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:
“With one day’s reading a man may have the key in his hands.”
—Ezra Pound (1885–1972)
“...there are important considerations in the world beyond plain sewing and teaching dull little boys the alphabet. Any woman who has brains and willing hands finds twenty remunerative occupations open to her where formerly she would have found merely the inevitable two—plain sewing, or the dull little boys. All she had to do is to make her choice and then buckle on her armor of perseverance, while the world applauds.”
—Clara (Marquise)