diff --git a/plugin.py b/plugin.py
index 510dfcb..5a13190 100644
--- a/plugin.py
+++ b/plugin.py
@@ -12,7 +12,6 @@ from typing import List, Union
 
 import os
 import json
-import time
 import base64
 import asyncio
 from slixmpp.plugins.xep_0384.stanza import OMEMO_BASE_NS
@@ -20,6 +19,7 @@ from slixmpp.plugins.xep_0384.stanza import OMEMO_DEVICES_NS, OMEMO_BUNDLES_NS
 from slixmpp.plugins.xep_0384.stanza import Devices, Device, Key, PreKeyPublic
 from slixmpp.plugins.base import BasePlugin, register_plugin
 from slixmpp.exceptions import IqError
+from slixmpp.stanza import Message, Iq
 
 log = logging.getLogger(__name__)
 
@@ -30,7 +30,7 @@ try:
     from omemo_backend_signal import BACKEND as SignalBackend
     from slixmpp.plugins.xep_0384.storage import SyncFileStorage
     from slixmpp.plugins.xep_0384.otpkpolicy import KeepingOTPKPolicy
-except ImportError as e:
+except (ImportError,):
     HAS_OMEMO = False
 
 TRUE_VALUES = {True, 'true', '1'}
@@ -41,14 +41,30 @@ TRUE_VALUES = {True, 'true', '1'}
 def encode_public_key(key: bytes) -> bytes:
     return b'\x05' + key
 
-def b64enc(data):
+
+def b64enc(data: bytes) -> str:
     return base64.b64encode(bytes(bytearray(data))).decode('ASCII')
 
 
-def b64dec(data):
+def b64dec(data: str) -> bytes:
     return base64.b64decode(data)
 
 
+def _load_device_id(cache_dir: str) -> int:
+    filepath = os.path.join(cache_dir, 'device_id.json')
+    # Try reading file first, decoding, and if file was empty generate
+    # new DeviceID
+    try:
+        with open(filepath, 'r') as f:
+            did = json.load(f)
+    except (FileNotFoundError, json.JSONDecodeError):
+        did = generateDeviceID()
+        with open(filepath, 'w') as f:
+            json.dump(did, f)
+
+    return did
+
+
 # XXX: This should probably be moved in plugins/base.py?
 class PluginCouldNotLoad(Exception): pass
 
@@ -68,19 +84,17 @@ class XEP_0384(BasePlugin):
 
     backend_loaded = HAS_OMEMO
 
-    device_ids = {}
-
     def plugin_init(self):
         if not self.backend_loaded:
             log.info("xep_0384 cannot be loaded as the backend omemo library "
-                      "is not available")
+                     "is not available")
             return
 
         storage = SyncFileStorage(self.cache_dir)
         otpkpolicy = KeepingOTPKPolicy()
         backend = SignalBackend
         bare_jid = self.xmpp.boundjid.bare
-        self._device_id = self._load_device_id(self.cache_dir)
+        self._device_id = _load_device_id(self.cache_dir)
 
         try:
             self._omemo = SessionManager.create(
@@ -105,27 +119,13 @@ class XEP_0384(BasePlugin):
         self.xmpp.del_event_handler('pubsub_publish', self._receive_device_list)
         self.xmpp['xep_0163'].remove_interest(OMEMO_DEVICES_NS)
 
-    def _load_device_id(self, cache_dir):
-        filepath = os.path.join(cache_dir, 'device_id.json')
-        # Try reading file first, decoding, and if file was empty generate
-        # new DeviceID
-        try:
-            with open(filepath, 'r') as f:
-                did = json.load(f)
-        except (FileNotFoundError, json.JSONDecodeError):
-            did = generateDeviceID()
-            with open(filepath, 'w') as f:
-                json.dump(did, f)
-
-        return did
-
     def session_bind(self, _jid):
         self.xmpp['xep_0163'].add_interest(OMEMO_DEVICES_NS)
 
-    def my_device_id(self):
+    def my_device_id(self) -> int:
         return self._device_id
 
-    def _generate_bundle_iq(self):
+    def _generate_bundle_iq(self) -> Iq:
         bundle = self._omemo.public_bundle
 
         iq = self.xmpp.Iq(stype='set')
@@ -151,13 +151,13 @@ class XEP_0384(BasePlugin):
 
         return iq
 
-    async def _publish_bundle(self):
+    async def _publish_bundle(self) -> None:
         if self._omemo.republish_bundle:
             iq = self._generate_bundle_iq()
             await iq.send()
 
-    def _store_device_ids(self, jid, items):
-        device_ids = []
+    def _store_device_ids(self, jid: str, items) -> None:
+        device_ids = []  # type: List[int]
         for item in items:
             device_ids = [int(d['id']) for d in item['devices']]
 
@@ -166,7 +166,7 @@ class XEP_0384(BasePlugin):
             break
         return self._omemo.newDeviceList(device_ids, str(jid))
 
-    def _receive_device_list(self, msg):
+    def _receive_device_list(self, msg: Message) -> None:
         if msg['pubsub_event']['items']['node'] != OMEMO_DEVICES_NS:
             return
 
@@ -181,7 +181,7 @@ class XEP_0384(BasePlugin):
            self._device_id not in active_devices:
             asyncio.ensure_future(self._set_device_list())
 
-    async def _set_device_list(self):
+    async def _set_device_list(self) -> None:
         jid = self.xmpp.boundjid.bare
 
         try:
@@ -216,14 +216,14 @@ class XEP_0384(BasePlugin):
             jid, OMEMO_DEVICES_NS, payload=payload,
         )
 
-    def get_device_list(self, jid) -> List[str]:
+    def get_device_list(self, jid: str) -> List[str]:
         # XXX: Maybe someday worry about inactive devices somehow
         return  self._omemo.getDevices(jid)
 
-    def is_encrypted(self, msg):
+    def is_encrypted(self, msg: Message) -> bool:
         return msg.xml.find('{%s}encrypted' % OMEMO_BASE_NS) is not None
 
-    def decrypt_message(self, msg) -> Union[None, str]:
+    def decrypt_message(self, msg: Message) -> Union[None, str]:
         header = msg['omemo_encrypted']['header']
         payload = b64dec(msg['omemo_encrypted']['payload']['value'])