diff --git a/lib/matrix_server.ex b/lib/matrix_server.ex
index 4cc0a2f..e77af16 100644
--- a/lib/matrix_server.ex
+++ b/lib/matrix_server.ex
@@ -38,7 +38,6 @@ defmodule MatrixServer do
     end
   end
 
-  # TODO Eventually move to regex with named captures.
   @spec get_localpart(String.t()) :: String.t() | nil
   def get_localpart(id) do
     with [part, _] <- String.split(id, ":", parts: 2),
@@ -85,17 +84,25 @@ defmodule MatrixServer do
   # https://stackoverflow.com/questions/41523762/41671211
   @spec to_serializable_map(struct()) :: map()
   def to_serializable_map(struct) do
-    association_fields = struct.__struct__.__schema__(:associations)
+    association_fields =
+      if Kernel.function_exported?(struct.__struct__, :__schema__, 1) do
+        struct.__struct__.__schema__(:associations)
+      else
+        []
+      end
+
     waste_fields = association_fields ++ [:__meta__]
 
     struct
     |> Map.from_struct()
-    |> Map.drop(waste_fields)
+    |> Enum.reject(fn {k, v} ->
+      is_nil(v) or k in waste_fields
+    end)
+    |> Enum.into(%{})
   end
 
   @spec serialize_and_encode(struct()) :: {:ok, String.t()} | {:error, Jason.EncodeError.t()}
   def serialize_and_encode(struct) do
-    # TODO: handle nil values in struct?
     struct
     |> to_serializable_map()
     |> encode_canonical_json()
diff --git a/lib/matrix_server/encodable_map.ex b/lib/matrix_server/encodable_map.ex
index 3d98b29..e48a8e8 100644
--- a/lib/matrix_server/encodable_map.ex
+++ b/lib/matrix_server/encodable_map.ex
@@ -1,6 +1,6 @@
 # https://github.com/michalmuskala/jason/issues/69
 defmodule MatrixServer.EncodableMap do
-  alias MatrixServer.EncodableMap
+  alias MatrixServer.{EncodableMap, Event}
   alias MatrixServer.Types.{UserId, RoomId, EventId, GroupId, AliasId}
 
   defstruct pairs: []
@@ -15,12 +15,10 @@ defmodule MatrixServer.EncodableMap do
     pairs =
       map
       |> Enum.map(fn
-        {k, v} when is_struct(v, DateTime) ->
-          {k, DateTime.to_unix(v, :millisecond)}
-
         {k, v}
         when is_struct(v, UserId) or is_struct(v, RoomId) or is_struct(v, EventId) or
                is_struct(v, GroupId) or is_struct(v, AliasId) ->
+          # Simply convert IDs to a string.
           {k, to_string(v)}
 
         {k, v} when is_map(v) ->
diff --git a/lib/matrix_server/key_server.ex b/lib/matrix_server/key_server.ex
index 39b4e07..fe80da5 100644
--- a/lib/matrix_server/key_server.ex
+++ b/lib/matrix_server/key_server.ex
@@ -48,6 +48,8 @@ defmodule MatrixServer.KeyServer do
     object = Map.drop(object, [:signatures, :unsigned])
 
     with {:ok, json} <- MatrixServer.encode_canonical_json(object) do
+      IO.puts(json)
+
       signature =
         json
         |> :enacl.sign_detached(private_key)
diff --git a/lib/matrix_server/room_server.ex b/lib/matrix_server/room_server.ex
index 97fccaa..58cfa63 100644
--- a/lib/matrix_server/room_server.ex
+++ b/lib/matrix_server/room_server.ex
@@ -18,6 +18,9 @@ defmodule MatrixServer.RoomServer do
     GenServer.start_link(__MODULE__, opts, name: name)
   end
 
