General Report on Tunny

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                    01   PREFACE    (SHOULD BE READ)

The 'General Report on Tunny' is an account of machine and statistical methods for breaking Tunny ciphers. Language methods are briefly described so that the report may be understood without previous knowledge. For a fuller account of language methods the reader should consult the report of Major Tester's Section.

This report is essentially cryptographic and is complementary to the electrical report prepared by Mr. Flowers. Most of the book concerns cryptographic methods in their prime, but there is also a little historical perspective. The plan of the book is as follows:

Part 1 gives a broad outline of the entire subject. This part should be well understood by the reader before he proceeds to the other parts which may then be read in any order.

In Part 2 all methods are described in some detail. The later section (W, X, Y, Z) of each chapter covers advanced theoretical aspects and involve a knowledge of mathematics of at least sixth form standard. These sections may be omitted on a first reading, but give valuable general examples of statistical cryptographic methods.

A description of the other parts is given in the table of contents. It is hoped that the 'Conclusions' may be of value in other sections of the Foreign Office.

The report contains a number of references to the Research Logs of Mr. Newman's Section, (labelled R0, R1, R2, R3, R4, R5) and that of Major Tester's Section (labelled R41). Those references which are not preceded by the word 'see' are intended to be of purely historical interest. The correlation of reference with date is given by the following list:

R0    p 1    15th August, 1943
      26    September
      59    October
      92    November
R1     13    December
      34    January, 1944
      78    February
R2      5    March
      37    April
      60    May
      90    June
R3      5    July
      38    August
      62    September
      83    October
     106    November
R4     35    December
      77    January, 1945
R5     1    February
      33    March
     73    April
     111    May

References to the report itself are of the form 36F(b) which means Part 3, Chapter 6, Section F, Paragraph (b). Formulae are numbered in Arabic numerals by sections (e.g. (26F4) for the 4th formula of Part 2, Chapter 6, Section F), and tables and exhibits are numbered in Roman numerals by chapters (e.g. 26(II)). Section headings are listed at the beginning of each chapter.

The authors wish to thank all who have helped them with the report, and in particular to acknowledge the help they have received from the reports of the Research Section, Major Tester's Section and Sixta which have in many places been quoted verbatim and without further acknowledgement.

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