See title. Are there any sources where there are recommended validity times of certificates (based on length, algo, etc)?
I'm particularly interested in validity of RSA certificates...
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There's some info in the Microsoft blog:
Key length of 1024: Validity period = not greater than 6-12 months Key length of 2048: Validity period = not greater than 2 years Key length of 4096: Validity period = not greater than 16 years
Edit :) ok, so let's try some more:
There is this recommendation from US government that says that shouldn't be longer than 3 years. And the validity period should be related to the interaction necessary to "renew" it: the more human interation is necessary, the longer the time, up to 3 years.
In Brazil, the recommendation is: source
1024 bits, software generated: 1 year if stored in software and 2 years if in hardware (token)
1024 bits, hardware generated: 3 years if stored in hardware
The expiration date for a certificate should be set to the date at which you would like the certificate owner to come back for a renewal. This is a matter of trade-offs:
There are various "estimates" for "key strength" depending on its length, and these sometimes come with recommendation of key lifetime. This kind of job if 10% science, 90% "educated guesswork", which is a kind of divination. See this site for a lot of data. In particular, NIST says that a 2048-bit RSA key ought to be fine until at least year 2030. But the difference between a "maybe crackable key" and a "maybe not crackable key" is very fuzzy, so don't expect hard data here.
In practice, key strength far exceeds actual certificate lifetimes. Typical lifetimes for end-entity certificates range from one to three years; make that five to ten years for intermediate CA. For a root CA, make it expire in 2037 (i.e. as far as possible in the future but without crossing the fateful Y2038 problem).