RC4 encryption/decryption in Elixir/Erlang

enc.ex

# Install https://github.com/rubencaro/cipher first
require Cipher.Helpers, as: H

defmodule Enc do
  @random_key H.env(:keyphrase) |> Cipher.Digest.generate_key

  def stream_encrypt(xml) do
    {_, result} =
      :crypto.stream_init(:rc4, @random_key)
      |> :crypto.stream_encrypt(xml)

    Base.encode64(result)
  end

  def stream_decrypt(encoded_data, encoded_env_key) do
    {:ok, data} = Base.decode64(encoded_data)
    {:ok, env_key} = Base.decode64(encoded_env_key)

    random_key = :public_key.decrypt_private(env_key, private_key)

    {_, result} =
      :crypto.stream_init(:rc4, random_key)
      |> :crypto.stream_decrypt(data)

    result
  end

  def env_key do
    :public_key.encrypt_public(@random_key, public_key)
    |> Base.encode64
  end


  # Check this comment to see what's going on
  # https://github.com/potatosalad/erlang-jose/issues/13#issuecomment-160718744
  defp private_key do
    {:ok, pem_bin} = File.read "prv.key"

    pem_key = decode_key(pem_bin)
    private_key = elem(pem_key, 3)

    :public_key.der_decode(:RSAPrivateKey, private_key)
  end

  defp public_key do
    {:ok, pem_bin} = File.read "pub.pem"

    pem_bin |> decode_key
  end

  defp decode_key(key) do
    key
    |> :public_key.pem_decode
    |> hd
    |> :public_key.pem_entry_decode
  end
end