Add gpg.export_pubkeys function

Add convenience function to export multiple public keys from a
gpg keyring into an sslib dict format at once and tests.

Note: Uses the new pseudo-standard docstring style suggested in
secure-systems-lab/code-style-guidelines#20. All new interface
functions should use that style (existing docstrings will be
converted in separate PRs).

securesystemslib/gpg/functions.py

@@ -299,3 +299,29 @@ def export_pubkey(keyid, homedir=None):
   key_bundle = securesystemslib.gpg.common.get_pubkey_bundle(key_packet, keyid)
 
   return key_bundle
+
+
+def export_pubkeys(keyids, homedir=None):
+  """Export multiple public keys from a GnuPG keyring.
+
+  Arguments:
+    keyid: A list of OpenPGP keyids in KEYID_SCHEMA format.
+    homedir (optional): A path to the GnuPG home directory. If not set the
+        default GnuPG home directory is used.
+
+  Raises:
+    TypeError: Keyids is not iterable.
+    See 'export_pubkey' for other exceptions.
+
+  Returns:
+    A dict with OpenPGP keyids for dict keys and keys in GPG_PUBKEY_SCHEMA
+    format for values.
+
+  """
+  public_key_dict = {}
+  for gpg_keyid in keyids:
+    public_key = export_pubkey(gpg_keyid, homedir=homedir)
+    keyid = public_key["keyid"]
+    public_key_dict[keyid] = public_key
+
+  return public_key_dict

tests/check_public_interfaces_gpg.py

@@ -48,6 +48,10 @@ def test_gpg_functions(self):
       export_pubkey('f00')
     self.assertEqual(NO_GPG_MSG, str(ctx.exception))
 
+    with self.assertRaises(UnsupportedLibraryError) as ctx:
+      export_pubkeys(['f00'])
+    self.assertEqual(NO_GPG_MSG, str(ctx.exception))
+
     with self.assertRaises(UnsupportedLibraryError) as ctx:
       get_version()
     self.assertEqual(NO_GPG_MSG, str(ctx.exception))

tests/test_gpg.py

@@ -40,7 +40,7 @@
 
 from securesystemslib import process
 from securesystemslib.gpg.functions import (create_signature, export_pubkey,
-    verify_signature)
+    verify_signature, export_pubkeys)
 from securesystemslib.gpg.util import (get_version, is_version_fully_supported,
     get_hashing_class, parse_packet_header, parse_subpacket_header)
 from securesystemslib.gpg.rsa import create_pubkey as rsa_create_pubkey
@@ -55,7 +55,8 @@
 from securesystemslib.gpg.exceptions import (PacketParsingError,
     PacketVersionNotSupportedError, SignatureAlgorithmNotSupportedError,
     KeyNotFoundError, CommandError, KeyExpirationError)
-from securesystemslib.formats import GPG_PUBKEY_SCHEMA
+from securesystemslib.formats import (GPG_PUBKEY_SCHEMA,
+    ANY_PUBKEY_DICT_SCHEMA)
 
 
 @unittest.skipIf(not HAVE_GPG, "gpg not found")
@@ -481,6 +482,8 @@ class TestGPGRSA(unittest.TestCase):
   unsupported_subkey_keyid = "611A9B648E16F54E8A7FAD5DA51E8CDF3B06524F"
   expired_key_keyid = "E8AC80C924116DABB51D4B987CB07D6D2C199C7C"
 
+  keyid_768C43 = "7B3ABB26B97B655AB9296BD15B0BD02E1C768C43"
+
   @classmethod
   def setUpClass(self):
     # Create directory to run the tests without having everything blow up
@@ -547,6 +550,17 @@ def test_export_pubkey(self):
     self.assertDictEqual(key_data, key_data2)
 
 
+  def test_export_pubkeys(self):
+    """Test export multiple pubkeys at once. """
+    key_dict = export_pubkeys([self.default_keyid, self.keyid_768C43],
+        homedir=self.gnupg_home)
+
+    ANY_PUBKEY_DICT_SCHEMA.check_match(key_dict)
+    self.assertListEqual(
+        sorted([self.default_keyid.lower(), self.keyid_768C43.lower()]),
+        sorted(key_dict.keys()))
+
+
   def test_gpg_sign_and_verify_object_with_default_key(self):
     """Create a signature using the default key on the keyring """