Merge pull request #394 from ignaloidas/default-to-3DES

Default to 3DES when preferred algorithms don't have any supporting algorithm

pgpy/pgp.py

@@ -2437,7 +2437,7 @@ class PGPKey(Armorable, ParentRef, PGPObject):
             uid = next(iter(self.userids), None)
             if uid is None and self.parent is not None:
                 uid = next(iter(self.parent.userids), None)
-        pref_cipher = next(c for c in uid.selfsig.cipherprefs if c.is_supported)
+        pref_cipher = next((c for c in uid.selfsig.cipherprefs if c.is_supported), SymmetricKeyAlgorithm.TripleDES)
         cipher_algo = prefs.pop('cipher', pref_cipher)
 
         if cipher_algo not in uid.selfsig.cipherprefs:

tests/test_99_regressions.py

@@ -583,3 +583,25 @@ cjMX82ahGPUVlyMP4A==
     key = PGPKey.from_file('tests/testdata/keys/rsa.1.pub.asc')[0]
     message = PGPMessage.from_blob(message_data)
     assert key.verify(message)
+
+@pytest.mark.regression(issue=393)
+def test_preference_no_supported_ciphers():
+    from pgpy import PGPMessage
+    keyblob = '''-----BEGIN PGP PUBLIC KEY BLOCK-----
+
+xo0EYmAayAEEAPQ0oYaLBPIF7bOA71X6kI0j7xnevfaHWfRzCoOJcDH4WJIRDbXD
+cUkcKJoc710mRZREQm6HYcd61DBsohW3HT96h0/1HE4E1SbgN1GIAjh9rFiNy9F4
+/M5LHtn+KzsG1yB4eTOyOw5nr+y6DEVaw0a3dnTC541x1LnMplU0HAW3ABEBAAHN
+G3Rlc3Qga2V5IDx0ZXN0QGV4YW1wbGUuY29tPsK8BBMBAgAmBQJiYBrLAhsvAhUC
+Ah4BFiEErFJI/ShgHoPluKoDdK7/b7+9sGcACgkQdK7/b7+9sGcNlgP8D8hL8g3e
+wP0HNxs7lXHyWT/uv6d02qEu/ZZ0fqf3CbEJ0aJQqDL61/utWK9hOt6nwTh+YvQP
+VSigo9gDqyHdbq8fvKxeiKJIkCZmESN0RpSjf+JQrBLs9DSOWh4bLQ9EiE6GfgdL
+n1hJ4Wx1aFL7WuPz/wj69MxPLh3nrG6i4iw=
+=aDo/
+-----END PGP PUBLIC KEY BLOCK-----'''
+
+    pubkey, _ = PGPKey.from_blob(keyblob)
+    msg = PGPMessage.new('asdf')
+    with warnings.catch_warnings():
+        warnings.simplefilter('ignore')
+        pubkey.encrypt(msg)