cryptography salt & nonce
2013-03-19some OS's use Seed SALT or NONCE random values added to the encryption process to add more complexity Something a user has Key swipe card access card badge PASSWORDS.
Salt (cryptography)
In cryptography, a salt is random data that is used as an additional input to a one-way function that hashes a password or passphrase.Cryptographic salts are broadly used in many modern computer systems, from Unix system credentials to Internet security.Salts are closely related to the concept of nonce.
Cryptographic nonce
In security engineering, nonce (Number Once) is an arbitrary number used only once in a cryptographic communication. It is similar in spirit to a nonce word, hence the name. It is often a random or pseudo-random number issued in an authentication protocol to ensure that old communications cannot be reused in replay attacks.
参考：
http://en.wikipedia.org/wiki/Salt_(cryptography)
http://en.wikipedia.org/wiki/Cryptographic_nonce