format3_signed is written by EncryptFiles with a test key. Its record gives
the seed of the key, control_commit, head_digest, signers_digest,
AUTHOR_MESSAGE with its code, the signature and the content of key 2, and
verdicts carries the dkauthor1 key. The conformance test recomputes all of
it from the control, the head and the security area, and signs again from
the seed. A second test changes the context, a bit of the signature or of
the key, and the key itself, and removes the signature.
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
