Questions about particular use cases (integrity verification w/o private key, add E flag to primary key, import secp256k1 key)

[Robert J. Hansen]

> Well, you can go one step further.  Unless the sender is throwing the
> key ids, you can look to see which keyids are given as hints in the
> outermost layer, to see which people are expected to be able to decrypt
> it.

Sure, but this is a heuristic, not a formal verification.  A useful
heuristic, absolutely, but this is still at the level of "let's look at
the packets to glean publicly available data" -- whereas message
sanitization and verification would require access to the content of the
message.

Part of this is, I think, the OP is being a little handwavy with the
idea of verification/sanitization.  If what you're checking is dependent
in any way on the cleartext, then you're screwed.  And if what you're
checking is dependent on the ciphertext, you're not really dealing with
the message at all, but the container it's packaged into.