Is this the one you are talking about
:
http://users.telenet.be/d.rijmenants/en/enigmasim.htm
I have included a number of coded messages in my game but only for the purely visual immersiveness, there is no way in-game to decode them. tThis is a real pity as it would have added hugely if you received specific coded messages which had to be decrypted and were revelent to your mission.