[nightpool]

No, they're not useless at all. The point of shortening certificate periods is that companies complain when they have to put customers on revocation lists, because their customers need ~2 years to update a certificate. If CRLs were useless, nobody would complain about being put on them. If you follow the revocation tickets in ca-compliance bugzilla, this is the norm—not the exception. Nobody wants to revoke certificates because it will break all of their customers. Shortening the validity period means that CAs and users are more prepared for revocation events.

[pas]

... what are the revocation tickets about then? how is it even a question whether to put a cert on the CRL? either the customer wants to or the key has been compromised? (in which case the customer should also want to have it revoked ASAP, no?)

can you elaborate on this a bit? thank you!

[crote]

> what are the revocation tickets about then

Usually, technical details. Think: a cert issued with a validity of exactly 1000 days to the second when the rules say the validity should be less than 1000 days. Or, a cert where the state name field contains its abbreviation rather than the full name. The WebPKI community is rather strict about this: if it doesn't follow the rules, it's an invalid cert, and it MUST be revoked. No "good enough" or "no real harm done, we'll revoke it in three weeks when convenient".

> either the customer wants to or the key has been compromised

The CA wants to revoke, because not doing so risks them being removed from the root trust stores. The customer doesn't want to revoke, because to them the renewal process is a massive inconvenience and there's no real risk of compromise.

This results in CAs being very hesitant to revoke because major enterprise / government customers are threatening to sue and/or leave if they revoke on the required timeline. This in turn shows the WebPKI community that CAs are fundamentally unable to deal with mass revocation events, which means they can't trust that CAs will be able to handle a genuinely harmful compromise properly.

By forcing an industry-wide short cert validity you are forcing large organizations to also automate their cert renewal, which means they no longer pose a threat during mass revocation events. No use threatening your current CA when all of its competitors will treat you exactly the same...

[bombcar]

From my experience the biggest complaints/howlings are when the signing key is compromised; e.g., your cert is valid and fine, but the authority screwed up and so they had to revoke all certs signed with their key because that leaked.

E.g., collateral damage.

[nightpool]

Sure, happy to. The average revocation ticket is something like https://bugzilla.mozilla.org/show_bug.cgi?id=1892419 or https://bugzilla.mozilla.org/show_bug.cgi?id=1624527. The CA shipped some kind of bug leading to noncompliance with baseline requirements. This could be anything from e.g. not validating the email address properly, inappropriately using a third-party resolver to fetch DNS names, or including some kind of extra flag set that they weren't supposed to have set. The CA doesn't want to revoke these certificates, because that would cause customers to complain:

    In response to this incident of mistaken issuance, the verification targets are all government units and government agency websites. We have assessed that the cause of this mis-issuance does not involve a key issue, but only a certificate field issue, which will not affect the customer's information security. In addition, in accordance with the administrative efficiency of government agencies, from notification to the start of processing, it requires agency supervisors at all levels. Signing and approval, and some public agencies need to find information vendors for processing, so it is difficult to complete the replacement within 5 days. Therefore, the certificate is postponed and revoked within a time limit so that the certificates of all websites can be updated smoothly.

[...]

    In this project we plan to initially issue new certificates using the same keys for users to install, and then revoke the old certificates. As these are official government websites, and considering the pressure from government agencies and public opinion, we cannot immediately revoke all certificates without compromising security. Doing so would quickly become news, and we would face further censure from government authorities.

The browsers want them to revoke the certificates immediately, because they rely on CAs to agree to the written requirements of the policy. If you issue certificates, you must validate them in precisely this way, and you must generate certificates with precisely these requirements. The CAs agree in their policies to revoke within 24 hours (serious) or 120 hours (less serious) any certificates issued that violate policy.

And yet when push comes to shove, certificates don't actually get revoked. Everybody has critical clients who pay them $$$$$ and no CAs actually want to make those clients mad. Browsers very rarely revoke certificates themselves, and realistically their only lever is to trust or distrust a CA—they need to rely on the CA to be truthful and manage their own certificates properly. They don't know exactly all of which certificates would be subject to an incident, they don't want to punish CAs for disclosing info publicly, etc. So instead, they push for systematic changes that will make it easier for CAs to revoke certificates in the future, including ACME ARI and shorter certificate lifetimes.

[pas]

Thank you for the detailed answer!

It's unacceptable that operational matters are not handled by a standing ops team that covers so and so gov agencies.

(And at least Apple did something useful by pushing for shorter validity time for certs.)

[nightpool]

Yes, everyone in the WebPKI community is pushing for shorter validity lifetime. But as you can see in the parent thread here ("Which is yet another chore. And it doesn’t add any security"), everybody is mad that browsers are pushing for shorter certificate lifetimes.