What is a cipher?
Q: What is a cipher?
A: A cipher (or cypher) is an algorithm for performing encryption (coding) or decryption (decoding). It is a series of well-defined steps that can be followed as a procedure.
Q: How does one encipher information?
A: To encipher or encode is to convert information from plain text into cipher or code.
Q: What is the difference between a cipher and a code?
A: In non-technical usage, a 'cipher' often means the same thing as a 'code'; but in cryptography, ciphers are distinguished from codes. One 20th century source gives this explanation: a cipher is "a method in which the basic unit of concealment is the letter. In comparison, a code is form of concealment in which the basic unit is the word".
Q: How does encryption work?
A: A cipher is used to turn the original information ("plaintext") to the encrypted form "ciphertext". The ciphertext message contains all the information of the plaintext message, but cannot be read by human or computer without the proper mechanism to decrypt it. To encipher or decipher, you need the "key". In encryption, a key specifies the particular transformation of plaintext into ciphertext, or vice versa during decryption.
Q: How are ciphers divided by type of key used?
A: Ciphers are divided into symmetric key algorithms (private-key cryptography): wherethe same key is used for encryption and decryption; and asymmetric key algorithms (public-key cryptography): where two different keys are used for encryption and decryption.
Q: Where does ‘cipher’ come from?
A:The word 'cipher' comes from French cifre and Medieval Latin cifra, from Arabic sifr meaning 'zero'. The first known English use of zero was in 1598.
