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there is a difference between the expiration of signing keys, and the expiration of the signature signed with those keys. the signature for a contract, or a bootloader, should remain valid indefinitely, even if the person/key is no longer allowed to sign contracts/bootloaders after some point of time.

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That sounds impossible to enforce. Key signing is done offline. If I have an expired signing key, what’s stopping me setting my clock back a few years, creating a new signature and signing it?

If the resulting key works indefinitely, the expiration date on my signing key is utterly meaningless.

And what stops people from just logging into the bios and changing the date or pulling the clock battery? The point we're all making here is, at least for this application, is that an expiration is pointless.

Trusted timestamp services. https://en.wikipedia.org/wiki/Trusted_timestamping

Microsoft's Authenticode has been doing this for a long time, allowing a signature to be considered as valid long after the signing certificate expired.

https://learn.microsoft.com/en-us/windows/win32/seccrypto/ti...

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