rfc9773v3.txt   rfc9773.txt 
Internet Engineering Task Force (IETF) A. Gable Internet Engineering Task Force (IETF) A. Gable
Request for Comments: 9773 Internet Security Research Group Request for Comments: 9773 Internet Security Research Group
Category: Standards Track May 2025 Category: Standards Track June 2025
ISSN: 2070-1721 ISSN: 2070-1721
ACME Renewal Information (ARI) Extension ACME Renewal Information (ARI) Extension
Abstract Abstract
This document specifies how an Automated Certificate Management This document specifies how an Automated Certificate Management
Environment (ACME) server may provide suggestions to ACME clients as Environment (ACME) server may provide suggestions to ACME clients as
to when they should attempt to renew their certificates. This allows to when they should attempt to renew their certificates. This allows
servers to mitigate load spikes and ensures that clients do not make servers to mitigate load spikes and ensures that clients do not make
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query parameters in its cache key, instituting IP-based rate limits, query parameters in its cache key, instituting IP-based rate limits,
or other general best-practice measures. or other general best-practice measures.
Note that this protocol could exhibit undesired behavior in the Note that this protocol could exhibit undesired behavior in the
presence of significant clock skew between the ACME client and presence of significant clock skew between the ACME client and
server. For example, if a server places the suggested renewal window server. For example, if a server places the suggested renewal window
wholly in the past to encourage a client to renew immediately, a wholly in the past to encourage a client to renew immediately, a
client with a sufficiently slow clock might nonetheless see the client with a sufficiently slow clock might nonetheless see the
window as being in the future. Similarly, a server that wishes to window as being in the future. Similarly, a server that wishes to
schedule renewals very precisely may have difficulty doing so if some schedule renewals very precisely may have difficulty doing so if some
clients have skewed clocks (or do no implement ARI at all). Server clients have skewed clocks (or do not implement ARI at all). Server
operators should take this concern into account when setting operators should take this concern into account when setting
suggested renewal windows. However, many other protocols (including suggested renewal windows. However, many other protocols (including
TLS handshakes themselves) fall apart with sufficient clock skew, so TLS handshakes themselves) fall apart with sufficient clock skew, so
this is not unique to this protocol. this is not unique to this protocol.
7. IANA Considerations 7. IANA Considerations
7.1. ACME Resource Type 7.1. ACME Resource Type
IANA has added the following entry to the "ACME Resource Types" IANA has added the following entry to the "ACME Resource Types"
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