From CryptoDox, The Online Encyclopedia on Cryptography and
Information Security In cryptography, the key size
(alternatively key length) is the size of the digits used to
create an encrypted text; it is therefore also a measure of the
number of possible keys which can be used in a cipher, and the
number of keys which must be tested to 'break' the encryption if
no faster means is available. In an ideal encryption system, the
key length is therefore a measure of how secure the data is, and
the effort and time needed to decrypt it by force. The length of
a key is therefore critical in determining the susceptibility of
a cipher to exhaustive search attacks. Because modern
cryptography uses binary keys, the length is usually specified
in bits. The time and effort needed to break a cipher of a given
key size varies according to the cipher; therefore a 128 bit key
size in one system may be deemed equivalent in security to a
1024 bit key size in another. Keys are used to control the
operation of a cipher so that onl