can you elaborate on this a bit? thank you!
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...
E.g., collateral damage.
And a short expiration time absolutely increases security by reducing attack surface.
expired letsencrypt cert on a raspberrypi at home smells of not paying attention... with governments, there are many, many points of failure.
use cloudflare, never think about it.
or
use certbot, never think about it.
Hand over our private keys to a third party or run this binary written by some volunteers in some basements who will not sign a support contract with us...
The whole point was to force automation, and if corps want to be stubborn that's no skin of my back, the shorter durations are coming regardless.
Yes, its to make it so that a dedicated effort to break the key has it rotated before someone can impersonate it... its also a question of how big is the historical data window that an attacker has i̶f̶ when someone cracks the key?