* guix/openpgp.scm (string->openpgp-packet): New procedure.
* tests/openpgp.scm ("verify-openpgp-signature, missing key")
("verify-openpgp-signature, good signatures")
("verify-openpgp-signature, bad signature"): Use it.
Previously, 'lookup-key-by-{id,fingerprint}' would always return the
list of packets where the primary key is first. Thus, the caller would
need to use 'find' to actually find the requested key.
* guix/openpgp.scm (keyring-insert): Always add KEY to PACKETS.
(lookup-key-by-id, lookup-key-by-fingerprint): Change to return the key
as the first value.
(verify-openpgp-signature): Remove now unneeded call to 'find'.
* tests/openpgp.scm ("get-openpgp-keyring"): Adjust accordingly.
* guix/openpgp.scm (verify-openpgp-signature): Use
'lookup-key-by-fingerprint' when SIG contains a fingerprint.
Honor FINGERPRINT in the 'find' predicate. Upon missing-key, return
FINGERPRINT if available.
* tests/openpgp.scm ("verify-openpgp-signature, missing key"): Adjust
expected value accordingly.
* guix/openpgp.scm (SUBPACKET-ISSUER-FINGERPRINT): New variable.
(openpgp-signature-issuer-fingerprint): New procedure.
(key-id-matches-fingerprint?): New procedure.
(get-signature): Look for the 'issuer and 'issuer-fingerprint
subpackets. Ensure the issuer key ID matches the fingerprint when both
are available.
(parse-subpackets): Handle SUBPACKET-ISSUER-FINGERPRINT.
* tests/openpgp.scm (%rsa-key-fingerprint)
(%dsa-key-fingerprint, %ed25519-key-fingerprint): New variables.
* tests/openpgp.scm ("get-openpgp-detached-signature/ascii"): Check the
result of 'openpgp-signature-issuer-fingerprint'.
