[omemo] Refactor Plugin

- Adapt to nbxmpp supporting OMEMO
- Move python-axolotl code into backend folder

omemo/backend/aes.py

@@ -0,0 +1,86 @@
+# Copyright (C) 2019 Philipp Hörist <philipp AT hoerist.com>
+#
+# This file is part of OMEMO Gajim Plugin.
+#
+# OMEMO Gajim Plugin is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published
+# by the Free Software Foundation; version 3 only.
+#
+# OMEMO Gajim Plugin is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with OMEMO Gajim Plugin. If not, see <http://www.gnu.org/licenses/>.
+
+
+import os
+import logging
+from collections import namedtuple
+
+from cryptography.hazmat.primitives.ciphers import Cipher
+from cryptography.hazmat.primitives.ciphers import algorithms
+from cryptography.hazmat.primitives.ciphers.modes import GCM
+from cryptography.hazmat.backends import default_backend
+
+log = logging.getLogger('gajim.plugin_system.omemo')
+
+EncryptionResult = namedtuple('EncryptionResult', 'payload key iv')
+
+
+def _decrypt(key, iv, tag, data):
+    decryptor = Cipher(
+        algorithms.AES(key),
+        GCM(iv, tag=tag),
+        backend=default_backend()).decryptor()
+    return decryptor.update(data) + decryptor.finalize()
+
+
+def aes_decrypt(_key, iv, payload):
+    if len(_key) >= 32:
+        # XEP-0384
+        log.debug('XEP Compliant Key/Tag')
+        data = payload
+        key = _key[:16]
+        tag = _key[16:]
+    else:
+        # Legacy
+        log.debug('Legacy Key/Tag')
+        data = payload[:-16]
+        key = _key
+        tag = payload[-16:]
+
+    return _decrypt(key, iv, tag, data).decode()
+
+
+def aes_decrypt_file(key, iv, payload):
+    data = payload[:-16]
+    tag = payload[-16:]
+    return _decrypt(key, iv, tag, data)
+
+
+def _encrypt(data, key_size, iv_size):
+    if isinstance(data, str):
+        data = data.encode()
+    key = os.urandom(key_size)
+    iv = os.urandom(iv_size)
+    encryptor = Cipher(
+        algorithms.AES(key),
+        GCM(iv),
+        backend=default_backend()).encryptor()
+
+    payload = encryptor.update(data) + encryptor.finalize()
+    return key, iv, encryptor.tag, payload
+
+
+def aes_encrypt(plaintext):
+    key, iv, tag, payload = _encrypt(plaintext, 16, 16)
+    key += tag
+    return EncryptionResult(payload=payload, key=key, iv=iv)
+
+
+def aes_encrypt_file(data):
+    key, iv, tag, payload, = _encrypt(data, 32, 16)
+    payload += tag
+    return EncryptionResult(payload=payload, key=key, iv=iv)