As a young mathematician, I learned how to make and break simple codes from Sinkov's beguiling introduction to cryptanalysis. In the intervening forty years there has been a revolution in cryptography, and it is fitting that for a modern edition of Sinkov's classic, Todd Feil has indicated the nature of this revolution by adding a lucid introduction to RSA public-key encryption and the number theory which underlies it. If you know a young code breaker who might become a young mathematician, buy her or him this book! Or buy it for yourself and try decoding those messages.

Sinkov's Elementary Cryptanalysis is an eminently readable classic that introduces the reader to both the techniques and the spirit of cryptanalysis -- the art and science of reading secret messages. Todd Feil has done a fine job of modernizing the language of the original. His chapters on RSA encryption and one-time pads give added value to the original, especially the very nice treatment of RSA that assumes almost no prior knowledge of number theory.