+  @spec get_room_server(Room.t()) :: {:error, :not_found} | DynamicSupervisor.on_start_child()
+  def get_room_server(%Room{id: room_id}), do: get_room_server(room_id)
+
   # Get room server pid, or spin one up for the room.
   # If the room does not exist, return an error.
   @spec get_room_server(String.t()) :: {:error, :not_found} | DynamicSupervisor.on_start_child()
diff --git a/lib/matrix_server/schema/event.ex b/lib/matrix_server/schema/event.ex
index edd35e7..7f5eeda 100644
--- a/lib/matrix_server/schema/event.ex
+++ b/lib/matrix_server/schema/event.ex
@@ -9,7 +9,7 @@ defmodule MatrixServer.Event do
   # TODO: Could refactor to also always set prev_events, but not necessary.
   @type t :: %__MODULE__{
           type: String.t(),
-          origin_server_ts: DateTime.t(),
+          origin_server_ts: integer(),
           state_key: String.t(),
           sender: UserId.t(),
           content: map(),
@@ -23,7 +23,7 @@ defmodule MatrixServer.Event do
   @primary_key {:event_id, :string, []}
   schema "events" do
     field :type, :string
-    field :origin_server_ts, :utc_datetime_usec
+    field :origin_server_ts, :integer
     field :state_key, :string
     field :sender, UserId
     field :content, :map
@@ -36,12 +36,38 @@ defmodule MatrixServer.Event do
     belongs_to :room, Room, type: :string
   end
 
+  defimpl Jason.Encoder, for: Event do
+    @pdu_keys [
+      :auth_events,
+      :content,
+      :depth,
+      :hashes,
+      :origin,
+      :origin_server_ts,
+      :prev_events,
+      :redacts,
+      :room_id,
+      :sender,
+      :signatures,
+      :state_key,
+      :type,
+      :unsigned
+    ]
+
+    def encode(event, opts) do
+      event
+      |> Map.take(@pdu_keys)
+      |> Map.update!(:sender, &Kernel.to_string/1)
+      |> Jason.Encode.map(opts)
+    end
+  end
+
   @spec new(Room.t(), Account.t()) :: %Event{}
   def new(%Room{id: room_id}, %Account{localpart: localpart}) do
     %Event{
       room_id: room_id,
       sender: %UserId{localpart: localpart, domain: MatrixServer.server_name()},
-      origin_server_ts: DateTime.utc_now(),
+      origin_server_ts: DateTime.utc_now() |> DateTime.to_unix(:millisecond),
       prev_events: [],
       auth_events: []
     }
diff --git a/lib/matrix_server/schema/server_key_info.ex b/lib/matrix_server/schema/server_key_info.ex
index 9248697..539ac67 100644
--- a/lib/matrix_server/schema/server_key_info.ex
+++ b/lib/matrix_server/schema/server_key_info.ex
@@ -10,7 +10,7 @@ defmodule MatrixServer.ServerKeyInfo do
 
   @primary_key {:server_name, :string, []}
   schema "server_key_info" do
-    field :valid_until, :utc_datetime
+    field :valid_until, :integer
 
     has_many :signing_keys, SigningKey, foreign_key: :server_name
   end
@@ -43,7 +43,7 @@ defmodule MatrixServer.ServerKeyInfo do
             verify_keys: verify_keys,
             valid_until_ts: valid_until_ts
           }} <- HTTPClient.get_signing_keys(client),
-         {:ok, valid_until} <- DateTime.from_unix(valid_until_ts) do
+         {:ok, valid_until} <- DateTime.from_unix(valid_until_ts, :millisecond) do
       signing_keys =
         Enum.map(verify_keys, fn {key_id, %{"key" => key}} ->
           [server_name: server_name, signing_key_id: key_id, signing_key: key]
@@ -52,7 +52,8 @@ defmodule MatrixServer.ServerKeyInfo do
       # Always check every week to prevent misuse.
       ski = %ServerKeyInfo{
         server_name: server_name,
-        valid_until: MatrixServer.min_datetime(in_a_week, valid_until)
+        valid_until:
+          MatrixServer.min_datetime(in_a_week, valid_until) |> DateTime.to_unix(:millisecond)
       }
 
       case upsert_multi(server_name, ski, signing_keys) |> Repo.transaction() do
diff --git a/lib/matrix_server/types/user_id.ex b/lib/matrix_server/types/user_id.ex
index 2754fbc..1797a68 100644
--- a/lib/matrix_server/types/user_id.ex
+++ b/lib/matrix_server/types/user_id.ex
@@ -18,6 +18,12 @@ defmodule MatrixServer.Types.UserId do
     end
   end
 
