Gaines - Cryptanalysis ; a study of ciphers and their solution

A STUDY OF CIPHERS AND THEIR SOLUTION

(formerly published under the title ELEMENTARY CRYPTANALYSIS)

HELEN FOUCH GAINES

DOVER PUBLICATIONS, INC. NEW YORK

Copyright 1939 by
American Photographic Publishing Co.
First Printing November 1939
Second Printing February 1941
Third Printing April 1942
Fourth Printing January 1943
Fifth Printing January 1944
Copyright , 1956, by Dover Publications, Inc.

All rights reserved.

This new Dover edition, first published in 1956, is an unabridged and corrected edition of the book originally published under the title ELEMENTARY CRYPTANALYSIS. It is augmented for the first time with solutions to all cryptograms prepared by Max Katz and Geoffrey Mott-Smith.

Library of Congress Catalog Card Number: 57-203

International Standard Book Number
eISBN-13: 978-0-486-80059-2

Manufactured in the United States by Courier Corporation
20097326 2014
www.doverpublications.com

AFFECTIONATELY DEDICATED
TO THE MEMORY OF

GEORGE C. LAMB (DAMONOMAD)

THROUGH WHOSE UNSELFISH ENDEAVOR
THIS VOLUME HAS BEEN MADE AVAILABLE TO
THE CRYPTOGRAPHIC STUDENTS OF THE WORLD.

AND TO THE MEMORY OF

HELEN FOUCH GAINES

PREFACE

The word cryptography, properly speaking, embraces the entire field of secret writing, while that branch of the subject dealing with the solution and reading of cryptic messages is generally referred to as cryptanalysis.

Works on the subject of secret writing are comparatively numerous, if not always easily available, but works devoted purely to the analysis of such writing and the solving of its cryptograms have, until recently, been so rare as to be almost non-existent for the general reader.

Today we have two particularly excellent works, but both in foreign languages: Cours de cryptographie, by General Marcel Givierge, and Manuale di crittografia, by General Luigi Sacco. In English, we find a more elementary work, The Solution of Codes and Ciphers, by Louis C. S. Mansfield (Maclehose, London), which, the writer has been told, is to be a first volume. As to Americas contribution, we seem to find only small books such as Colonel Parker Hitts A B C of Secret Writing, covering three ciphers, or Colonel H. O. Yardleys Yardleygrams.

There are, however, many works which deal most interestingly with the analysis and decryptment of some one particular cipher. Most of these are short works, published in magazines or incorporated into books of a general nature, and nearly always the one cipher dealt with is that type of simple substitution which appears with separated words in the puzzle sections of our current magazines and newspapers.

One well-known gem of cryptanalysis, equal to any modern specimen, can be found in the story, The Gold Bug, by Edgar Allan Poe. This, too, deals with the simple substitution cipher just referred to, but covers a case in which word-divisions are absent. Poe has also left us an essay called Cryptography.

Rosario Candelas recent book, The Military Cipher of Commandant Bazeries, shows the unraveling of one particular cryptogram which, for many years, had baffled the best efforts of all amateurs, and, it is rather suspected, of some few who were not amateurs. The book contains a chapter on general cryptanalysis, and also some cryptograms for solution.

Secret and Urgent, by Fletcher Pratt, is primarily a history of secret writing (a most interesting one, by the way), but contains also a number of examples of cryptanalysis; it also shows a table which the writer has never before seen in published form: a list of English trigrams (three-letter sequences) and the frequency with which they are used in the language. Other examples of decryptment may be found in the Macbeth translation of Langies genial little book, De la cryptographie; the appendix to this translation contains the coveted Playfair demonstration, prepared by Lieutenant Commander W. W. Smith of the United States Navy.

Just why so absorbing a subject has been so neglected in a world full of puzzle lovers is hard to understand, especially since the analytic writer, in addition to entertainment, has something to offer of a more serious nature. It is true that trained cryptanalysts are not greatly in demand in peacetime, and that our present corps of cryptographers has a personnel more than ample for providing necessary codes and ciphers, scientifically selected to fit their individual purposes, and safeguarded with suitable protective devices. Yet of what value is the most excellent of ciphers if, at the time of direst need, this cipher, with all of its safeguards, must be placed in the hands of even one man who cannot appreciate its intrinsic value or imagine a need for extra precautions? At any rate, we make our feeble attempt to reach this one man. May he learn, at least, that there are reasons for his instructions!

In the planning of the present treatise, all purely historical aspects of secret writing were neglected, and many well-known ciphers whose interest is chiefly historical or literary have either been omitted or given but cursory treatment. Certain other ciphers, representative of types, have been treated at whatever length seemed advisable for bringing out principles; and, with each type discussed, a generous number of cryptograms has been provided, on which the student will be able to test his skill as he learns. The student who masters these fundamentals will be acquainted with the principal forms of cipher, and will be able to solve cryptograms prepared by means of these ciphers provided the cryptograms are of adequate length and based on a language which he understands, or of which he is able to secure understandable specimens. Within limits, he should also be able to analyze and solve such cryptograms without being told in advance what the cipher is. This, we believe, is the kind of text-book desired by the many who desire information about ciphers.

Its material, compiled by members of the American Cryptogram Association, has had to be gathered from a great many sources, both within the organization and elsewhere, making it impossible, at times, to give credit where credit is due. Our chief indebtedness, however, is to M. E. Ohaver for a series of articles published during the years 1924 to 1928 in the former Flynns Magazine and most unfortunately no longer obtainable from the publishers. Further acknowledgment should be made to Colonel Parker Hitt, whose Manual for the Solution of Military Ciphers, though not available for general distribution, can usually be consulted in large public libraries. We have also borrowed liberally from foreign sources, and members of the association have most generously contributed the results of their original research. For this collaboration and co-operation, the writer is particularly grateful.

The subject which we are about to study is the analysis and solution of cipher, though not including code, which is a very special form of cipher demanding something more than elementary knowledge; nor shall we enter at all into the subject of invisible inks, certainly a most important aspect of secret writing, but belonging to the province of chemistry rather than to that of cryptanalysis. Cipher machines, also, are not within our present scope.

The term cipher implies a method, or system, of secret writing which, generally speaking, is unlimited in scope; it should be possible, using any one given cipher, to transform any plain text whatever, regardless of its length and the language in which it is written, into a cryptogram, or single enciphered message. The process of accomplishing this transformation is called