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I understand the reasons behind wanting to shorten certificate validity periods, but CA or root certificates often have expiration periods far into the future.

I understand the reasons behind wanting to shorten certificate validity periods, but CA or root certificates often have expiration periods far into the future. What’s the argument for this? Ease of use? Historical reasons?

jakub_g 7y ago
It's not easy to (at least this was the case until a few years ago) to ship updates to an old device (think Android 4.x or Windows XP; even worse for embedded systems). Hence to avoid the devices become useless bricks even if otherwise fully functional, root certs need to have more than a decade cert validity at minimum. (That's my personal theory, I'm not in the industry).
- userbinator 7y ago
  I think the industry is very much trying to push for the exact opposite of that, with things like planned obolescence to ensure you keep consuming their latest products.
gruez 7y ago
Because those certificates are much well guarded (HSMs), rather than an unencrypted .pem file sitting on a server or someone's computer.
dtech 7y ago
Root certificates are special. They are shipped to the device out-of-band, e.g. with OS updates. This makes them much more difficult to replace than other certificates, especially on devices that do not receive updates often like embedded devices and mobile phones. For this reason root certificates have a very long validity and very stringent requirements in their security parameters, e.g. large key sizes, and how they are used. Usually the certificate sits in a well secured off-network physical device and is only used a few times during its lifetime to sign sub-certificates.
jcranmer 7y ago
The two big reasons for short certificate validity periods are to manage revocation issues (expiry is the one guaranteed way to revoke a certificate), and to reduce the risk of forgetting to renew certificates (by having to rotate them more frequently, your IT is more likely to have better processes in place). There's a secondary concern of reducing the ability of CAs to backdate certificates (which happened when SHA-1 was prohibited). Neither of those really apply to the root certificate store. Updating the root certificate (to add or remove CAs) requires an OS/browser update instead of relying on CRL or OCSP queries which are flakier--and browsers have a variety of mechanisms to punish misbehaving CAs that aren't "drop you from the root store effective immediately." Meanwhile, the process for updating root stores is entirely different than regular certificates, and it takes months to years to add a new root certificate--and I believe you don't get a pass to merely update your new root certificate for an existing CA. The other risks with overly long validity times are ameliorated in large degree by the fact that CAs are regularly audited and have much greater scrutiny placed on their issuance.

jakub_g 7y ago

It's not easy to (at least this was the case until a few years ago) to ship updates to an old device (think Android 4.x or Windows XP; even worse for embedded systems). Hence to avoid the devices become useless bricks even if otherwise fully functional, root certs need to have more than a decade cert validity at minimum. (That's my personal theory, I'm not in the industry).

userbinator 7y ago
I think the industry is very much trying to push for the exact opposite of that, with things like planned obolescence to ensure you keep consuming their latest products.

gruez 7y ago

Because those certificates are much well guarded (HSMs), rather than an unencrypted .pem file sitting on a server or someone's computer.

dtech 7y ago

Root certificates are special. They are shipped to the device out-of-band, e.g. with OS updates. This makes them much more difficult to replace than other certificates, especially on devices that do not receive updates often like embedded devices and mobile phones. For this reason root certificates have a very long validity and very stringent requirements in their security parameters, e.g. large key sizes, and how they are used. Usually the certificate sits in a well secured off-network physical device and is only used a few times during its lifetime to sign sub-certificates.

jcranmer 7y ago

The two big reasons for short certificate validity periods are to manage revocation issues (expiry is the one guaranteed way to revoke a certificate), and to reduce the risk of forgetting to renew certificates (by having to rotate them more frequently, your IT is more likely to have better processes in place). There's a secondary concern of reducing the ability of CAs to backdate certificates (which happened when SHA-1 was prohibited). Neither of those really apply to the root certificate store. Updating the root certificate (to add or remove CAs) requires an OS/browser update instead of relying on CRL or OCSP queries which are flakier--and browsers have a variety of mechanisms to punish misbehaving CAs that aren't "drop you from the root store effective immediately." Meanwhile, the process for updating root stores is entirely different than regular certificates, and it takes months to years to add a new root certificate--and I believe you don't get a pass to merely update your new root certificate for an existing CA. The other risks with overly long validity times are ameliorated in large degree by the fact that CAs are regularly audited and have much greater scrutiny placed on their issuance.