Book excerpt: Cryptography, secret writing, is enjoying a scientific renaissance following the seminal discovery in 1977 of public-key cryptography and applications in computers and communications. This book gives a broad overview of public-key cryptography - its essence and advantages, various public-key cryptosystems, and protocols - as well as a comprehensive introduction to classical cryptography and cryptoanalysis. The second edition has been revised and enlarged especially in its treatment of cryptographic protocols. From a review of the first edition: "This is a comprehensive review ... there can be no doubt that this will be accepted as a standard text. At the same time, it is clearly and entertainingly written ... and can certainly stand alone." Alex M. Andrew, Kybernetes, March 1992