Key Choice
To prevent a key from being guessed, keys need to be generated truly randomly and contain sufficient entropy. The problem of how to safely generate truly random keys is difficult, and has been addressed in many ways by various cryptographic systems. There is a RFC on generating randomness (RFC 4086, Randomness Requirements for Security). Some operating systems include tools for "collecting" entropy from the timing of unpredictable operations such as disk drive head movements. For the production of small amounts of keying material, ordinary dice provide a good source of high quality randomness.
When a password (or passphrase) is used as an encryption key, well-designed cryptosystems first run it through a key derivation function which adds a salt and compresses or expands it to the key length desired, for example by compressing a long phrase into a 128-bit value suitable for use in a block cipher.
Read more about this topic: Key (cryptography)
Famous quotes containing the words key and/or choice:
“The key word in my plays is “perhaps.””
—Samuel Beckett (1906–1989)
“European society has always been divided into classes in a way that American society never has been. A European writer considers himself to be part of an old and honorable tradition—of intellectual activity, of letters—and his choice of a vocation does not cause him any uneasy wonder as to whether or not it will cost him all his friends. But this tradition does not exist in America.”
—James Baldwin (1924–1987)