40-bit encryption refers to a
key size of forty bits, or five
bytes, for
symmetric encryption; this represents a relatively low level of security. A forty bit length corresponds to a total of 2
40 possible keys. Although this is a large number in human terms (about a
trillion, nearly two hundred times the world's human population), it is possible to break this degree of encryption using a moderate amount of computing power in a
brute-force attack,
i.e., trying out each possible key in turn.