"The best single book on cryptology today." -- Cryptologia (from a review of a previous edition) From the reviews of the fourth edition: "This comprehensive updated edition is divided into two sections. The first part of the book deals with The People and the second concentrates on The Machinery. ... This volume includes 191 Figures, 29 Tables and 16 Color Plates, plus an Appendix. ... Friedrich L. Bauer Professor Emeritus of Mathematics and Computer Science ... has written an outstanding book on cryptology that belongs in your personal library or as a gift for a friend. ... There are other fascinating sidelights to this excellent book." (The Cryptogram, Page 15, 2007) "By far the best single work on the subject." -- David Kahn "It contains a wealth of material on the history of classical cryptology, focusing especially on the first half of the 20th century. ... The book is so thorough that it could serve as a textbook for those who want to develop their skills in this area. ... this book is an excellent source for the history of codemaking and codebreaking in the early and mid-20th century." (Neal Koblitz, SIAM Review, Vol. 52 (4), 2010)