An algorithm for encryption and decryption. A cipher replaces a piece of information (an element in plaintext) with another object, with the intent to conceal meaning. Typically, the replacement rule is governed by a secret key.

Ci"pher (?), n. [OF. cifre zero, F. Chiffre figure (cf. Sp.cifra, LL. cifra), fr. Ar. ssifrun, ssafrun, empty, cipher, zero, fr. ssafira to be empty. Cf. Zero.]

1. Arith.

A character [0] which, standing by itself, expresses nothing, but when placed at the right hand of a whole number, increases its value tenfold.

2.

One who, or that which, has no weight or influence.

Here he was a mere cipher. W. Irving.

3.

A character in general, as a figure or letter.

[Obs.]

This wisdom began to be written in ciphers and characters and letters bearing the forms of creatures. Sir W. Raleigh.

4.

A combination or interweaving of letters, as the initials of a name; a device; a monogram; as, a painter's cipher, an engraver's cipher, etc. The cut represents the initials N. W.

5.

A private alphabet, system of characters, or other mode of writing, contrived for the safe transmission of secrets; also, a writing in such characters.

His father . . . engaged him when he was very young to write all his letters to England in cipher. Bp. Burnet.

Cipher key, a key to assist in reading writings in cipher.

Ci"pher, a.

Of the nature of a cipher; of no weight or influence.

"Twelve cipher bishops."

Milton.

Ci"pher, v. i. [imp. & p. p. Ciphered (?); p. pr. & vb. n. Ciphering.]

To use figures in a mathematical process; to do sums in arithmetic.

"T was certain he could write and cipher too. Goldsmith.

Ci"pher, v. t.

1.

To write in occult characters.

His notes he ciphered with Greek characters. Hayward.

2.

To get by ciphering; as, to cipher out the answer.

3.

To decipher.

[Obs.]

Shak.

4.

To designate by characters.

[Obs.]

Shak.

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