Codes and Ciphers. Julius Caesar, the Enigma and the internet

This is a popular introduction to the basic concepts and methods of cryptology, the science and art of secret communication.
The first seven chapters are concerned with classical cryptography and cryptoanalysis, starting with simple substitution and polyalphabetic ciphers such as the Vigenère cipher and various transposition ciphers. Examples of monograph to digraph substitutions, digraph to digraph substitutions, and their combinations are presented. Each historical chapter starts with the description of a cipher and then presents detailed examples of its cryptoanalysis: important events in the history of cryptoanalysis (breaking the Zimmermann telegram in World War I, solution of the Enigma cipher of the Germans in World War II) are also described. Another chapter is concerned with the description and cryptoanalysis of one of the Hagelin machines. Three chapters deal with modern cryptography: one explains random and pseudorandom sequences of numbers and letters and how to produce them; another explains the basic concepts and ideas of public key cryptography, including the Diffie-Hellman key exchange system; the last chapter is on security of internet communications, explaining DES and its implementation, authentication and signature verification.
The book is written in a lively and amusing style but not at the expense of mathematical rigour. It contains 28 mathematical appendices, where mathematical concepts used in the text are explained in more detail.

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