Cryptanalysis ; a study of ciphers and their solution

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Cryptanalysis: A Study of Ciphers and Their Solution

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Cryptanalysis : a study of ciphers and their solution / Helen FoucheĢ Gaines - Details - Trove

This does also classifies them into the historic context - a good idea. Besides that, the content is nothing new. Mentionable is the fact, that in the first edition includes "a cryptogram upon the reader is invited to test his skills.

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Lots of amateur and pro-Cryptographs have tried their luck and there were many different solution methods were found Cryptogram , and Cryptologia The practice cryptogram was removed from the second edition - see pictures. The cryptogram is one of the few, old and unsolved non-military cryptograms that are no hoax and are solvable.

Cryptanalysis - a study of ciphers and their solution.

Vernam Cipher (One time pad) --Transposition Technique -- Encryption and Decryption

This is the unchanged paperback edition - and therefor without the congeniality of the original version. The only changes that I saw is the changed title and the dedication - besides George C. Lamb it is now appended with "To the memory of Helen Fouche Gaines". Still probably the best book that describes all manual en- and decipher methods. Elementary cryptanalysis - a study of ciphers and their solution. A fantastic book - or better schoolbook.

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With lots of examples and practices of all known ciphers. This is the third edition of the published book. These substitutes may be groups of letters, or groups of digits, or actual words selected from ordinary language. Very common words or expressions are usually provided with more than one substitute; and nearly always there are substitutes provided for syllables 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 decoding , and the vocabulary terms would be in mixed order. Just what is meant can be seen in Fig. 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 necessary 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 conditions 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 Department, 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 communication, 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.

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Moreover, it is conceded that a meaningless text will not be transmitted with absolute accuracy, and a cryptogram which is to be sent by this means must not be of such a nature that ordinary errors of transmission will render it unintelligible at the receiving office. 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 forever 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.

As to just what constitutes the "perfect" cipher, perhaps it might be said that this description fits any cipher whatever which provides the degree of security wanted for an individual purpose, and which is suited in other respects to that individual purpose. 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 numerous other factors including espionage , it is conceded by the various War Departments 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 machine.

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.

A. Adrian Albert

The ideal cipher, under these conditions, would be one which is simple in operation, preferably requiring no written memoranda or apparatus which cannot be quickly destroyed and reconstructed from memory, and having a key which is readily changed, easily communicated, and easily remembered. 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.