2 files changed, 40 insertions, 3 deletions

diff --git a/src/mailman_pgp/pgp/mime.py b/src/mailman_pgp/pgp/mime.py
index f3b0d32..08bd111 100644
--- a/src/mailman_pgp/pgp/mime.py
+++ b/src/mailman_pgp/pgp/mime.py
@@ -1 +1,37 @@
 """"""
+from email.message import Message
+from email.utils import collapse_rfc2231_value
+
+
+class PGPMIMEWrapper:
+    def __init__(self, msg: Message):
+        self.msg = msg
+
+    def _is_mime(self):
+        is_multipart = self.msg.is_multipart()
+        payloads = len(self.msg.get_payload())
+        first_part = self.msg.get_payload(0)
+        return is_multipart and payloads == 2 and 'Version: 1' in first_part
+
+    def is_mime_signed(self):
+        """
+        Whether the whole message is MIME signed as per RFC3156 section 5.
+        :return:
+        """
+        protocol_param = collapse_rfc2231_value(self.msg.get_param('protocol'))
+        content_subtype = self.msg.get_content_subtype()
+        return self._is_mime() and \
+               content_subtype == 'signed' and \
+               protocol_param == 'application/pgp-signature'
+
+    def is_mime_encrypted(self):
+        """
+        Whether the whole message is MIME encrypted as per RFC3156 section 4.
+        :return:
+        """
+        content_subtype = self.msg.get_content_subtype()
+        protocol_param = collapse_rfc2231_value(self.msg.get_param('protocol'))
+
+        return self._is_mime() and \
+               content_subtype == 'encrypted' and \
+               protocol_param == 'application/pgp-encrypted'
diff --git a/src/mailman_pgp/runners/incoming.py b/src/mailman_pgp/runners/incoming.py
index ddc08aa..3c69a23 100644
--- a/src/mailman_pgp/runners/incoming.py
+++ b/src/mailman_pgp/runners/incoming.py
@@ -1,6 +1,5 @@
 """The encryption-aware incoming runner."""
 
-from gpgmime import is_encrypted, is_signed
 from mailman.config import config as mailman_config
 from mailman.core.runner import Runner
 from mailman.email.message import Message
@@ -9,6 +8,7 @@ from public import public
 
 from mailman_pgp.config import config
 from mailman_pgp.model.list import EncryptedMailingList
+from mailman_pgp.pgp.mime import PGPMIMEWrapper
 
 
 @public
@@ -25,10 +25,11 @@ class IncomingRunner(Runner):
                                                      listid=mlist.list_id)
             return False
         # Is the message encrypted?
-        if is_signed(msg):
+        mime = PGPMIMEWrapper(msg)
+        if mime.is_mime_signed():
             # only signed.
             pass
-        elif is_encrypted(msg):
+        elif mime.is_mime_encrypted():
             # definitely encrypted, might still be signed
             pass
         else: