# Pleroma: A lightweight social networking server # Copyright © 2017-2021 Pleroma Authors <https://pleroma.social/> # SPDX-License-Identifier: AGPL-3.0-only defmodule Pleroma.Captcha do alias Calendar.DateTime alias Plug.Crypto.KeyGenerator alias Plug.Crypto.MessageEncryptor @cachex Pleroma.Config.get([:cachex, :provider], Cachex) @doc """ Ask the configured captcha service for a new captcha """ def new do if not enabled?() do %{type: :none} else new_captcha = method().new() # This make salt a little different for two keys {secret, sign_secret} = secret_pair(new_captcha[:token]) # Basically 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) # Replace the answer with the encrypted answer %{new_captcha | answer_data: encrypted_captcha_answer} end end @doc """ Ask the configured captcha service to validate the captcha """ def validate(token, captcha, answer_data) do with {:ok, %{at: at, answer_data: answer_md5}} <- validate_answer_data(token, answer_data), :ok <- validate_expiration(at), :ok <- validate_usage(token), :ok <- method().validate(token, captcha, answer_md5), {:ok, _} <- mark_captcha_as_used(token) do :ok end end def enabled?, do: Pleroma.Config.get([__MODULE__, :enabled], false) defp seconds_valid, do: Pleroma.Config.get!([__MODULE__, :seconds_valid]) defp secret_pair(token) 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") {secret, sign_secret} end defp validate_answer_data(token, answer_data) do {secret, sign_secret} = secret_pair(token) with false <- is_nil(answer_data), {:ok, data} <- MessageEncryptor.decrypt(answer_data, secret, sign_secret), %{at: at, answer_data: answer_md5} <- :erlang.binary_to_term(data) do {:ok, %{at: at, answer_data: answer_md5}} else _ -> {:error, :invalid_answer_data} end end defp validate_expiration(created_at) do # 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 valid_if_after = DateTime.subtract!(DateTime.now_utc(), seconds_valid()) if DateTime.before?(created_at, valid_if_after) do {:error, :expired} else :ok end end defp validate_usage(token) do if is_nil(@cachex.get!(:used_captcha_cache, token)) do :ok else {:error, :already_used} end end defp mark_captcha_as_used(token) do ttl = seconds_valid() |> :timer.seconds() @cachex.put(:used_captcha_cache, token, true, ttl: ttl) end defp method, do: Pleroma.Config.get!([__MODULE__, :method]) end