4 ms·

But certificates expire for a reason, don't they? The idea is that with enough time, the key could be cracked.

cerved 3y ago
The reason is money. Sweet, delicious money
allset_ 3y ago
The more pressing reason they expire for web sites is that site ownership can change and you don't want someone else having an infinite lifetime cert for a domain you just bought. It's also useful to issue short lived certs and use the expiry date to handle revocation rather than maintaining a CRL.
cortesoft 3y ago
That isn’t why certs expire. If a hacker could crack the key in some time that is longer than the expiry but short enough to be a threat, they could instead just spend that time cracking the signing key that verifies the cert signature… then, the hacker could generate as many trusted certs as they want for for any domain.
- oasisbob 3y ago
  That's exactly why SHA1 was deprecated in TLS certs. https://security.googleblog.com/2015/12/an-update-on-sha-1-certificates-in.html https://security.googleblog.com/2015/12/an-update-on-sha-1-c... Even OCSP was affected: https://cabforum.org/2022/01/26/ballot-sc53-sunset-for-sha-1-ocsp-signing/ https://cabforum.org/2022/01/26/ballot-sc53-sunset-for-sha-1...
  - cortesoft 3y ago
    I wasn't trying to say that brute force wasn't a risk, just that it wasn't why certainly expire
AtNightWeCode 3y ago
No.
- AtNightWeCode 3y ago
  The reason certificates expire is because historically the quality of the generators was known to be poor. NotAfter ensures that a new certificate is created with a better generator every now and then. Today that is not really a problem. Public CAs are not very secure as NSA proved and I am not sure why there is no better alternative yet.
oasisbob 3y ago
Or, the private key could leak. Or, the cert could have been issued by an authority which issued the cert despite compliance problems. Web PKI is different than code signing, but if you look at the discussions within the CAB forum, there are very good reasons to limit certificate lifetime.

The reason is money. Sweet, delicious money

The more pressing reason they expire for web sites is that site ownership can change and you don't want someone else having an infinite lifetime cert for a domain you just bought. It's also useful to issue short lived certs and use the expiry date to handle revocation rather than maintaining a CRL.

cortesoft 3y ago

That isn’t why certs expire. If a hacker could crack the key in some time that is longer than the expiry but short enough to be a threat, they could instead just spend that time cracking the signing key that verifies the cert signature… then, the hacker could generate as many trusted certs as they want for for any domain.

oasisbob 3y ago
That's exactly why SHA1 was deprecated in TLS certs. https://security.googleblog.com/2015/12/an-update-on-sha-1-certificates-in.html https://security.googleblog.com/2015/12/an-update-on-sha-1-c... Even OCSP was affected: https://cabforum.org/2022/01/26/ballot-sc53-sunset-for-sha-1-ocsp-signing/ https://cabforum.org/2022/01/26/ballot-sc53-sunset-for-sha-1...
- cortesoft 3y ago
  I wasn't trying to say that brute force wasn't a risk, just that it wasn't why certainly expire

AtNightWeCode 3y ago

No.

AtNightWeCode 3y ago
The reason certificates expire is because historically the quality of the generators was known to be poor. NotAfter ensures that a new certificate is created with a better generator every now and then. Today that is not really a problem. Public CAs are not very secure as NSA proved and I am not sure why there is no better alternative yet.

oasisbob 3y ago

Or, the private key could leak. Or, the cert could have been issued by an authority which issued the cert despite compliance problems. Web PKI is different than code signing, but if you look at the discussions within the CAB forum, there are very good reasons to limit certificate lifetime.