This banner text can have markup. Search the history of over billion web pages on the Internet. All rights reserved under Pan American and international copyright conventions. This new Dover edition, first published in Works on the subject of secret writing are comparatively numerous, if not al- ways 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.

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This banner text can have markup. Search the history of over billion web pages on the Internet. All rights reserved under Pan American and international copyright conventions. This new Dover edition, first published in Works on the subject of secret writing are comparatively numerous, if not al- ways 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 cryptographic, by General Marcel Givierge, and Manuale di crittografia, by General Luigi Sacco. Mansfield Maclehose, London , which, the writer has been told, is to be a first volume.

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 news- papers.

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. The book contains a chapter on general cryptanalysis, and also some cryptograms for solution.

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 en- tertainment, 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 vi PREFACE a need for extra precautions? Cer- tain other ciphers, representative of types, have been treated at whatever length seemed advisable for bringing out principles; and, with each type discussed, a gen- erous 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. Our chief indebtedness, however, is to M. 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 particu- larly grateful. General Information. Concealment Devices III. Transposition Types IV. Substitution Types IX. Simple Substitution — Fundamentals X. Lamb XI. Fraprie SOLUTIONS INDEX CHAPTER I General Information 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 some- thing 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, gener- ally speaking, is unlimited in scope; it should be possible, using any one given cipher, to transform cany plain text whatever, regardless of its length and the lan- guage in which it is written, into a cryptogram, or single enciphered message.

The process of accomplishing this transformation is called encipherment ; the opposite process, that of transforming the cryptogram into a plaintext, is called decipher- ment. The word decrypt, with its various derivatives, is being used here to signify the process of solving and reading cryptograms without any previous knowledge as to their keys, or secret formulas; thus the word decipher has been left to convey only its one meaning, as mentioned above: the mechanical process of applying a known key.

Our word decrypt, however, is an innovation borrowed from the modern French and Italian writers, and is somewhat frowned upon by leading cryptologists. The word digram is being used to indicate a two-letter sequence; similarly, we have trigrams, tetragrams, pentagrams, etc.

Concealment Cipher 2. Transposition Cipher 3. In concealment cipher, the true letters of the secret message are hidden, or dis- guised, by any device whatever; and this type of cipher, as a general rule, is in- tended to pass without being suspected as the conveyor of a secret communication. In transposition cipher, the true letters of the secret message are taken out of their text-order, and are rearranged according to any pattern, or key, agreed upon by the correspondents.

In substitution cipher, these original text-letters are replaced with substitutes, or cipher-symbols, and these symbols are arranged in the same order as their originals.

There may, of course, be combinations of types, or combinations of sev- eral forms belonging to a single type. The aristocrat of the cipher family is code. This is a form of the substitution cipher which requires the preparation, in advance, of a code book. These sub- 3. Very common words or expressions are usually provided with more than one substitute; and nearly always there are substitutes provided for syl- lables and single letters, so as to take care of all words not originally included in the vocabulary.

No code presents any real, security unless the code symbols have been assigned in a thoroughly haphazard manner.

This means that any really good code would have to be printed in two separate sections. In one of these, the vocabulary terms would be arranged in alphabetical order, so that they could be readily found when enciphering encoding messages; but the code groups would be in mixed order and hard to find. In the other section, the code groups would be rearranged in straight alphabetical or numerical order, so as to be readily found when deciphering de- coding , and the vocabulary terms would be in mixed order.

Just what is meant can be seen in Fig. Polyphones are symbols which may have more than one meaning. The terms encoding , decoding are usually preferred to enciphering , d eciphering.

A code of this kind, with symbols assigned absolutely at random , provided it is carefully used never without re-encipherment and a close guard kept over the code books, represents perhaps the maximum of security to be attained in cryptographic correspondence; and security, of course, is of prime importance in the selection of a cipher for any practical purpose.

But in considering the relative merits of the various ciphers, it is always neces- sary to take into account many factors other than security, each cipher being evaluated in connection with the purpose for which it is wanted: Under what con- ditions must the encipherment and decipherment take place? How must the cryptograms be transmitted? How much of the enciphered correspondence is likely to be intercepted? What degree of security, after all, is absolutely imperative?

A commercial, or other, firm, having a permanent base of operations, and in little danger of being blown to bits by an enemy shell, would not consider the first of these questions from the same angle as the War Department; and the War De- partment, though considering all of them from several different angles of its own, would still not consider them from the same viewpoint as the State Department. If messages are to be sent by mail, or by hand, or by telephone, or pasted on a billboard, it is conceivable that a cipher which doubles or trebles their length could still be a practical cipher.

For transmission by telephone, the presumption is that the cryptogram must be pronounceable, or, certainly, audible. For written, com- munication, individual purposes have been served by means of pictures. But when the cryptograms are to be sent by wire or radio, it must be possible to convert them into Morse symbols, either letters or figures, but not intermingled letters and figures.

