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.
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Famous quotes containing the words key and/or choice:
“‘The key is in the window, the key is in the sunlight at the
window—I have the key—Get married Allen don’t take drugs—the key is in the bars, in the sunlight in the window.
Love,
your mother’”
—Allen Ginsberg (b. 1926)
“Blunders are an inescapable feature of war, because choice in military affairs lies generally between the bad and the worse.”
—Allan Massie (b. 1938)