This letter was originally published in our 2024 Annual Report.
The past year at ISRG has been a great one and I couldn’t be more proud of our staff, community, funders, and other partners that made it happen. Let’s Encrypt continues to thrive, serving more websites around the world than ever before...
Lets Encrypt certs tend to be renewed by a cronjob, anyway. The advantage is that if someone gets your cert without your knowledge, they have, at most, six days to make use of it.
If they got it with your knowledge, can’t you just revoke the old one?
Yeah, but unfortunately cert revocation isn't that great in practice. Lots of devices and services don't even check the revocation lists on every connection.
It would be six days at max, assuming they managed to steal the certificate immediately after it was issued, otherwise it's gonna be even less.
Having the certificate doesn't automatically mean you can change the site, if you have control of the site hosting you likely wouldn't need to steal the cert anyway.
Stealing the certificate would allow you to run a man in the middle type attack but that's inevitably going to be very limited in scope. The shorter time limit on the cert reduces that scope even further, which is great.
Since most Let's Encrypt certs will have an automated renewal process this doesn't even really change the overhead of setup so I think this move makes a lot of sense.
There are other things certificates can be used for as well of course but I'm just going off your example.