[Rpm-maint] [rpm-software-management/rpm] Installation / verification should not pass if the (sub)key(s) has been revoked or expired (#1598)

[Zoltan Kelemen]

I agree with @ffesti about key revokation being more complex than what it seems like. When you revoke, you don't want to invalidate the signatures created _before_ the revokation. That would require every existing package to be re-signed with the new key, which would be very disruptive.

But how can you trust the signature date? An attacker could create a new signature with a forged date. Therefore you need to add support for trusted third-party timestamping to the signatures. Unless I am mistaken, there is no such support in GPG:
https://dev.gnupg.org/T4108
https://dev.gnupg.org/T4537

The problem is not specific to RPM and package signatures. Git signatures, for example, also have the same issue:
https://petertodd.org/2016/opentimestamps-git-integration

Short term, the simplest way to deal with a compromised key, is to remove it from the RPM DB, just as @ffesti suggested. There should be a tested and planned process for how to do this, for example by sending an emergency update, perhaps signed with the disaster recovery key (in Red Hat case). It would also require all packages are re-signed with a new key, since the old ones will be invalidated after the key removal.

Long term, adding support for trusted timestamps would make key revokation much easier.

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