diff --git a/synapse/api/events/__init__.py b/synapse/api/events/__init__.py
index 1d8bed290..63c0bd7ae 100644
--- a/synapse/api/events/__init__.py
+++ b/synapse/api/events/__init__.py
@@ -117,6 +117,12 @@ class SynapseEvent(JsonEncodedObject):
         """
         raise NotImplementedError("get_content_template not implemented.")
 
+    def get_pdu_json(self):
+        pdu_json = self.get_full_dict()
+        pdu_json.pop("destination", None)
+        pdu_json.pop("outlier", None)
+        return pdu_json
+
 
 class SynapseStateEvent(SynapseEvent):
 
diff --git a/synapse/api/events/utils.py b/synapse/api/events/utils.py
index 802648f8f..d6019d56e 100644
--- a/synapse/api/events/utils.py
+++ b/synapse/api/events/utils.py
@@ -42,6 +42,8 @@ def prune_event(event):
         "prev_events",
         "prev_state",
         "auth_events",
+        "origin",
+        "origin_server_ts",
     ]
 
     new_content = {}
diff --git a/synapse/crypto/event_signing.py b/synapse/crypto/event_signing.py
index 79274fd55..4dff2c0ec 100644
--- a/synapse/crypto/event_signing.py
+++ b/synapse/crypto/event_signing.py
@@ -16,7 +16,6 @@
 
 
 from synapse.api.events.utils import prune_event
-from synapse.federation.units import Pdu
 from syutil.jsonutil import encode_canonical_json
 from syutil.base64util import encode_base64, decode_base64
 from syutil.crypto.jsonsign import sign_json
@@ -53,8 +52,7 @@ def check_event_content_hash(event, hash_algorithm=hashlib.sha256):
 
 
 def _compute_content_hash(event, hash_algorithm):
-    event_json = event.get_full_dict()
-    # TODO: We need to sign the JSON that is going out via fedaration.
+    event_json = event.get_pdu_json()
     event_json.pop("age_ts", None)
     event_json.pop("unsigned", None)
     event_json.pop("signatures", None)
@@ -67,7 +65,7 @@ def _compute_content_hash(event, hash_algorithm):
 
 def compute_event_reference_hash(event, hash_algorithm=hashlib.sha256):
     tmp_event = prune_event(event)
-    event_json = tmp_event.get_dict()
+    event_json = tmp_event.get_pdu_json()
     event_json.pop("signatures", None)
     event_json.pop("age_ts", None)
     event_json.pop("unsigned", None)
@@ -78,14 +76,7 @@ def compute_event_reference_hash(event, hash_algorithm=hashlib.sha256):
 
 def compute_event_signature(event, signature_name, signing_key):
     tmp_event = prune_event(event)
-    tmp_event.origin = event.origin
-    tmp_event.origin_server_ts = event.origin_server_ts
-    d = tmp_event.get_full_dict()
-    kwargs = dict(event.unrecognized_keys)
-    kwargs.update({k: v for k, v in d.items()})
-    tmp_pdu = Pdu(**kwargs)
-    redact_json = tmp_pdu.get_dict()
-    redact_json.pop("signatures", None)
+    redact_json = tmp_event.get_pdu_json()
     redact_json.pop("age_ts", None)
     redact_json.pop("unsigned", None)
     logger.debug("Signing event: %s", redact_json)
diff --git a/synapse/federation/pdu_codec.py b/synapse/federation/pdu_codec.py
deleted file mode 100644
index 52c84efb5..000000000
--- a/synapse/federation/pdu_codec.py
+++ /dev/null
@@ -1,54 +0,0 @@
-# -*- coding: utf-8 -*-
-# Copyright 2014 OpenMarket Ltd
-#
-# Licensed under the Apache License, Version 2.0 (the "License");
-# you may not use this file except in compliance with the License.
-# You may obtain a copy of the License at
-#
-#     http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS,
-# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-# See the License for the specific language governing permissions and
-# limitations under the License.
-
-from .units import Pdu
-
-import copy
-
-
-class PduCodec(object):
-
-    def __init__(self, hs):
-        self.signing_key = hs.config.signing_key[0]
-        self.server_name = hs.hostname
-        self.event_factory = hs.get_event_factory()
-        self.clock = hs.get_clock()
-        self.hs = hs
-
-    def event_from_pdu(self, pdu):
-        kwargs = {}
-
-        kwargs["etype"] = pdu.type
-
-        kwargs.update({
-            k: v
-            for k, v in pdu.get_full_dict().items()
-            if k not in [
-                "type",
-            ]
-        })
-
-        return self.event_factory.create_event(**kwargs)
-
-    def pdu_from_event(self, event):
-        d = event.get_full_dict()
-
-        kwargs = copy.deepcopy(event.unrecognized_keys)
-        kwargs.update({
-            k: v for k, v in d.items()
-        })
-
-        pdu = Pdu(**kwargs)
-        return pdu
diff --git a/synapse/federation/replication.py b/synapse/federation/replication.py
index a07e30784..8ee74de00 100644
--- a/synapse/federation/replication.py
+++ b/synapse/federation/replication.py
@@ -19,7 +19,7 @@ a given transport.
 
