RECOMMENDED as per

Security Considerations Not sure what yet.

IANA Considerations Might need a header allocation

Acknowledgements Many bits of text are taken from .

Changelog

References Normative References This document profiles certificate enrollment for clients using Certificate Management over CMS (CMC) messages over a secure transport. This profile, called Enrollment over Secure Transport (EST), describes a simple, yet functional, certificate management protocol targeting Public Key Infrastructure (PKI) clients that need to acquire client certificates and associated Certification Authority (CA) certificates. It also supports client-generated public/private key pairs as well as key pairs generated by the CA. 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. This document describes the commonly used base 64, base 32, and base 16 encoding schemes. It also discusses the use of line-feeds in encoded data, use of padding in encoded data, use of non-alphabet characters in encoded data, use of different encoding alphabets, and canonical encodings. [STANDARDS-TRACK] This memo profiles the X.509 v3 certificate and X.509 v2 certificate revocation list (CRL) for use in the Internet. An overview of this approach and model is provided as an introduction. The X.509 v3 certificate format is described in detail, with additional information regarding the format and semantics of Internet name forms. Standard certificate extensions are described and two Internet-specific extensions are defined. A set of required certificate extensions is specified. The X.509 v2 CRL format is described in detail along with standard and Internet-specific extensions. An algorithm for X.509 certification path validation is described. An ASN.1 module and examples are provided in the appendices. [STANDARDS-TRACK] This document defines a date and time format for use in Internet protocols that is a profile of the ISO 8601 standard for representation of dates and times using the Gregorian calendar. This document updates RFC 7030: Enrollment over Secure Transport to resolve some errata that were reported and that have proven to cause interoperability issues when RFC 7030 was extended. This document deprecates the specification of "Content-Transfer-Encoding" headers for Enrollment over Secure Transport (EST) endpoints. This document fixes some syntactical errors in ASN.1 that were present. Informative References This document specifies how an Automated Certificate Management Environment (ACME) server may provide suggestions to ACME clients as to when they should attempt to renew their certificates. This allows servers to mitigate load spikes and ensures that clients do not make false assumptions about appropriate certificate renewal periods. Public Key Infrastructure using X.509 (PKIX) certificates are used for a number of purposes, the most significant of which is the authentication of domain names. Thus, certification authorities (CAs) in the Web PKI are trusted to verify that an applicant for a certificate legitimately represents the domain name(s) in the certificate. As of this writing, this verification is done through a collection of ad hoc mechanisms. This document describes a protocol that a CA and an applicant can use to automate the process of verification and certificate issuance. The protocol also provides facilities for other certificate management functions, such as certificate revocation. Akamai Technologies TLS 1.3 use is widespread, it has had comprehensive security proofs, and it improves both security and privacy over TLS 1.2. Therefore, new protocols that use TLS must require TLS 1.3. As DTLS 1.3 is not widely available or deployed, this prescription does not pertain to DTLS (in any DTLS version); it pertains to TLS only. This document updates RFC9325 and discusses post-quantum cryptography and the security and privacy improvements over TLS 1.2 as a rationale for that update.