CYPHER, or CIPIIER. To write in cypher denotes the art of communicat ing by writing in such a manner, as shall be legible only to those who are acquaint ed with the rules by which the charac ters made use of are formed or disposed. It is principally used in diplomatic cor respondence, or on other national affairs, such as those relating to the operations of war. As the nature of alphabetic writ ing, and the structure of languages, ne cessarily imply certain indispensable ha bitudes of the letters and words, it often happens that the laws or conditions made use of for the sake of secrecy can be de tected by skilful persons, and the secret by that means discovered. The art of iSliscovering the sense of writings of the description here mentioned is called de cyphennz.
One of the most obvious methods of disguising the alphabet will consist in changing the characters. Thus, for ex ample, if the English language were writ ten in Greek characters, it would not be legible by a person unacquainted with them ; or if the English alphabet were to be transposed, as by taking every conse quent letter for its antecedent, namely, for a, c for 5, d for c, &e. ; or by any other ruleofarrangement, thesam e consequence would follow, and the writing would be secret, unless the sagacity of the reader should enable him to des-elope the condi tions; which in the cases here mentioned it would not be difficult to do.
From the comparative facility of decy phering writings made in a disguised sin gle alphabet, it became necessary to use contrivances of less simplicity. By sub stituting figures in the place of letters, and by using more than one figure to denote each letter ; and, in addition to this, by adopting a considerable number of dis tinct characters, letters, or combinations of figures, for each letter of the alpha bet, the difficulty of decyphering may be prodigiously augmented. Thus, for ex ample, if a table were made consisting of twenty-four vertical columns, having a letter of the alphabet at the head of each ; • and six distinct ranges of characters were placed on horizontal lines beneath ; and, in particular, if a greater number of cha racters were allowed for the vowels, in proportion to their frequency of recur rence ; and if, in writing, each range be used in succession ; the developement of a Communication thus made would he ex tremely difficult. Or, otherwise, if a square of twenty-five compartments be made resembling the multiplication table, but containing the letters of the alphabet, and the first five digits be placed over the top row and down the side, each letter may be denoted by the two figures which stand opposite the same, namely, at the top and the side, as in the table beneath.
In this manner, the letter a will be de noted by 11, and the letter 6 by 12,, the letter n by 34, and the letter w by 52, tcc. ; and as it is advantageous, in every kind of cypher, that the words should not be written from each other, or with spaces between, but that every line should be continuous throughout, the other digits, namely, 67890, may be used to denote blank spaces. It is manifest also, that if there were four or five of these tables, each containing the alphabet in a differ ent order of arrangement, and the several lines of the intended communication were to be written, in succession, according to each of the tables respectively, the task of decyphering would be greatly en In fact it does not appear difficult to contrive a multiplicity of cyphers, which shall be beyond the reach of human skill to develope, otherwise than by some for tuitous circumstance or happy observa tion, not dependant upon rule ; but at the same time it must be observed, that most of those cyphers which are the most difficult to discover are also te dious, and not unfrequently difficult in the use.
For the sake of brevity we pass over the variety of arbitrary marks, which may be substituted for the letters of the alpha bet, or for entire words ; such as a single dot or right line, or unvaried character, deriving its distinct significance from its several positions with regard to ruled fines or spaces on the paper ; which lines may either be actually drawn or apparent, or else their places may be indicated by dots or other marks, to enable the reader himself to draw them. Writing, by means of the characters of music, comes under this class ; and the telegraphic signals now so generally adopted may be refer red to those arbitrary combinations of dots which signify letters or words. And when the notion of these combinations has once been clearly apprehended, it will be easy to deduce the methods of com municating intelligence by combinations, either contemporaneous or successive, of torches, fires, rockets, or the sounds of bells, trnmpets, cannon, and other suit able instruments.