 from twisted.internet import defer
 
-from .units import Transaction, Pdu, Edu
+from .units import Transaction, Edu
 
 from .persistence import TransactionActions
 
@@ -72,6 +72,8 @@ class ReplicationLayer(object):
 
         self._clock = hs.get_clock()
 
+        self.event_factory = hs.get_event_factory()
+
     def set_handler(self, handler):
         """Sets the handler that the replication layer will use to communicate
         receipt of new PDUs from other home servers. The required methods are
@@ -203,7 +205,10 @@ class ReplicationLayer(object):
 
         transaction = Transaction(**transaction_data)
 
-        pdus = [Pdu(outlier=False, **p) for p in transaction.pdus]
+        pdus = [
+            self.event_from_pdu_json(p, outlier=False)
+            for p in transaction.pdus
+        ]
         for pdu in pdus:
             yield self._handle_new_pdu(dest, pdu, backfilled=True)
 
@@ -235,7 +240,10 @@ class ReplicationLayer(object):
 
         transaction = Transaction(**transaction_data)
 
-        pdu_list = [Pdu(outlier=outlier, **p) for p in transaction.pdus]
+        pdu_list = [
+            self.event_from_pdu_json(p, outlier=outlier)
+            for p in transaction.pdus
+        ]
 
         pdu = None
         if pdu_list:
@@ -265,8 +273,10 @@ class ReplicationLayer(object):
         )
 
         transaction = Transaction(**transaction_data)
-
-        pdus = [Pdu(outlier=True, **p) for p in transaction.pdus]
+        pdus = [
+            self.event_from_pdu_json(p, outlier=True)
+            for p in transaction.pdus
+        ]
 
         defer.returnValue(pdus)
 
@@ -293,7 +303,9 @@ class ReplicationLayer(object):
                 p["age_ts"] = int(self._clock.time_msec()) - int(p["age"])
                 del p["age"]
 
-        pdu_list = [Pdu(**p) for p in transaction.pdus]
+        pdu_list = [
+            self.event_from_pdu_json(p) for p in transaction.pdus
+        ]
 
         logger.debug("[%s] Got transaction", transaction.transaction_id)
 
@@ -388,30 +400,30 @@ class ReplicationLayer(object):
     def on_make_join_request(self, context, user_id):
         pdu = yield self.handler.on_make_join_request(context, user_id)
         defer.returnValue({
-            "event": pdu.get_dict(),
+            "event": pdu.get_pdu_json(),
         })
 
     @defer.inlineCallbacks
     def on_invite_request(self, origin, content):
-        pdu = Pdu(**content)
+        pdu = self.event_from_pdu_json(content)
         ret_pdu = yield self.handler.on_invite_request(origin, pdu)
         defer.returnValue(
             (
                 200,
                 {
-                    "event": ret_pdu.get_dict(),
+                    "event": ret_pdu.get_pdu_json(),
                 }
             )
         )
 
