prototype implementation for reading encrypted emails

pgp_mime_lib/reader.py

+# https://github.com/leapcode/leap_mail/blob/develop/src/leap/mail/incoming/service.py
+# should consider get_email_charset from:
+# https://github.com/leapcode/leap_pycommon/blob/6efdee0a5bab59d90c915b44a65e798b4a426c4a/src/leap/common/mail.py
+
+from email.utils import parseaddr
+
+
+MULTIPART_ENCRYPTED = "multipart/encrypted"
+MULTIPART_SIGNED = "multipart/signed"
+PGP_BEGIN = "-----BEGIN PGP MESSAGE-----"
+PGP_END = "-----END PGP MESSAGE-----"
+
+
+class ReaderException(Exception):
+    pass
+
+
+def extract_text_payload(msg):
+    if msg.is_multipart():
+        text = u''
+        for part in msg.walk():
+            if part.get_content_type() == 'text/plain':
+                text += unicode(part.get_payload(decode=True),
+                                part.get_content_charset('utf-8'))
+    else:
+        text = unicode(msg.get_payload(decode=True),
+                       msg.get_content_charset('utf-8'))
+    return text
+
+
+def decrypt_multipart(msg, sender_address, gpg):
+    payload = msg.get_payload()
+    if (len(payload) != 2 or
+            payload[0].get_content_type() != 'application/pgp-encrypted' or
+            payload[1].get_content_type() != 'application/octet-stream'):
+        raise ReaderException("Invalid format for a multipart encrypted message")
+    enc_data = payload[1].get_payload()
+    data = str(gpg.decrypt(enc_data))
+
+    return data
+
+
+def maybe_decrypt_inline(msg, sender_address, gpg):
+    """Decrypt a inline PGP message or a normal plain text message"""
+
+    data = extract_text_payload(msg)
+    was_encrypted = False
+
+    if PGP_BEGIN in data and PGP_END in data:
+        begin = data.find(PGP_BEGIN)
+        end = data.find(PGP_END)
+        if begin > end:
+            raise ReaderException("Invalid inline PGP message")
+        pgp_message = data[begin:end + len(PGP_END)]
+        if len(pgp_message) == 0:
+            raise ReaderException("Empty inline PGP message")
+        was_encrypted = True
+        return (str(gpg.decrypt(pgp_message)), was_encrypted)
+
+    return (data, was_encrypted)
+
+
+def read_encrypted_message(msg, gpg):
+    """Return the body of a email message, wether it is encrypted or not."""
+
+    was_encrypted = False
+    content_type = msg.get_content_type()
+
+    from_header = msg.get('from', None)
+    sender_address = None
+    if from_header is not None and content_type in (MULTIPART_ENCRYPTED,
+                                                    MULTIPART_SIGNED):
+        sender_address = parseaddr(from_header)[1]
+
+    if content_type == MULTIPART_ENCRYPTED:
+        was_encrypted = True
+        data = decrypt_multipart(msg, sender_address, gpg)
+    elif content_type == MULTIPART_SIGNED:
+        raise ReaderException("Signed but not encrypted messages are not supported yet")
+    else:
+        (data, was_encrypted) = maybe_decrypt_inline(msg, sender_address, gpg)
+
+    return (data, was_encrypted)

[sand]

@ale ☝ potrebbe essere un punto di partenza...