diff --git a/changelog.d/6803.misc b/changelog.d/6803.misc
new file mode 100644
index 000000000000..08aa80bcd91f
--- /dev/null
+++ b/changelog.d/6803.misc
@@ -0,0 +1 @@
+Refactoring work in preparation for changing the event redaction algorithm.
diff --git a/synapse/events/__init__.py b/synapse/events/__init__.py
index 72c09327f43a..f813fa2fe7cb 100644
--- a/synapse/events/__init__.py
+++ b/synapse/events/__init__.py
@@ -23,6 +23,7 @@
 
 from synapse.api.errors import UnsupportedRoomVersionError
 from synapse.api.room_versions import KNOWN_ROOM_VERSIONS, EventFormatVersions
+from synapse.types import JsonDict
 from synapse.util.caches import intern_dict
 from synapse.util.frozenutils import freeze
 
@@ -197,7 +198,7 @@ def membership(self):
     def is_state(self):
         return hasattr(self, "state_key") and self.state_key is not None
 
-    def get_dict(self):
+    def get_dict(self) -> JsonDict:
         d = dict(self._event_dict)
         d.update({"signatures": self.signatures, "unsigned": dict(self.unsigned)})
 
@@ -209,7 +210,7 @@ def get(self, key, default=None):
     def get_internal_metadata_dict(self):
         return self.internal_metadata.get_dict()
 
-    def get_pdu_json(self, time_now=None):
+    def get_pdu_json(self, time_now=None) -> JsonDict:
         pdu_json = self.get_dict()
 
         if time_now is not None and "age_ts" in pdu_json["unsigned"]:
diff --git a/synapse/python_dependencies.py b/synapse/python_dependencies.py
index 5871feaafdf9..8de8cb2c1287 100644
--- a/synapse/python_dependencies.py
+++ b/synapse/python_dependencies.py
@@ -1,6 +1,7 @@
 # Copyright 2015, 2016 OpenMarket Ltd
 # Copyright 2017 Vector Creations Ltd
 # Copyright 2018 New Vector Ltd
+# Copyright 2020 The Matrix.org Foundation C.I.C.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -43,7 +44,8 @@
     "frozendict>=1",
     "unpaddedbase64>=1.1.0",
     "canonicaljson>=1.1.3",
-    "signedjson>=1.0.0",
+    # we use the type definitions added in signedjson 1.1.
+    "signedjson>=1.1.0",
     "pynacl>=1.2.1",
     "idna>=2.5",
     # validating SSL certs for IP addresses requires service_identity 18.1.
diff --git a/synapse/types.py b/synapse/types.py
index 65e4d8c18167..f3cd465735fd 100644
--- a/synapse/types.py
+++ b/synapse/types.py
@@ -17,7 +17,7 @@
 import string
 import sys
 from collections import namedtuple
-from typing import Dict, Tuple, TypeVar
+from typing import Any, Dict, Tuple, TypeVar
 
 import attr
 from signedjson.key import decode_verify_key_bytes
@@ -43,6 +43,11 @@ class Collection(Iterable[T_co], Container[T_co], Sized):
 StateMap = Dict[Tuple[str, str], T]
 
 
+# the type of a JSON-serialisable dict. This could be made stronger, but it will
+# do for now.
+JsonDict = Dict[str, Any]
+
+
 class Requester(
     namedtuple(
         "Requester", ["user", "access_token_id", "is_guest", "device_id", "app_service"]
diff --git a/tests/storage/test_keys.py b/tests/storage/test_keys.py
index e07ff0120173..95f309fbbc41 100644
--- a/tests/storage/test_keys.py
+++ b/tests/storage/test_keys.py
@@ -14,6 +14,7 @@
 # limitations under the License.
 
 import signedjson.key
+import unpaddedbase64
 
 from twisted.internet.defer import Deferred
 
@@ -21,11 +22,17 @@
 
 import tests.unittest
 
-KEY_1 = signedjson.key.decode_verify_key_base64(
-    "ed25519", "key1", "fP5l4JzpZPq/zdbBg5xx6lQGAAOM9/3w94cqiJ5jPrw"
+
+def decode_verify_key_base64(key_id: str, key_base64: str):
+    key_bytes = unpaddedbase64.decode_base64(key_base64)
+    return signedjson.key.decode_verify_key_bytes(key_id, key_bytes)
+
+
+KEY_1 = decode_verify_key_base64(
+    "ed25519:key1", "fP5l4JzpZPq/zdbBg5xx6lQGAAOM9/3w94cqiJ5jPrw"
 )
-KEY_2 = signedjson.key.decode_verify_key_base64(
-    "ed25519", "key2", "Noi6WqcDj0QmPxCNQqgezwTlBKrfqehY1u2FyWP9uYw"
+KEY_2 = decode_verify_key_base64(
+    "ed25519:key2", "Noi6WqcDj0QmPxCNQqgezwTlBKrfqehY1u2FyWP9uYw"
 )