Elixir Telegram

telegram.exs

use Bitwise

defmodule Telegram do
  use Bitwise

  @byte 8
  @bloc_size 4 * @byte

  def get_bloc(telegram, bloc_nr) do
    <<bloc::size(32)>> = binary_part(telegram, 2 + (bloc_nr - 1) * 4, 4)
    bloc
  end

  def get_byte(telegram, byte_nr) do
    <<byte::size(8)>> = binary_part(telegram, byte_nr, 1)
    byte
  end

  def decode(telegram, byte, max_byte, register, out) when byte == max_byte, do: out
  def decode(telegram, byte, max_byte, register, out \\ <<>>) do
    {new_register, pout} = decode_single(0, 8, register, 0)
    new_byte = get_byte(telegram, byte) ^^^ pout
    decode(telegram, byte + 1, max_byte, new_register, out <> <<new_byte>>)
  end

  def decode_single(count, max_count, register, pout) when count == max_count, do: {register, pout}
  def decode_single(count, max_count, register, pout) do
    out = 0
    |> maybe_xor(register &&& 0x00000002)
    |> maybe_xor(register &&& 0x00000004)
    |> maybe_xor(register &&& 0x00000800)
    |> maybe_xor(register &&& 0x80000000)
    register = (register <<< 1) + out
    pout = (pout <<< 1) + out

    decode_single(count + 1, max_count, register, pout)
  end

  defp maybe_xor(input, condition) do
    if condition > 0, do: input ^^^ 1, else: input
  end
end


raw_telegram = "19442423850747321215A2214900139DFA2186B456C843AF6ACC"
telegram = Base.decode16!(raw_telegram)
IO.puts "Encoded Telegram: #{raw_telegram}"
IO.puts "Encoded Telegram: #{inspect(telegram)}"
IO.puts "Encoded Telegram length: #{byte_size(telegram)}\n"

bloc1 = Telegram.get_bloc(telegram, 1)
bloc2 = Telegram.get_bloc(telegram, 2)
bloc3 = Telegram.get_bloc(telegram, 3)

<<key_h::size(32)>> = Base.decode16!("51728910")
<<key_l::size(32)>> = Base.decode16!("E66D83F8")

register = bloc1 ^^^ bloc2 ^^^ bloc3 ^^^ key_h ^^^ key_l

telegram_base = binary_part(telegram, 0, 15)
decoded_part = Telegram.decode(telegram, 15, byte_size(telegram), register)
result = telegram_base <> decoded_part

IO.puts "Decoded Telegram: #{Base.encode16(result)}"
IO.puts "Decoded Telegram: #{inspect(result)}"
IO.puts "Decoded Telegram length: #{byte_size(result)}"

telegram_direct.exs

# Added this for convenience of testing for multiple values
# Use Telegram.decode(telegram, key) for decoding.

defmodule Telegram do
  use Bitwise

  def decode(raw_telegram, raw_key) do
    telegram = raw_telegram |> String.upcase() |> Base.decode16!()
    bloc1 = get_bloc(telegram, 1)
    bloc2 = get_bloc(telegram, 2)
    bloc3 = get_bloc(telegram, 3)

    <<key_h::size(32)>> = get_key_segment(raw_key, 0)
    <<key_l::size(32)>> = get_key_segment(raw_key, 1)

    register = bloc1 ^^^ bloc2 ^^^ bloc3 ^^^ key_h ^^^ key_l

    telegram_base = binary_part(telegram, 0, 15)
    decoded_part = decode(telegram, 15, byte_size(telegram), register)
    Base.encode16(telegram_base <> decoded_part)
  end

  defp get_key_segment(key, segment_id) do
    key |> String.upcase() |> String.slice(segment_id * 8, 8) |> Base.decode16!()
  end

  defp get_bloc(telegram, bloc_nr) do
    <<bloc::size(32)>> = binary_part(telegram, 2 + (bloc_nr - 1) * 4, 4)
    bloc
  end

  defp get_byte(telegram, byte_nr) do
    <<byte::size(8)>> = binary_part(telegram, byte_nr, 1)
    byte
  end

  defp decode(telegram, byte, max_byte, register, out \\ <<>>)
  defp decode(_telegram, byte, max_byte, _register, out) when byte == max_byte, do: out
  defp decode(telegram, byte, max_byte, register, out) do
    {new_register, pout} = decode_single(0, 8, register, 0)
    new_byte = get_byte(telegram, byte) ^^^ pout
    decode(telegram, byte + 1, max_byte, new_register, out <> <<new_byte>>)
  end

  defp decode_single(count, max_count, register, pout) when count == max_count, do: {register, pout}
  defp decode_single(count, max_count, register, pout) do
    out = 0
    |> maybe_xor(register &&& 0x00000002)
    |> maybe_xor(register &&& 0x00000004)
    |> maybe_xor(register &&& 0x00000800)
    |> maybe_xor(register &&& 0x80000000)
    register = (register <<< 1) + out
    pout = (pout <<< 1) + out

    decode_single(count + 1, max_count, register, pout)
  end

  defp maybe_xor(input, condition) do
    if condition > 0, do: input ^^^ 1, else: input
  end
end

IO.puts Telegram.decode("19442423850747321215A2214900139DFA2186B456C843AF6ACC", "51728910E66D83F851728910E66D83F8")