A “Key Derivation Function” (KDF) derives one or more secret keys from a secret value such as a master key or other known information such as a password using a pseudo-random function.

The most common use of KDFs is the password hashing approach to password verification, as used by the password file or shadow password file. KDFs happen to have the characteristics desired for a “password hash function”, even though they weren’t originally designed for this purpose.

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