openpgp: Do not reject signatures made prior to key expiration

If the key is expired, reject it only if the signature was made after
the key expired.  This only works in isolated environments where we
control key trust explicitly — as GnuPG will consider all expired keys
untrusted.

Signed-off-by: Michał Górny <mgorny@gentoo.org>

1 files changed, 34 insertions, 6 deletions

diff --git a/tests/test_openpgp.py b/tests/test_openpgp.py
index aa6d2d7..0c93839 100644
--- a/tests/test_openpgp.py
+++ b/tests/test_openpgp.py
@@ -106,6 +106,24 @@ mkkhTd2Auao4D2K74BePBuiZ9+eDQA==
 -----END PGP SIGNATURE-----
 """
 
+POST_EXPIRATION_SIGNED_MANIFEST = f"""
+-----BEGIN PGP SIGNED MESSAGE-----
+Hash: SHA256
+
+{COMMON_MANIFEST_TEXT}
+-----BEGIN PGP SIGNATURE-----
+
+iQEzBAEBCAAdFiEEgeEsFr2NzWC+GAhFE2iA5yp7E4QFAmPsj28ACgkQE2iA5yp7
+E4R0xAf8CC6uh8VMmv8xlFePEoBYEuSUtDa2hWHJv1sMn90QnszHGG6oo32g2Lje
+H9NRyjOltAG9t0siF/pf57EiKCs9B+Z9zLGYuWlK4gvkHjMHzsoTipUymm2/saEo
+AuoeZvhqNtfU0hCIJsWENtdyMb/hsJIxIOwBjVS/JT5cZlOGjhlyxVO0CS/7FsCp
+GZCeLYPdYXPw2em2DR3Q3NDuNmUY7W3WhJCL14uC+AkU64SnHc13xQ9/go6TQ2ho
+783Jm2f/4ZREYpKMvCgUJvOADSqnfY89hc6B/9JCXn+Zm8a31zgENlJ8DEhN0JMN
+le/JaXEH/AhO6xCOmk8tNQ3QXcNF5w==
+=UGgA
+-----END PGP SIGNATURE-----
+"""
+
 DASH_ESCAPED_SIGNED_MANIFEST = '''
 -----BEGIN PGP SIGNED MESSAGE-----
 Hash: SHA256
@@ -251,6 +269,7 @@ _ = VALID_KEY_SUBKEY
                           "MODIFIED_SIGNED_MANIFEST",
                           "EXPIRED_SIGNED_MANIFEST",
                           "TWO_SIGNATURE_MANIFEST",
+                          "POST_EXPIRATION_SIGNED_MANIFEST",
                           ])
 def test_noverify_goodish_manifest_load(manifest_var):
     """Test Manifest files that should succeed (OpenPGP disabled)"""
@@ -385,6 +404,9 @@ MANIFEST_VARIANTS = [
     ('SIGNED_MANIFEST', 'COMBINED_PUBLIC_KEYS', None),
     ('DASH_ESCAPED_SIGNED_MANIFEST', 'VALID_PUBLIC_KEY', None),
     ('SUBKEY_SIGNED_MANIFEST', 'VALID_KEY_SUBKEY', None),
+    ("POST_EXPIRATION_SIGNED_MANIFEST", "VALID_PUBLIC_KEY", None),
+    # == Manifest signed before the key expired ==
+    ("SIGNED_MANIFEST", "EXPIRED_PUBLIC_KEY", None),
     # == Manifest with two signatures ==
     ("TWO_SIGNATURE_MANIFEST", "TWO_SIGNATURE_PUBLIC_KEYS", None),
     ("TWO_SIGNATURE_MANIFEST", "VALID_PUBLIC_KEY", OpenPGPVerificationFailure),
@@ -402,7 +424,7 @@ MANIFEST_VARIANTS = [
     # == bad keys ==
     ('SIGNED_MANIFEST', None,
      OpenPGPVerificationFailure),
-    ('SIGNED_MANIFEST', 'EXPIRED_PUBLIC_KEY',
+    ("POST_EXPIRATION_SIGNED_MANIFEST", "EXPIRED_PUBLIC_KEY",
      OpenPGPExpiredKeyFailure),
     ('SIGNED_MANIFEST', 'REVOKED_PUBLIC_KEY',
      OpenPGPRevokedKeyFailure),
@@ -451,6 +473,12 @@ def assert_signature(sig: OpenPGPSignatureList,
         assert sig.timestamp == SUBKEY_SIG_TIMESTAMP
         assert sig.expire_timestamp is None
         assert sig.primary_key_fingerprint == KEY_FINGERPRINT
+    elif manifest_var == "POST_EXPIRATION_SIGNED_MANIFEST":
+        assert len(sig) == 1
+        assert sig.fingerprint == KEY_FINGERPRINT
+        assert sig.timestamp == datetime.datetime(2023, 2, 15, 7, 53, 19)
+        assert sig.expire_timestamp is None
+        assert sig.primary_key_fingerprint == KEY_FINGERPRINT
     else:
         assert len(sig) == 1
         assert sig.fingerprint == KEY_FINGERPRINT
@@ -482,7 +510,7 @@ def test_verify_manifest(openpgp_env, manifest_var, key_var, expected):
                         with io.BytesIO(globals()[key_var]) as kf:
                             openpgp_env.import_key(kf)
 
-                    openpgp_env.verify_file(f)
+                    print(openpgp_env.verify_file(f))
     except OpenPGPNoImplementation as e:
         pytest.skip(str(e))
 
@@ -825,16 +853,16 @@ REFRESH_VARIANTS = [
     ('SIGNED_MANIFEST', 'EXPIRED_PUBLIC_KEY', KEY_FINGERPRINT,
      'UNEXPIRE_PUBLIC_KEY', None),
     # ...but only with a new signature
-    ('SIGNED_MANIFEST', 'EXPIRED_PUBLIC_KEY', KEY_FINGERPRINT,
-     'OLD_UNEXPIRE_PUBLIC_KEY', OpenPGPExpiredKeyFailure),
+    ("POST_EXPIRATION_SIGNED_MANIFEST", "EXPIRED_PUBLIC_KEY", KEY_FINGERPRINT,
+     "OLD_UNEXPIRE_PUBLIC_KEY", OpenPGPExpiredKeyFailure),
     # make sure server can't malicously inject or replace key
     ('SIGNED_MANIFEST', 'OTHER_VALID_PUBLIC_KEY', OTHER_KEY_FINGERPRINT,
      'VALID_PUBLIC_KEY', OpenPGPKeyRefreshError),
     ('SIGNED_MANIFEST', 'OTHER_VALID_PUBLIC_KEY', OTHER_KEY_FINGERPRINT,
      'COMBINED_PUBLIC_KEYS', OpenPGPRuntimeError),
     # test that forged keys are rejected
-    ('SIGNED_MANIFEST', 'EXPIRED_PUBLIC_KEY', KEY_FINGERPRINT,
-     'FORGED_UNEXPIRE_KEY', OpenPGPExpiredKeyFailure),
+    ("POST_EXPIRATION_SIGNED_MANIFEST", "EXPIRED_PUBLIC_KEY", KEY_FINGERPRINT,
+     "FORGED_UNEXPIRE_KEY", OpenPGPExpiredKeyFailure),
     ('SUBKEY_SIGNED_MANIFEST', 'VALID_PUBLIC_KEY', KEY_FINGERPRINT,
      'FORGED_SUBKEY', OpenPGPVerificationFailure),
     ('SUBKEY_SIGNED_MANIFEST', 'VALID_PUBLIC_KEY', KEY_FINGERPRINT,