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# Pleroma: A lightweight social networking server
# Copyright © 2017-2022 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

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