This detailed technical account of breaking Tunny is an edition of a report written in 1945, with extensive modern commentary This detailed technical account of breaking Tunny is an edition of a report written in 1945, with extensive modern commentary Breaking Teleprinter Ciphers at Bletchley Park gives the full text of the General Report on Tunny (GRT) of 1945, making clear how the ideas, notation and the specially designed machines that were used differ from what was generally accepted in 1945, and, where a modern reader might be misled, from what is understood now. The editors of this book clarify the sometimes slightly strange language of the GRT and explain the text within a variety of contexts in several separate historical story lines, some only implicit in the GRT itself. The first story, told by the authors of the GRT, describes how, using specially designed machines, including from 1944 the "Colossus", the British broke the enciphered teleprinter messages sent by the highest command levels of the Germany Army. The cipher machines the Germans used were the Lorenz SZ 40 series, called "Tunny" by the British. The second story shows how the use of then-unfashionable Bayesian methods in statistics proved to be essential to the British success. The third story describes a significant stage in the invention of the modern digital computer. This story is connected with Alan Turing's 1936 paper on the theory of computability, which is nowadays seen as a starting point for the development of the modern digital computer. This book includes: Over 200 pages of commentary, biographies, glossaries, and essays related to the text of the General Report on Tunny The complete text of the original GRT, covering the general theory of Tunny breaking and of numerous refinements appropriate to special-case situations All the examples of original worksheets and printouts, showing the Tunny-breaking process in action, that appear in the GRT The main purpose of this book is to present the actual words of the GRT for use by readers with a serious interest in the history of cryptography, computing, or mathematics.

James A. Reeds is an applied mathematician and is currently on the research staff at the Center for Communications Research, Princeton, NJ. Whitfield Diffie is best known for his 1975 discovery of the concept of public key cryptography. Since 1993, he has worked largely on public policy aspects of cryptography. His position in opposition to limitations on the business and personal use of cryptography has been the subject of articles in the New York Times and programs on networks such as CNN. J.V. Field, an Honorary Visiting Research Fellow in the Department of History of Art at Birkbeck, University of London, is now a historian of science but in the 1960s worked as a computer programmer.