1 files changed, 74 insertions, 3 deletions

diff --git a/src/mailman_pgp/pgp/mime_multisig.py b/src/mailman_pgp/pgp/mime_multisig.py
index ff9039e..ced90fa 100644
--- a/src/mailman_pgp/pgp/mime_multisig.py
+++ b/src/mailman_pgp/pgp/mime_multisig.py
@@ -21,24 +21,62 @@ from email import message_from_string
 from email.encoders import encode_7or8bit
 from email.mime.application import MIMEApplication
 from email.mime.multipart import MIMEMultipart
+from email.utils import collapse_rfc2231_value
 
 from mailman.email.message import MultipartDigestMessage, Message
+from pgpy import PGPSignature, PGPDetachedSignature
 
 from mailman_pgp.pgp.mime import MIMEWrapper
 from mailman_pgp.utils.email import copy_headers
 
 
 class MIMEMultiSigWrapper(MIMEWrapper):
-    """"""
+    """https://tools.ietf.org/html/draft-ietf-openpgp-multsig-02"""
+
     _signature_preamble = \
         'This is an OpepPGP/MIME signed message' \
         '(RFC 4880, 3156 and draft-ietf-openpgp-multsig).\n' \
         'see https://tools.ietf.org/html/draft-ietf-openpgp-multsig-02' \
         'for more details.'
 
+    def is_signed(self):
+        """
+        Whether the whole message is MIME signed as per draft-ietf-openpgp-multsig-02.
+
+        :return: If the message is MIME signed.
+        :rtype: bool
+        """
+        if not self._is_mime():
+            return False
+        second_part = self.msg.get_payload(1)
+        second_type = second_part.get_content_type()
+        protocol_param = collapse_rfc2231_value(self.msg.get_param('protocol',
+                                                                   ''))
+        content_subtype = self.msg.get_content_subtype()
+
+        return (second_part.is_multipart() and
+                second_type == 'multipart/mixed' and
+                content_subtype == 'signed' and
+                protocol_param == 'multipart/mixed' and
+                all(part.get_content_type() == MIMEWrapper._signed_type
+                    for part in second_part.get_payload()))
+
+    def get_signature(self):
+        """
+
+        :return:
+        :rtype: typing.Generator[pgpy.PGPSignature]
+        """
+        for part in self.msg.get_payload(1).get_payload():
+            try:
+                sig = PGPSignature.from_blob(part.get_payload())
+            except:
+                continue
+            yield sig
+
     def _wrap_signed_multiple(self, msg, signature):
         """
-        As per https://tools.ietf.org/html/draft-ietf-openpgp-multsig-02.
+        As per draft-ietf-openpgp-multsig-02.
 
         :param msg:
         :param signature:
@@ -67,15 +105,48 @@ class MIMEMultiSigWrapper(MIMEWrapper):
         return out
 
     def sign(self, key, hash=None):
+        """
+        Sign a message with key.
+
+        :param key: The key to sign with.
+        :type key: pgpy.PGPKey
+        :param hash:
+        :type hash: pgpy.constants.HashAlgorithm
+        :return: The signed message.
+        :rtype: mailman.email.message.Message
+        """
         if self.is_signed():
             payload = next(iter(self.get_signed()))
-            signature = next(iter(self.get_signature()))
+            signature = PGPDetachedSignature()
+            for sig in self.get_signature():
+                signature |= sig
             signature |= key.sign(payload, hash=hash)
             return self._wrap_signed_multiple(self.msg, signature)
         else:
             super().sign(key, hash)
 
+    def verify(self, key):
+        """
+        Verify the signature of this message with key.
+
+        :param key: The key to verify with.
+        :type key: pgpy.PGPKey
+        :return: The verified signature.
+        :rtype: Generator[pgpy.types.SignatureVerification]
+        """
+        clear_text = next(iter(self.get_signed()))
+        for signature in self.get_signature():
+            yield key.verify(clear_text, signature)
+
     def decrypt(self, key):
+        """
+        Decrypt this message with key.
+
+        :param key: The key to decrypt with.
+        :type key: pgpy.PGPKey
+        :return: The decrypted message.
+        :rtype: mailman.email.message.Message
+        """
         pmsg = next(iter(self.get_encrypted()))
         decrypted = key.decrypt(pmsg)