CIPHER, or Cypher, one of the Arabic characters or figures used in computation.

Cipher is also a kind of enigmatic character composed of several letters interwoven, which are generally the initial letters of the person’s names for whom the ciphers are intended. These are frequently used on seals, coaches, and other movables. Anciently, merchants and tradesmen were not allowed to bear arms; but in lieu thereof, they bore their ciphers, or the initial letters of their names, artfully interwoven about a cross, of which we find divers instances on tombs, and other monuments.

Cipher likewise denotes certain secret characters, disguised and varied, used in writing letters containing some secret, and not to be understood except by those between whom the cipher is agreed on.

De la Guilletière, in his Lacedaemon Ancient and Modern, endeavours to make the ancient Spartans the inventors of the art of writing in cipher. Their scytala, according to him, was the first sketch of this mysterious art. The scytalae were two rollers of wood, of equal length and thickness; one of which was kept by the ephori, the other by the general of the army sent on any expedition against the enemy. Whenever those magistrates meant to send any secret orders to the general, they took a slip of parchment and rolled it close round the scytala which they had reserved, and in this state wrote their instructions, which appeared perfect and consistent while the parchment continued on the roll; but when taken off, the writing was maimed, and without connection, though it was easily retrieved by the general upon his applying it to the scytala in his possession. Polybius says that Aeneas Tacitus had collected together twenty different manners of writing, so as not to be understood by any but those in the secret; and that part were invented by himself, and part used before his time. Trithemius, Baptista Porta, Vigenère, and P. Niceron, have written expressly on the subject of ciphers.

As the writing in cipher has become an art, so the reading or unravelling thereof is called deciphering. The rules of deciphering are different in different languages. By observing the following, any one may read a common cipher written in English.

1. Observe the letters or characters that most frequently occur, and set them down for the six vowels, including y; and of these the most frequent will generally be e, and the least frequent u.

2. The vowels that most frequently come together are ea and ou.

3. The consonant most common at the end of words is s, and the next frequent is r or t.

4. When two similar characters come together, they are most likely to be the consonants f, l, or s, or the vowels e or o.

5. The letter that precedes or follows two similar characters is either a vowel, or l, m, n, or r.

6. In deciphering, begin with the words that consist, of a single letter, which will be either, a, I, o, or &p

7. Then take the words of two letters, one of which will be a vowel. Of these words the most frequent are, an, to, be, by, of, on, or, no, so, as, at, if, in, is, it, he, me, my, us, we, am.

8. In words of three letters there are most commonly two consonants. Of these words the most frequent are, the, and, not, but, yet, for, thd, how, why, all, you, she, his, her, our, who, may, can, did, was, are, has, had, let, one, two, six, ten, &c. Some of these, and words of two letters, will be found in every sentence.

9. The most common words of four letters are, this, that, then, thus, with, when, from, here, some, most, none, they, them, whom., mine, your, self, must, will, have, been, were, four, five, nine, &c.

10. The most usual words of five letters are, their, these, those, which, where, while, since, there, shall, might, could, would, ought, three, seven, eight, &c.

11. Words of two or more syllables frequently begin with double consonants, or with a preposition; that is, a vowel joined with one or more consonants. The most common double consonants are, bl, br, dr,fl,fr, gh, gr, ph, pl, pr, sh, sb, sp, st, th, tr, wh, wr, &c.; and the most common prepositions are, com, con, de, dis, ex, im, in, int, mis, per, pre, pro, re, sub, sup, un, &c.

12. The double consonants most frequent at the end of long words are, ch, ld, lf, mn, nd, ng, rl, rm, rn, rp, rt, sm, st, xt, &c.; and the most common terminations are, ed, en, er, es, et, ing, ly, son, sion, tion, able, ence, ent, ment, full, less, ness, &c.

By applying these rules, any common cipher written in English maybe deciphered; and, mutatis mutandis, a cipher written in any language may be evolved by an application of the principle on which these rules are constructed.