Cipher

In cryptography, a cipher (or cypher) is an algorithm for performing encryption or decryption—a series of well-defined steps that can be followed as a procedure. An alternative, less common term is encipherment. To encipher or encode is to convert information from plain text into code or cipher. In non-technical usage, a "cipher" is the same thing as a "code"; however, the concepts are distinct in cryptography. In classical cryptography, ciphers were distinguished from codes. Codes operated by substituting according to a large codebook which linked a random string of characters or numbers to a word or phrase. For example, "UQJHSE" could be the code for "Proceed to the following coordinates". When using a cipher the original information is known as plaintext, and the encrypted form as ciphertext. The ciphertext message contains all the information of the plaintext message, but is not in a format readable by a human or computer without the proper mechanism to decrypt it.

The operation of a cipher usually depends on a piece of auxiliary information, called a key (or, in traditional NSA parlance, a cryptovariable). The encrypting procedure is varied depending on the key, which changes the detailed operation of the algorithm. A key must be selected before using a cipher to encrypt a message. Without knowledge of the key, it should be difficult, if not nearly impossible, to decrypt the resulting ciphertext into readable plaintext.

Most modern ciphers can be categorized in several ways

  • By whether they work on blocks of symbols usually of a fixed size (block ciphers), or on a continuous stream of symbols (stream ciphers).
  • By whether the same key is used for both encryption and decryption (symmetric key algorithms), or if a different key is used for each (asymmetric key algorithms). If the algorithm is symmetric, the key must be known to the recipient and sender and to no one else. If the algorithm is an asymmetric one, the enciphering key is different from, but closely related to, the deciphering key. If one key cannot be deduced from the other, the asymmetric key algorithm has the public/private key property and one of the keys may be made public without loss of confidentiality.

Read more about Cipher:  Etymology of "Cipher", Ciphers Versus Codes, Types of Cipher, Key Size and Vulnerability

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... any other information to help break a cipher), three factors above all, count Mathematical advances that allow new attacks or weaknesses to be discovered and ... found at Key Length which uses multiple reports to suggest that a symmetric cipher with 128 bits, an asymmetric cipher with 3072 bit keys, and an elliptic curve cipher with 512 bits, all have similar ... considerations, that any theoretically unbreakable cipher must have keys which are at least as long as the plaintext, and used only once one-time pad ...
Cipher (comics) - Fictional Character Biography
... Tager, reveals herself at the end of Young X-Men #8, however her codename is spelled "Cipher" rather than "Cypher" (as it is spelled in earlier mentions) ... Cyclops reveals that Cipher was first discovered during events depicted in New X-Men vol ... a secret per her request, giving her the codename "Cipher," an act made easier by Alisa's mutant ability to become completely undetectable either psychically or physically ...
Cipher (newuniversal) - Fictional Character Biography - Project Spitfire
... The original suit was created by Anthony Stark in 1959 who became Cipher in the "The Fireworks" event in 1955, and is an alternate version of Tony Stark (Iron Man) from the mainstream ... Swann herself was transformed by the White Event when the Cipher glyph bonded with her, acquiring similar superhuman abilities as Anthony Stark (the ... The superhuman abilities granted by the Cipher glyph allowed her to swiftly complete the H.E.X ...

Famous quotes containing the word cipher:

    It is not an arbitrary “decree of God,” but in the nature of man, that a veil shuts down on the facts of to-morrow; for the soul will not have us read any other cipher than that of cause and effect. By this veil, which curtains events, it instructs the children of men to live in to-day.
    Ralph Waldo Emerson (1803–1882)

    The eye is the first circle; the horizon which it forms is the second; and throughout nature this primary figure is repeated without end. It is the highest emblem in the cipher of the world.
    Ralph Waldo Emerson (1803–1882)