<a href="http:&#x2F;&#x2F;www.amazon.com&#x2F;The-Codebreakers-Comprehensive-Communication-Internet&#x2F;dp&#x2F;0684831309" rel="nofollow">http:&#x2F;&#x2F;www.amazon.com&#x2F;The-Codebreakers-Comprehensive-Communi...</a><p>A good read about the crypto behind the Enigmia and other encryption approaches. A fun read.