Simon Singh writes wonderfully understandable books about complicated topics. This basic treatment of a history of codes, codebreaking and code breakers is at once both easy to understand and yet rich in nuance and explanation. It’s one of those great books with lots of extra appendices where you can go for more information but don’t need to be bored with it if you don’t. Singh is also British so this exposition talks a lot about the simultaneous work going on in code creation and breaking in the UK as well as in the US. Apparently, public key cryptography, according to recently declassified information, was created by British intelligence at about the same time as it was discovered in the US, but national security kept the Brits' discovery under wraps until just recently. This book is full of little tidbits like that, codes cracked, problems created and solved and the obsessed and single minded folks who make codes their lives.