Parse NTS-KE response

lib/chronoscope/gemini.ex

@@ -1,3 +1,2 @@
 defmodule Chronoscope.Gemini do
-
 end

lib/chronoscope/nts.ex

@@ -1,3 +1,38 @@
 defmodule Chronoscope.NTS do
- 
+  require Logger
+
+  alias Chronoscope.NTS.KeyEstablishment
+
+  @timeout_in_milliseconds 3000
+
+  def key_establishment(host, port) do
+    tls_options = :tls_certificate_check.options(host) ++ [alpn_advertised_protocols: ["ntske/1"]]
+
+    case :ssl.connect(host, port, tls_options, @timeout_in_milliseconds) do
+      {:ok, socket} -> perform_key_establishment(socket)
+      {:error, {:tls_alert, {:handshake_failure, error}}} -> {:error, to_string(error)}
+      {:error, error} -> {:error, inspect(error)}
+      error -> {:error, inspect(error)}
+    end
+  end
+
+  defp perform_key_establishment(socket) do
+    :ok = :ssl.send(socket, KeyEstablishment.request())
+
+    receive do
+      {:ssl, _socket, response} ->
+        :ssl.close(socket)
+        KeyEstablishment.parse_response(response)
+
+      msg ->
+        :ssl.close(socket)
+        Logger.error("received unexpected message: #{inspect(msg)}")
+        {:error, :no_response}
+    after
+      @timeout_in_milliseconds ->
+        :ssl.close(socket)
+        Logger.error("timed out waiting for response")
+        {:error, :timeout}
+    end
+  end
 end

lib/chronoscope/nts/key_establishment.ex

@@ -0,0 +1,90 @@
+defmodule Chronoscope.NTS.KeyEstablishment do
+  import Bitwise
+
+  @next_protocol_negotiation <<0x80, 0x01, 0x00, 0x02, 0x00, 0x00>>
+  @aead_algorithm_negotiation <<0x80, 0x04, 0x00, 0x04, 0x00, 0x1E, 0x00, 0x0F>>
+  @end_of_message <<0x80, 0x00, 0x00, 0x00>>
+
+  def request() do
+    @next_protocol_negotiation <> @aead_algorithm_negotiation <> @end_of_message
+  end
+
+  def parse_response(response) do
+    {:ok, Map.update(do_parse_response(response, %{}), :cookies, 0, &length/1)}
+  end
+
+  defp do_parse_response([], acc) do
+    acc
+  end
+
+  defp do_parse_response([0x80, 0x00, 0x00, 0x00], acc) do
+    acc
+  end
+
+  defp do_parse_response([0x80, 0x01, length_high, length_low | rest], acc) do
+    length = combine_octets(length_high, length_low)
+    {next_protocols, remaining} = Enum.split(rest, length)
+
+    do_parse_response(
+      remaining,
+      Map.put(acc, :next_protocols, parse_next_protocol(next_protocols))
+    )
+  end
+
+  defp do_parse_response([first, 0x04, length_high, length_low | rest], acc)
+       when first == 0x00 or first == 0x80 do
+    length = combine_octets(length_high, length_low)
+    {aead_algorithms, remaining} = Enum.split(rest, length)
+
+    do_parse_response(
+      remaining,
+      Map.put(acc, :aead_algorithms, parse_aead_algorithm(aead_algorithms))
+    )
+  end
+
+  defp do_parse_response([first, 0x05, length_high, length_low | rest], acc)
+       when first == 0x00 or first == 0x80 do
+    length = combine_octets(length_high, length_low)
+    {cookie, remaining} = Enum.split(rest, length)
+
+    do_parse_response(
+      remaining,
+      acc
+      |> Map.update(:cookies, [cookie], &[cookie | &1])
+      |> Map.put(:cookie_length, length)
+    )
+  end
+
+  defp do_parse_response([_, _, length_high, length_low | rest], acc) do
+    length = combine_octets(length_high, length_low)
+    {_, remaining} = Enum.split(rest, length)
+
+    do_parse_response(remaining, acc)
+  end
+
+  defp parse_aead_algorithm([0x00, 0x0F]) do
+    "AEAD_AES_SIV_CMAC_256"
+  end
+
+  defp parse_aead_algorithm([0x00, 0x1E]) do
+    "AEAD_AES_128_GCM_SIV"
+  end
+
+  defp parse_aead_algorithm(_aead_algorithm) do
+    "UNKNOWN"
+  end
+
+  defp parse_next_protocol([0x00, 0x00]) do
+    "NTPv4"
+  end
+
+  defp parse_next_protocol(_next_protocol) do
+    "UNASSIGNED"
+  end
+
+  # todo parse server/port information
+
+  defp combine_octets(high, low) do
+    high <<< 8 ||| low
+  end
+end

lib/chronoscope/nts/key_exchange.ex

@@ -1,2 +0,0 @@
-defmodule Chronoscope.NTS.KeyExchange do
-end

lib/chronoscope_web/controllers/api/nts/key_exchange_controller.ex

@@ -3,58 +3,23 @@ defmodule ChronoscopeWeb.API.NTS.KeyExchangeController do
 
   require Logger
 
+  alias Chronoscope.NTS
+
   @default_port "4460"
-  @timeout_in_milliseconds 3000
 
   def get(conn, params) do
     host = to_charlist(params["host"])
     port = String.to_integer(params["port"] || @default_port)
 
-    tls_options = :tls_certificate_check.options(host) ++ [alpn_advertised_protocols: ["ntse/1"]]
-
-    case :ssl.connect(host, port, tls_options, @timeout_in_milliseconds) do
-      {:ok, socket} ->
-        key_exchange_request =
-          <<0x80, 0x01, 0x00, 0x02, 0x00, 0x00, 0x80, 0x04, 0x00, 0x04, 0x00, 0x1E, 0x00, 0x0F,
-            0x80, 0x00, 0x00, 0x00>>
-
-        :ok = :ssl.send(socket, key_exchange_request)
-
-        receive do
-          {:ssl, _socket, data} ->
-            :ssl.close(socket)
-            ok_response(conn, %{status: :ok, response: parse_response(data)})
-
-          msg ->
-            :ssl.close(socket)
-            Logger.error("received unexpected message: #{inspect(msg)}")
-            ok_response(conn, %{status: :error, reason: :no_response})
-        after
-          @timeout_in_milliseconds ->
-            :ssl.close(socket)
-            Logger.error("timed out waiting for response")
-            ok_response(conn, %{status: :error, reason: :timeout})
-        end
-
-      {:error, {:tls_alert, {:handshake_failure, error}}} ->
-        ok_response(conn, %{status: :error, reason: to_string(error)})
+    case NTS.key_establishment(host, port) do
+      {:ok, configuration} ->
+        ok_response(conn, %{status: :ok, configuration: configuration})
 
       {:error, error} ->
         ok_response(conn, %{status: :error, reason: inspect(error)})
-
-      error ->
-        ok_response(conn, %{status: :error, reason: inspect(error)})
     end
   end
 
-  defp parse_response([0x80 | _] = _data) do
-    "success"
-  end
-
-  defp parse_response(_data) do
-    "failure"
-  end
-
   defp ok_response(conn, body) do
     conn
     |> Plug.Conn.put_resp_content_type("application/json")