Let’s Encrypt will be reducing the validity period of the certificates we issue. We currently issue certificates valid for 90 days, which will be cut in half to 45 days by 2028.
This change is being made along with the rest of the industry, as required by the CA/Browser Forum Baseline Requirements, which set the technical requirements that we must follow. All publicly-trusted Certificate Authorities like Let’s Encrypt will be making similar changes. Reducing how long certificates are valid for helps improve the security of the internet, by limiting the scope of compromise, and making certificate revocation technologies more efficient.
Terminology: revoked means the issuer of the certificate has decided that the certificate should not be trusted anymore even though it is still valid.
If a attacker gets access to a certificates key, they can impersonate the server until the validity period of the cert runs out or it is revoked by the CA. However … revocation doesn’t work. The revocation lists arent checked by most clients so a stolen cert will be accepted potentially for a very long time.
The second argument for shorter certs is adoption of new technology so certs with bad cryptographic algorithms are circled out quicker.
And third argument is: if the validity is so short you don’t want to change the certs manually and automate the process, you can never forget and let your certs expire.
We will probably get to a point of single day certs or even one cert per connection eventually and every step will be saver than before (until we get to single use certs which will probably fuck over privacy)