Shows DES complementation property

mydes.erl

-module(mydes).


-export([test/0, complement/1]).

complement(<<>>) ->
    <<>>;
complement(<<1:1, Rest/bitstring>>) ->
    Complement = complement(Rest),
    <<0:1, Complement/bitstring>>;
complement(<<0:1, Rest/bitstring>>) ->
    Complement = complement(Rest),
    <<1:1, Complement/bitstring>>.

encrypt(Msg, Key) ->
    crypto:crypto_one_time(des_ecb, Key, Msg, true).

test() ->
    Message = <<"Some Message">>,
    Key = crypto:strong_rand_bytes(8),
    io:format("Cipher: ~p.~n", [complement(encrypt(Message, Key))]),
    io:format("Complement: ~p.~n", [encrypt(complement(Message), complement(Key))]).