     @defer.inlineCallbacks
     def on_send_join_request(self, origin, content):
-        pdu = Pdu(**content)
+        pdu = self.event_from_pdu_json(content)
         res_pdus = yield self.handler.on_send_join_request(origin, pdu)
 
         defer.returnValue((200, {
-            "state": [p.get_dict() for p in res_pdus["state"]],
-            "auth_chain": [p.get_dict() for p in res_pdus["auth_chain"]],
+            "state": [p.get_pdu_json() for p in res_pdus["state"]],
+            "auth_chain": [p.get_pdu_json() for p in res_pdus["auth_chain"]],
         }))
 
     @defer.inlineCallbacks
@@ -421,7 +433,7 @@ class ReplicationLayer(object):
             (
                 200,
                 {
-                    "auth_chain": [a.get_dict() for a in auth_pdus],
+                    "auth_chain": [a.get_pdu_json() for a in auth_pdus],
                 }
             )
         )
@@ -438,7 +450,7 @@ class ReplicationLayer(object):
 
         logger.debug("Got response to make_join: %s", pdu_dict)
 
-        defer.returnValue(Pdu(**pdu_dict))
+        defer.returnValue(self.event_from_pdu_json(pdu_dict))
 
     @defer.inlineCallbacks
     def send_join(self, destination, pdu):
@@ -446,12 +458,15 @@ class ReplicationLayer(object):
             destination,
             pdu.room_id,
             pdu.event_id,
-            pdu.get_dict(),
+            pdu.get_pdu_json(),
         )
 
         logger.debug("Got content: %s", content)
 
-        state = [Pdu(outlier=True, **p) for p in content.get("state", [])]
+        state = [
+            self.event_from_pdu_json(p, outlier=True)
+            for p in content.get("state", [])
+        ]
 
         # FIXME: We probably want to do something with the auth_chain given
         # to us
@@ -468,14 +483,14 @@ class ReplicationLayer(object):
             destination=destination,
             context=context,
             event_id=event_id,
-            content=pdu.get_dict(),
+            content=pdu.get_pdu_json(),
         )
 
         pdu_dict = content["event"]
 
         logger.debug("Got response to send_invite: %s", pdu_dict)
 
-        defer.returnValue(Pdu(**pdu_dict))
+        defer.returnValue(self.event_from_pdu_json(pdu_dict))
 
     @log_function
     def _get_persisted_pdu(self, origin, event_id):
@@ -490,7 +505,7 @@ class ReplicationLayer(object):
         """Returns a new Transaction containing the given PDUs suitable for
         transmission.
         """
-        pdus = [p.get_dict() for p in pdu_list]
+        pdus = [p.get_pdu_json() for p in pdu_list]
         time_now = self._clock.time_msec()
         for p in pdus:
             if "age_ts" in p:
@@ -563,6 +578,14 @@ class ReplicationLayer(object):
     def __str__(self):
         return "<ReplicationLayer(%s)>" % self.server_name
 
+    def event_from_pdu_json(self, pdu_json, outlier=False):
+        #TODO: Check we have all the PDU keys here
+        pdu_json.setdefault("hashes", {})
+        pdu_json.setdefault("signatures", {})
+        return self.event_factory.create_event(
+            pdu_json["type"], outlier=outlier, **pdu_json
+        )
+
 
 class _TransactionQueue(object):
     """This class makes sure we only have one transaction in flight at
diff --git a/synapse/federation/units.py b/synapse/federation/units.py
index 70412439c..6e708edb8 100644
--- a/synapse/federation/units.py
+++ b/synapse/federation/units.py
@@ -25,83 +25,6 @@ import logging
 logger = logging.getLogger(__name__)
 
