verifier: Ensure that bundle digest and real digest match

[jku]

We verify that the signature is over the actual artifact digest but we did not verify that the actual digest matches the digest documented in the bundle.

Ensure that the digests match during verify.

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Fixes #1651

[woodruffw]

Thanks @jku, makes sense to me!

This is ancient history at this point, but I remember this being one of the reasons why I didn't want the hash in the bundle at all 😅 -- in this case it's a no-op field that adds extra cross-checking work, and in the worst case it's misleading (since users might think it does do something other than serve as an unauthenticated content hint).

I'd love it if a future bundle version removed it entirely, but it also seems like a pretty low priority thing to address.

[woodruffw]

(We should have a CHANGELOG entry for this too, in the unlikely event this snares someone. But if you prefer to do those at release time, I'll stop bugging on each PR about them.)

[jku]

This is ancient history at this point, but I remember this being one of the reasons why I didn't want the hash in the bundle at all 😅 -- in this case it's a no-op field that adds extra cross-checking work, and in the worst case it's misleading (since users might think it does do something other than serve as an unauthenticated content hint).

Yeah, I 100% agree. But now that it is in there, we should not accept a bundle with inconsistent info for exactly the reason in your parenthesis.

(We should have a CHANGELOG entry for this too, in the unlikely event this snares someone. But if you prefer to do those at release time, I'll stop bugging on each PR about them.)

I don't really have an opinion, I just keep forgetting. I'll add it here.