defmodule Pleroma.Captcha do alias Plug.Crypto.KeyGenerator alias Plug.Crypto.MessageEncryptor alias Calendar.DateTime use GenServer @doc false def start_link() do GenServer.start_link(__MODULE__, [], name: __MODULE__) end @doc false def init(_) do {:ok, nil} end @doc """ Ask the configured captcha service for a new captcha """ def new() do GenServer.call(__MODULE__, :new) end @doc """ Ask the configured captcha service to validate the captcha """ def validate(token, captcha, answer_data) do GenServer.call(__MODULE__, {:validate, token, captcha, answer_data}) end @doc false def handle_call(:new, _from, state) do enabled = Pleroma.Config.get([__MODULE__, :enabled]) if !enabled do {:reply, %{type: :none}, state} else new_captcha = method().new() secret_key_base = Pleroma.Config.get!([Pleroma.Web.Endpoint, :secret_key_base]) # This make salt a little different for two keys token = new_captcha[:token] secret = KeyGenerator.generate(secret_key_base, token <> "_encrypt") sign_secret = KeyGenerator.generate(secret_key_base, token <> "_sign") # Basicallty copy what Phoenix.Token does here, add the time to # the actual data and make it a binary to then encrypt it encrypted_captcha_answer = %{ at: DateTime.now_utc(), answer_data: new_captcha[:answer_data] } |> :erlang.term_to_binary() |> MessageEncryptor.encrypt(secret, sign_secret) { :reply, # Repalce the answer with the encrypted answer %{new_captcha | answer_data: encrypted_captcha_answer}, state } end end @doc false def handle_call({:validate, token, captcha, answer_data}, _from, state) do secret_key_base = Pleroma.Config.get!([Pleroma.Web.Endpoint, :secret_key_base]) secret = KeyGenerator.generate(secret_key_base, token <> "_encrypt") sign_secret = KeyGenerator.generate(secret_key_base, token <> "_sign") # If the time found is less than (current_time - seconds_valid), then the time has already passed. # Later we check that the time found is more than the presumed invalidatation time, that means # that the data is still valid and the captcha can be checked seconds_valid = Pleroma.Config.get!([Pleroma.Captcha, :seconds_valid]) valid_if_after = DateTime.subtract!(DateTime.now_utc(), seconds_valid) result = with {:ok, data} <- MessageEncryptor.decrypt(answer_data, secret, sign_secret), %{at: at, answer_data: answer_md5} <- :erlang.binary_to_term(data) do try do if DateTime.before?(at, valid_if_after), do: throw({:error, "CAPTCHA expired"}) if not is_nil(Cachex.get!(:used_captcha_cache, token)), do: throw({:error, "CAPTCHA already used"}) res = method().validate(token, captcha, answer_md5) # Throw if an error occurs if res != :ok, do: throw(res) # Mark this captcha as used {:ok, _} = Cachex.put(:used_captcha_cache, token, true, ttl: :timer.seconds(seconds_valid)) :ok catch :throw, e -> e end else _ -> {:error, "Invalid answer data"} end {:reply, result, state} end defp method, do: Pleroma.Config.get!([__MODULE__, :method]) end