 
-class Pdu(JsonEncodedObject):
-    """ A Pdu represents a piece of data sent from a server and is associated
-    with a context.
-
-    A Pdu can be classified as "state". For a given context, we can efficiently
-    retrieve all state pdu's that haven't been clobbered. Clobbering is done
-    via a unique constraint on the tuple (context, type, state_key). A pdu
-    is a state pdu if `is_state` is True.
-
-    Example pdu::
-
-        {
-            "event_id": "$78c:example.com",
-            "origin_server_ts": 1404835423000,
-            "origin": "bar",
-            "prev_ids": [
-                ["23b", "foo"],
-                ["56a", "bar"],
-            ],
-            "content": { ... },
-        }
-
-    """
-
-    valid_keys = [
-        "event_id",
-        "room_id",
-        "origin",
-        "origin_server_ts",
-        "type",
-        "destinations",
-        "prev_events",
-        "depth",
-        "content",
-        "hashes",
-        "user_id",
-        "auth_events",
-        "signatures",  # Below this are keys valid only for State Pdus.
-        "state_key",
-        "prev_state",
-    ]
-
-    internal_keys = [
-        "destinations",
-        "transaction_id",
-        "outlier",
-    ]
-
-    required_keys = [
-        "event_id",
-        "room_id",
-        "origin",
-        "origin_server_ts",
-        "type",
-        "content",
-    ]
-
-    # TODO: We need to make this properly load content rather than
-    # just leaving it as a dict. (OR DO WE?!)
-
-    def __init__(self, destinations=[], prev_events=[],
-                 outlier=False, hashes={}, signatures={}, **kwargs):
-        super(Pdu, self).__init__(
-            destinations=destinations,
-            prev_events=prev_events,
-            outlier=outlier,
-            hashes=hashes,
-            signatures=signatures,
-            **kwargs
-        )
-
-    def __str__(self):
-        return "(%s, %s)" % (self.__class__.__name__, repr(self.__dict__))
-
-    def __repr__(self):
-        return "<%s, %s>" % (self.__class__.__name__, repr(self.__dict__))
-
 
 class Edu(JsonEncodedObject):
     """ An Edu represents a piece of data sent from one homeserver to another.
@@ -202,6 +125,6 @@ class Transaction(JsonEncodedObject):
         for p in pdus:
             p.transaction_id = kwargs["transaction_id"]
 
-        kwargs["pdus"] = [p.get_dict() for p in pdus]
+        kwargs["pdus"] = [p.get_pdu_json() for p in pdus]
 
         return Transaction(**kwargs)
diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py
index fc00128c5..da38f34e6 100644
--- a/synapse/handlers/federation.py
+++ b/synapse/handlers/federation.py
@@ -22,7 +22,6 @@ from synapse.api.errors import AuthError, FederationError, SynapseError
 from synapse.api.events.room import RoomMemberEvent
 from synapse.api.constants import Membership
 from synapse.util.logutils import log_function
-from synapse.federation.pdu_codec import PduCodec
 from synapse.util.async import run_on_reactor
 from synapse.crypto.event_signing import (
     compute_event_signature, check_event_content_hash
@@ -69,8 +68,6 @@ class FederationHandler(BaseHandler):
 
         self.replication_layer.set_handler(self)
 
-        self.pdu_codec = PduCodec(hs)
-
         # When joining a room we need to queue any events for that room up
         self.room_queues = {}
 
@@ -92,7 +89,7 @@ class FederationHandler(BaseHandler):
 
         yield run_on_reactor()
 
-        pdu = self.pdu_codec.pdu_from_event(event)
+        pdu = event
 
         if not hasattr(pdu, "destinations") or not pdu.destinations:
             pdu.destinations = []
@@ -105,7 +102,7 @@ class FederationHandler(BaseHandler):
         """ Called by the ReplicationLayer when we have a new pdu. We need to
         do auth checks and put it through the StateHandler.
         """
-        event = self.pdu_codec.event_from_pdu(pdu)
+        event = pdu
 
         logger.debug("Got event: %s", event.event_id)
 
@@ -118,18 +115,15 @@ class FederationHandler(BaseHandler):
         logger.debug("Processing event: %s", event.event_id)
 
         redacted_event = prune_event(event)
-        redacted_event.origin = pdu.origin
-        redacted_event.origin_server_ts = pdu.origin_server_ts
-        redacted_pdu = self.pdu_codec.pdu_from_event(redacted_event)
 
