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ELEMENTARY CRYPTANALYSIS
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.
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 plaintext 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 encipherment; the opposite process, that of transforming the cryptogram into a plaintext, is called decipherment.
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 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., to indicate sequences of three, four, five, etc. letters.
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.
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 plaintext 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 encipherment; the opposite process, that of transforming the cryptogram into a plaintext, is called decipherment.
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 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., to indicate sequences of three, four, five, etc. letters.
407 pages, Kindle Edition
Published January 14, 2025
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