[zandor]

This book is really worth getting if you can find it somewhere for a fair price. It's almost worth it for the appendix alone where Marian Rejewski himself describes how they broke the original Enigma code.

http://www.amazon.com/Enigma-German-Machine-Foreign-intellig...

[adaszko]

Thanks for pointing it out. Can one find some mathematics behind Enigma in it?