-        redacted_pdu_json = redacted_pdu.get_dict()
+        redacted_pdu_json = redacted_event.get_pdu_json()
         try:
             yield self.keyring.verify_json_for_server(
                 event.origin, redacted_pdu_json
             )
         except SynapseError as e:
             logger.warn("Signature check failed for %s redacted to %s",
-                encode_canonical_json(pdu.get_dict()),
+                encode_canonical_json(pdu.get_pdu_json()),
                 encode_canonical_json(redacted_pdu_json),
             )
             raise FederationError(
@@ -147,7 +141,7 @@ class FederationHandler(BaseHandler):
             event = redacted_event
 
         if state:
-            state = [self.pdu_codec.event_from_pdu(p) for p in state]
+            state = [p for p in state]
 
         is_new_state = yield self.state_handler.annotate_event_with_state(
             event,
@@ -239,7 +233,7 @@ class FederationHandler(BaseHandler):
         events = []
 
         for pdu in pdus:
-            event = self.pdu_codec.event_from_pdu(pdu)
+            event = pdu
 
             # FIXME (erikj): Not sure this actually works :/
             yield self.state_handler.annotate_event_with_state(event)
@@ -260,15 +254,15 @@ class FederationHandler(BaseHandler):
             destination=target_host,
             context=event.room_id,
             event_id=event.event_id,
-            pdu=self.pdu_codec.pdu_from_event(event)
+            pdu=event
         )
 
-        defer.returnValue(self.pdu_codec.event_from_pdu(pdu))
+        defer.returnValue(pdu)
 
     @defer.inlineCallbacks
     def on_event_auth(self, event_id):
         auth = yield self.store.get_auth_chain(event_id)
-        defer.returnValue([self.pdu_codec.pdu_from_event(e) for e in auth])
+        defer.returnValue([e for e in auth])
 
     @log_function
     @defer.inlineCallbacks
@@ -292,7 +286,7 @@ class FederationHandler(BaseHandler):
 
         logger.debug("Got response to make_join: %s", pdu)
 
-        event = self.pdu_codec.event_from_pdu(pdu)
+        event = pdu
 
         # We should assert some things.
         assert(event.type == RoomMemberEvent.TYPE)
@@ -310,10 +304,10 @@ class FederationHandler(BaseHandler):
 
             state = yield self.replication_layer.send_join(
                 target_host,
-                self.pdu_codec.pdu_from_event(event)
+                event
             )
 
-            state = [self.pdu_codec.event_from_pdu(p) for p in state]
+            state = [p for p in state]
 
             logger.debug("do_invite_join state: %s", state)
 
@@ -387,7 +381,7 @@ class FederationHandler(BaseHandler):
         yield self.auth.add_auth_events(event)
         self.auth.check(event, raises=True)
 
-        pdu = self.pdu_codec.pdu_from_event(event)
+        pdu = event
 
         defer.returnValue(pdu)
 
@@ -397,7 +391,7 @@ class FederationHandler(BaseHandler):
         """ We have received a join event for a room. Fully process it and
         respond with the current state and auth chains.
         """
-        event = self.pdu_codec.event_from_pdu(pdu)
+        event = pdu
 
         event.outlier = False
 
@@ -429,7 +423,7 @@ class FederationHandler(BaseHandler):
                     "user_joined_room", user=user, room_id=event.room_id
                 )
 
-        new_pdu = self.pdu_codec.pdu_from_event(event)
+        new_pdu = event
 
         destinations = set()
 
@@ -450,17 +444,10 @@ class FederationHandler(BaseHandler):
         yield self.replication_layer.send_pdu(new_pdu)
 
         auth_chain = yield self.store.get_auth_chain(event.event_id)
-        pdu_auth_chain = [
-            self.pdu_codec.pdu_from_event(e)
-            for e in auth_chain
-        ]
 
         defer.returnValue({
-            "state": [
-                self.pdu_codec.pdu_from_event(e)
-                for e in event.state_events.values()
-            ],
-            "auth_chain": pdu_auth_chain,
+            "state": event.state_events.values(),
+            "auth_chain": auth_chain,
         })
 
     @defer.inlineCallbacks
@@ -469,7 +456,7 @@ class FederationHandler(BaseHandler):
 
         Respond with the now signed event.
         """
-        event = self.pdu_codec.event_from_pdu(pdu)
+        event = pdu
 
         event.outlier = True
 
@@ -493,7 +480,7 @@ class FederationHandler(BaseHandler):
             event, extra_users=[target_user],
         )
 
-        defer.returnValue(self.pdu_codec.pdu_from_event(event))
+        defer.returnValue(event)
 