+  defimpl Jason.Encoder, for: UserId do
+    def encode(user_id, opts) do
+      Jason.Encode.string(to_string(user_id), opts)
+    end
+  end
+
   def type(), do: :string
 
   def cast(s) when is_binary(s) do
diff --git a/lib/matrix_server_web/error.ex b/lib/matrix_server_web/error.ex
index 7f93163..257edba 100644
--- a/lib/matrix_server_web/error.ex
+++ b/lib/matrix_server_web/error.ex
@@ -12,6 +12,7 @@ defmodule MatrixServerWeb.Error do
     invalid_room_state:
       {400, "M_INVALID_ROOM_STATE", "The request would leave the room in an invalid state."},
     unauthorized: {400, "M_UNAUTHORIZED", "The request was unauthorized."},
+    invalid_param: {400, "M_INVALID_PARAM", "A request parameter was invalid."},
     unknown_token: {401, "M_UNKNOWN_TOKEN", "Invalid access token."},
     missing_token: {401, "M_MISSING_TOKEN", "Access token required."},
     not_found: {404, "M_NOT_FOUND", "The requested resource was not found."},
diff --git a/lib/matrix_server_web/federation/authenticate_server.ex b/lib/matrix_server_web/federation/authenticate_server.ex
index 85ef3ff..247af30 100644
--- a/lib/matrix_server_web/federation/authenticate_server.ex
+++ b/lib/matrix_server_web/federation/authenticate_server.ex
@@ -12,8 +12,18 @@ defmodule MatrixServerWeb.Federation.AuthenticateServer do
         method: method,
         query_string: query_string
       }) do
+    # TODO: This will break if request ends with '?'.
+    uri = URI.decode_www_form(path)
+
+    uri =
+      if String.length(query_string) > 0 do
+        uri <> "?" <> URI.decode_www_form(query_string)
+      else
+        uri
+      end
+
     object_to_sign = %{
-      uri: path <> "?" <> URI.decode_www_form(query_string),
+      uri: uri,
       method: method,
       destination: MatrixServer.server_name()
     }
@@ -39,6 +49,7 @@ defmodule MatrixServerWeb.Federation.AuthenticateServer do
              ServerKeyInfo.with_fresh_signing_keys(origin) do
         Enum.find_value(keys, false, fn %SigningKey{signing_key: signing_key} ->
           with {:ok, decoded_key} <- MatrixServer.decode_base64(signing_key) do
+            IO.puts(encoded_object)
             MatrixServer.sign_verify(raw_sig, encoded_object, decoded_key)
           else
             _ -> false
diff --git a/lib/matrix_server_web/federation/controllers/event_controller.ex b/lib/matrix_server_web/federation/controllers/event_controller.ex
index 9721a0d..a447cfa 100644
--- a/lib/matrix_server_web/federation/controllers/event_controller.ex
+++ b/lib/matrix_server_web/federation/controllers/event_controller.ex
@@ -2,9 +2,44 @@ defmodule MatrixServerWeb.Federation.EventController do
   use MatrixServerWeb, :controller
   use MatrixServerWeb.Federation.AuthenticateServer
 
-  def event(conn, %{"event_id" => _event_id}) do
-    conn
-    |> put_status(200)
-    |> json(%{})
+  import MatrixServerWeb.Error
+  import Ecto.Query
+
+  alias MatrixServer.{Repo, Event, RoomServer}
+  alias MatrixServerWeb.Federation.Transaction
+
+  def event(%Plug.Conn{assigns: %{origin: origin}} = conn, %{"event_id" => event_id}) do
+    query =
+      Event
+      |> where([e], e.event_id == ^event_id)
+      |> preload(:room)
+
+    case Repo.one(query) do
+      %Event{room: room} = event ->
+        case RoomServer.get_room_server(room) do
+          {:ok, pid} ->
+            if RoomServer.server_in_room(pid, origin) do
+              data = Transaction.new([event])
+
+              conn
+              |> put_status(200)
+              |> json(data)
+            else
+              put_error(
+                conn,
+                :unauthorized,
+                "Origin server is not allowed to see requested event."
+              )
+            end
+
+          _ ->
+            put_error(conn, :unknown)
+        end
+
+      nil ->
+        put_error(conn, :not_found, "Event or room not found.")
+    end
   end
+
+  def event(conn, _), do: put_error(conn, :bad_json)
 end
diff --git a/lib/matrix_server_web/federation/controllers/key_controller.ex b/lib/matrix_server_web/federation/controllers/key_controller.ex
index 4d14175..243e44b 100644
--- a/lib/matrix_server_web/federation/controllers/key_controller.ex
+++ b/lib/matrix_server_web/federation/controllers/key_controller.ex
@@ -20,7 +20,7 @@ defmodule MatrixServerWeb.Federation.KeyController do
       server_name: MatrixServer.server_name(),
       verify_keys: keys,
       old_verify_keys: %{},
-      valid_until_ts: valid_until
+      valid_until_ts: DateTime.to_unix(valid_until, :millisecond)
     }
 
