2024-07-24
The Online Certificate Status Protocol (OCSP) is basically dead now
The (web) TLS news of the time interval is that Let's Encrypt intends to stop doing OCSP more or less as soon as Microsoft will let them. Microsoft matters because they are apparently the last remaining major group that requires Certificate Authorities to support OCSP in order for the CA's TLS root certificates to be supported. This is functionally the death declaration for OCSP, including OCSP stapling.
(The major '(TLS) root programs' are all associated with browsers and major operating systems; Microsoft for Windows and Edge, Apple for macOS, iOS, and Safari, Google for Chrome and Android, and Mozilla for Firefox and basically everyone else.)
Let's Encrypt is only one TLS Certificate Authority so in theory other CAs could keep on providing OCSP. However, LE is the dominant TLS CA, responsible for issuing a very large number of the active TLS certificates, plus CAs don't like doing OCSP anyway because it takes a bunch of resources (since you have to be prepared for a lot of browsers and devices to ask you for the status of things). Also, as a practical matter OCSP has been mostly dead for a long time because Chrome hasn't supported OCSP for years, which means that only a small amount of traffic will be affected by the OCSP status of TLS certificates used for the web (which has periodically led to OCSP breaking and causing problems for people using browsers that do check, like Firefox; I've disabled OCSP in my Firefox profiles for years).
I suspect that Let's Encrypt's timeline of three to six months after Microsoft allows them to stop doing OCSP is better understood as 'one to two Let's Encrypt certificate rollovers', since all of LE's certificates are issued for 90 days. I also suspect that people will have enough problems with web servers (and perhaps client programs) that it will wind up being more toward the six month side.
Personally, I'm glad that OCSP is finally and definitely dying, and not just because I haven't had good experiences with it myself (as a Firefox user; as a website operator we never tried to add OCSP stapling). Regardless of its technical design, OCSP as an idea and a protocol is something that doesn't fit well into the modern Internet and how we understand the political issues involved with Internet-scale things (like how much they cost and who pays for them, what information they leak, what the consequences of an outage are, how much they require changes to slow-moving server software, and so on).