     @defer.inlineCallbacks
     def get_state_for_pdu(self, origin, room_id, event_id):
@@ -524,12 +511,7 @@ class FederationHandler(BaseHandler):
                 else:
                     del results[(event.type, event.state_key)]
 
-            defer.returnValue(
-                [
-                    self.pdu_codec.pdu_from_event(s)
-                    for s in results.values()
-                ]
-            )
+            defer.returnValue(results.values())
         else:
             defer.returnValue([])
 
@@ -546,10 +528,7 @@ class FederationHandler(BaseHandler):
             limit
         )
 
-        defer.returnValue([
-            self.pdu_codec.pdu_from_event(e)
-            for e in events
-        ])
+        defer.returnValue(events)
 
     @defer.inlineCallbacks
     @log_function
@@ -572,7 +551,7 @@ class FederationHandler(BaseHandler):
             if not in_room:
                 raise AuthError(403, "Host not in room.")
 
-            defer.returnValue(self.pdu_codec.pdu_from_event(event))
+            defer.returnValue(event)
         else:
             defer.returnValue(None)
 
diff --git a/synapse/storage/_base.py b/synapse/storage/_base.py
index 30e6eac8d..5d4be09a8 100644
--- a/synapse/storage/_base.py
+++ b/synapse/storage/_base.py
@@ -492,6 +492,14 @@ class SQLBaseStore(object):
                 for n, s in signatures.items()
             }
 
+            hashes = self._get_event_content_hashes_txn(
+                txn, ev.event_id,
+            )
+
+            ev.hashes = {
+                k: encode_base64(v) for k, v in hashes.items()
+            }
+
             prevs = self._get_prev_events_and_state(txn, ev.event_id)
 
             ev.prev_events = [
diff --git a/tests/federation/test_federation.py b/tests/federation/test_federation.py
index ad09fab39..efac4075d 100644
--- a/tests/federation/test_federation.py
+++ b/tests/federation/test_federation.py
@@ -23,7 +23,7 @@ from ..utils import MockHttpResource, MockClock, MockKey
 
 from synapse.server import HomeServer
 from synapse.federation import initialize_http_replication
-from synapse.federation.units import Pdu
+from synapse.api.events import SynapseEvent
 
 
 def make_pdu(prev_pdus=[], **kwargs):
@@ -40,7 +40,7 @@ def make_pdu(prev_pdus=[], **kwargs):
     }
     pdu_fields.update(kwargs)
 
-    return Pdu(prev_pdus=prev_pdus, **pdu_fields)
+    return SynapseEvent(prev_pdus=prev_pdus, **pdu_fields)
 
 
 class FederationTestCase(unittest.TestCase):
@@ -169,7 +169,7 @@ class FederationTestCase(unittest.TestCase):
             (200, "OK")
         )
 
-        pdu = Pdu(
+        pdu = SynapseEvent(
             event_id="abc123def456",
             origin="red",
             room_id="my-context",
@@ -189,7 +189,7 @@ class FederationTestCase(unittest.TestCase):
                 "origin_server_ts": 1000000,
                 "origin": "test",
                 "pdus": [
-                    pdu.get_dict(),
+                    pdu.get_pdu_json(),
                 ],
                 'pdu_failures': [],
             },
diff --git a/tests/handlers/test_federation.py b/tests/handlers/test_federation.py
index 3f17ca8fb..e19b07381 100644
--- a/tests/handlers/test_federation.py
+++ b/tests/handlers/test_federation.py
@@ -19,9 +19,10 @@ from tests import unittest
 from synapse.api.events.room import (
     MessageEvent,
 )
+
+from synapse.api.events import SynapseEvent
 from synapse.handlers.federation import FederationHandler
 from synapse.server import HomeServer
-from synapse.federation.units import Pdu
 
 from mock import NonCallableMock, ANY, Mock
 
@@ -74,7 +75,7 @@ class FederationTestCase(unittest.TestCase):
 
     @defer.inlineCallbacks
     def test_msg(self):
-        pdu = Pdu(
+        pdu = SynapseEvent(
             type=MessageEvent.TYPE,
             room_id="foo",
             content={"msgtype": u"fooo"},