     case KeyServer.sign_object(data) do
diff --git a/lib/matrix_server_web/federation/http_client.ex b/lib/matrix_server_web/federation/http_client.ex
index e2eab15..ec4f424 100644
--- a/lib/matrix_server_web/federation/http_client.ex
+++ b/lib/matrix_server_web/federation/http_client.ex
@@ -29,7 +29,9 @@ defmodule MatrixServerWeb.Federation.HTTPClient do
     with {:ok,
           %GetSigningKeys{server_name: server_name, verify_keys: verify_keys, signatures: sigs} =
             response} <- tesla_request(:get, client, path, GetSigningKeys),
-         {:ok, encoded_body} <- MatrixServer.serialize_and_encode(response),
+         serializable_response <- MatrixServer.to_serializable_map(response),
+         serializable_response <- Map.drop(serializable_response, [:signatures]),
+         {:ok, encoded_body} <- MatrixServer.encode_canonical_json(serializable_response),
          server_sigs when not is_nil(server_sigs) <- sigs[server_name] do
       # For each verify key, check if there is a matching signature.
       # If not, invalidate the whole response.
@@ -58,12 +60,20 @@ defmodule MatrixServerWeb.Federation.HTTPClient do
     Tesla.get(client, path)
   end
 
+  def get_event(client, event_id) do
+    path = RouteHelpers.event_path(Endpoint, :event, event_id)
+
+    Tesla.get(client, path)
+  end
+
   defp tesla_request(method, client, path, request_schema) do
     with {:ok, %Tesla.Env{body: body}} <- Tesla.request(client, url: path, method: method),
          %Ecto.Changeset{valid?: true} = cs <- apply(request_schema, :changeset, [body]) do
       {:ok, Ecto.Changeset.apply_changes(cs)}
     else
-      _ -> :error
+      x ->
+        IO.inspect(x)
+        :error
     end
   end
 end
diff --git a/lib/matrix_server_web/federation/transaction.ex b/lib/matrix_server_web/federation/transaction.ex
new file mode 100644
index 0000000..6e2cd6b
--- /dev/null
+++ b/lib/matrix_server_web/federation/transaction.ex
@@ -0,0 +1,36 @@
+defmodule MatrixServerWeb.Federation.Transaction do
+  alias MatrixServer.Event
+  alias MatrixServerWeb.Federation.Transaction
+
+  # TODO
+  @type edu :: any()
+
+  @type t :: %__MODULE__{
+    origin: String.t(),
+    origin_server_ts: integer(),
+    pdus: [Event.t()],
+    edus: [edu()] | nil
+  }
+
+  defstruct [:origin, :origin_server_ts, :pdus, :edus]
+
+  defimpl Jason.Encoder, for: Transaction do
+    @fields [:origin, :origin_server_ts, :pdus, :edus]
+
+    def encode(transaction, opts) do
+      transaction
+      |> Map.take(@fields)
+      |> Jason.Encode.map(opts)
+    end
+  end
+
+  @spec new([Event.t()], [edu()] | nil) :: t()
+  def new(pdu_events, edus \\ nil) do
+    %Transaction{
+      origin: MatrixServer.server_name(),
+      origin_server_ts: System.os_time(:millisecond),
+      pdus: Enum.map(pdu_events, &MatrixServer.to_serializable_map/1),
+      edus: edus
+    }
+  end
+end
diff --git a/priv/repo/migrations/20210820184601_move_timestamps_to_ints_again.exs b/priv/repo/migrations/20210820184601_move_timestamps_to_ints_again.exs
new file mode 100644
index 0000000..b834440
--- /dev/null
+++ b/priv/repo/migrations/20210820184601_move_timestamps_to_ints_again.exs
@@ -0,0 +1,15 @@
+defmodule MatrixServer.Repo.Migrations.MoveTimestampsToIntsAgain do
+  use Ecto.Migration
+
+  def change do
+    alter table(:events) do
+      remove :origin_server_ts, :utc_datetime_usec, null: false
+      add :origin_server_ts, :bigint, null: false
+    end
+
+    alter table(:server_key_info) do
+      remove :valid_until, :utc_datetime_usec, null: false
+      add :valid_until, :bigint, default: 0, null: false
+    end
+  end
+end