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 240
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
, trying out each possible key in turn.