Here, length must be considered, involving questions of time, expense, and the current telegraphic regulations. A factor of particularly grave importance in the selection of a cipher to fit a given purpose is the probable amount of enciphered material which is going to fall into the possession of unauthorized persons.

A criminal, who has had to send but one brief cryptogram in a lifetime, might reasonably expect that it will remain for- ever unread, no matter how weak the cipher. A commercial firm, transmitting thousands of words over the air, is more vulnerable; and the diplomatic office, or the newspaper office, which makes the mistake of publishing almost verbatim the translations of cryptograms which have been transmitted by radio, and thus has surely furnished the cipher expert with a cryptogram and its translation , might just as well have presented him with a copy of its code book.

Even a basically weak cipher, in the hands of an expert, can be made to serve its purpose; and the strongest can be made useless when improperly used. In the present text, we are likely to be found looking at ciphers largely from a military angle, which, apparently, has a more general interest than any other.

In time of war, the cryptographic service, that is, the encipherment and transmitting service, is suddenly expanded to include a large number of new men, many of whom know nothing whatever of cryptanalysis , or the science of decryptment. Many of these are criminally careless through ignorance, so that, entirely aside from numer- ous other factors including espionage , it is conceded by the various War Depart- ments that no matter what system or apparatus is selected for cipher purposes, the enemy, soon after the beginning of operations, will be in full possession of details concerning this system, and will have secured a duplicate of any apparatus or ma- chine.

For that reason, the secrecy of messages must depend upon a changeable key added to a sound basic cipher. Speed in encipherment and decipherment is desirable, and often urgent; and the conditions under which these operations must often take place are conducive to a maximum of error. The ideal cipher, under these conditions, would be one which is simple in operation, preferably requiring no written memoranda or ap- paratus which cannot be quickly destroyed and reconstructed from memory, and having a key which is readily changed, easily communicated, and easily remem- bered.

Yet the present tendency, in all armies, seems to be toward the use of small changeable codes , which are written printed documents; and, for certain purposes, small mechanical devices. An enormous number of military cryptograms will be transmitted by radio and taken down by enemy listeners, and even the ordinary wire will be tapped. It is expected that the enemy will intercept dozens, and even hundreds, of cryptograms in a single day, some of which will inevitably be enciphered with the same key.

With so much material, knowing the general subject matter, and often exactly what words to expect, or the personal expressions invariably used by individuals, it is conceded that he will read the messages.

All that is desired of a cryptogram is that it will resist his efforts for a sufficient length of time to render its contents value- less when he finally discovers them. By that time, of course, the key w T ill have been changed, probably several times, and even the cipher. With these general facts understood, we may first dispose hastily of the con- cealment cipher, after which we will examine at greater length the two legitimate types, the transpositions and the substitutions.

Perhaps its oldest known ap- plication is found in the ancient device of writing a secret message on the shaved head of a slave and dispatching the slave with his communication after his grow- ing hair had covered the writing. Or, if this appears a little incredible, the an- cients have left us records of another device considerably more practical: that of writing the secret message on a wooden tablet, covering this with a wax coating, and writing a second message on top of the first.

In the middle ages we meet a development called puncture cipher; any piece of printed matter, such as a public proclamation, serves as the vehicle, and the cipher consists simply in punching holes with a pin under certain letters, so that these letters, read in regular order, will convey the desired information.

It is said that this kind of concealment writing was resorted to in Engfand at a compara- tively recent period, to avoid the payment of postage. Postage on letters was very high, while newspapers were permitted to travel free, and the correspondents sent their messages very handily by punching holes under the letters printed in newspapers.

Where the sender of a. But concealment cipher is not necessarily confined to written and printed matter. Again, w'e hear of cases in which the arrangement of stamps on envelopes is made to represent the terms of a miniature code. All such devices are, of course, combina- tion-cipher rather than pure concealment, since the stones, candies, and so on, must first be made the substitutes for letters or code terms. A method of pure concealment, said to have been used by Cardinal Richelieu, involved the use of a grille.

Grilles are made of cardboard, sheet-metal, or other fiat material, and are perforated with any desired number, size, and arrangement of openings. The Richelieu grille, of approximately the same size and shape as the paper used for correspondence, could be laid over a sheet of paper so as to reveal only certain portions, and the secret message was written on these. The grille was then removed and the rest of the sheet was filled in with extraneous matter in such a way as to present a seemingly continuous text.

The legitimate recipient of this message, having a duplicate grille, simply laid this grille over the sheet of paper, and read his message through the apertures. Concealment cipher goes by various names, as null cipher , open-letter cipher, conventional writing, dissimulated writing , and so on.

In this, casual words have special meanings. Believe antenna connected improperly, but do what- ever you can.


Helen Fouché Gaines

The book described the principal cryptographic systems of the 19th century and cracking methods including elementary contact analysis cryptanalysis. Shortly after the publication of the book, she died. From Wikipedia, the free encyclopedia. This article has multiple issues. Please help improve it or discuss these issues on the talk page.


Cryptanalysis: A Study of Ciphers and Their Solution


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