A set of rules and procedures for resolving a mathematical and/or logical problem, much as a recipe in a cookbook helps baffled cooks in the kitchen resolve meal problems. A computer program can be viewed as an elaborate algorithm, and in computer science, an algorithm usually indicates a mathematical procedure for solving a recurrent problem. The word algorithm is believed to stem from the name of a mathematician at the Royal Court in Baghdad, Mohammed ibn-Musa al-Khwarizmi (780–850 a.c.).

Today, information security professionals in particular are concerned with cryptographic ­algorithms—those used to encrypt, or encode, messages. Different algorithms have different levels of complexity, which is related to key size. For example, a 41-bit key is twice as hard to crack, or decode, as a 40-bit key. A 128-bit key is a trillion times harder to crack than a 40-bit key.

See Also: Computer; Cryptography or “Crypto”; Encryption or Encipher.