Seems rather problematic that a cert that appears to have been revoked 5 days ago isn’t recognized as revoked by virtually any browser. Is this an OCSP-related issue or do browsers actually do a bad job at checking for revocation?
The idea with OCSP-stapling is that the webserver fetches the OCSP data, caches it for TTL ~24 hours, and staples it to the HTTPS handshake. That way, the browser does not need to query the issuer's OCSP servers, avoiding both performance and privacy concerns. Revoked certificates will continue to work for up to 24 hours, but that, IMO, is within an accepted range compared to CRL that can take a lot longer.
The downside is that the HTTPS handshakes now contain a bit more data, and we want to keep this as minimal as possible.
The problem with OCSP stapling is that it either the client has to fall back to doing OCSP checking itself if the server doesn't staple the signature, which has its own problems[1], or enough servers need to support ocsp stapling that the client can just reject connections that don't include it. And unfortunately, there was never a significant uptake for servers, partly because there wasn't really any incentive to implement OCSP stapling. Maybe if there was a TLS 2.0 (or some other standard) that required OCSP stapling and had other benefits as well, it could work.
[1]: the biggest problem with non-stapled OCSP is what to do if you don't get a response for the ocsp request. If you fail open, an attacker can intercept the request to prevent you from knowing the cert is revoked, but if you fail closed, then any issue with the connection to the ocsp server results in loss of service. And then there are also issues with additional latency to wait for the ocsp response, privacy leaks from the ocsp requests, etc.
web servers can refresh OCSP responses in the background and cache valid responses to add some tolerance against temporarily downtimes in the OCSP server.
It's really a chicken and egg problem. Browsers don't want to support must-staple because not enough servers use it. And servers don't use it, because browsers don't require it (or even implement it). And now CAs don't support it, because hardly anyone was using it.
Now if CAs started requiring must-staple, that might push it into widespread use. But that would cause a lot of disruption.
As for server implementaions. Most servers, sure it isn't that much harder to use `must-staple`, if you are already doing ocsp stapling. But most servers don't do the stapling at all, because there isn't a strong reason to, and you need to set up a system to periodically fetch and cache the OCSP signatures, and whatever system you use to terminate TLS needs to support it.
- Let's Encrypt: doesn't support it since May 7 this year
- Buy Pass: No longer offers free certificates, probably didn't have must-staple either
- Zero SSL, I didn't find any public links to check if they sign CSRs with it.
- Google Trust Services: Same as above
- Amazon Trust: Same as above, but it probably does.
Short lived certificates are definitely the better way forward.
24 hour certificates will add a significantly more load on CAs, a lot more than maintaining an OCSP responder.
We're starting to see adoption for O(days) now but I imagine that the lifetime will continue to decrease to some minimum O(hours) in the years to come.
IETF will be gradually reducing maximum length of public certs to 47 days. I expect this will help some of the issue since expired certs can be removed from the list.
Compared to what? 12MB JavaScript bundles and autoplay videos? Do CDNs still exist?
There's a finite number of CAs and browsers can be expected to perform caching. Delta CRLs also exist and the CAs can decline to include expired leaf certs.
This sounds like a made up problem that was solved 25 years ago.
Not really sure how big of a problem a list could be?
And if I cache the information that it is revoked, how do I know that it's allowed again?
I could check, let's say one time per day even if I don't access that site.
In any case I'm still leaking which domains I browse and I keep trusting cached certificates until the next check.
On the other side, with short lived certificates I would be trusting a certificate for a longer time, until it expires.
Downloading a list of all certificates and their status from every CAs is probably unfeasible.
It seems that we can't escape a tradeoff between privacy and security.
How do you know it is allowed again? Because it responds with a new certificate, that isn't revoked...
You are not leaking anything. You are just downloading a list of revoked domains. Regardless of whether you are visiting them or not.