The German Enigma Cipher Machine: Beginnings, Success, and Ultimate Failure is the definitive tome on the Enigma. 

In the world of information systems, software technologies are frequently obsolete within a decade, and hardware in less time than that. So a book about an 80-year-old cryptographic device would seem to be as useful as a maintenance guide for a Model T. There is much to learn in this fascinating account, however. 

The German Enigma Cipher Machine is the story of one of the most notable pieces of security hardware ever made, an encoding device that looked like a small typewriter. The Germans used it, primarily during World War II, to send confidential communications. In their hubris, the Germans believed that the Enigma was utterly unbreakable and refused to believe otherwise even when their communiqués were being compromised. The Allied Powers were able to break the code after they acquired an Enigma machine and brought together a team of analysts from diverse countries to tease out its secrets. 

That's the basic story. This book is a collection of various articles from a cryptology journal called Cryptologia. Chapters are written by those who created the Enigma, worked to crack it, or studied it afterwards. Though many of the chapters are highly technical, the book still has enough valuable information for readers without a deep background in encryption. 

While the Enigma is dead and buried, the problems that doomed it-poor physical security, user error, and overreliance on the technology-are still relevant today. The Model T inventor's statement that "History is more or less bunk" to the contrary, Enigma provides lasting lessons.