bcrypt password-based key derivation
char *pass, size_t
pass_len, const uint8_t
key_len, unsigned int
bcrypt_pbkdf function converts a
password into a byte array suitable for use as an encryption key. The
password and salt values are combined and repeatedly hashed
rounds times. The salt value should be randomly
generated beforehand. The repeated hashing is designed to thwart discovery
of the key via password guessing attacks. The higher the number of rounds,
the slower each attempt will be.
bcrypt_pbkdf() function returns 0 to
indicate success and -1 for failure.
Niels Provos and David Mazieres, A Future-Adaptable Password Scheme, June 1999.
B. Kaliski, PKCS #5: Password-Based Cryptography Specification Version 2.0, RFC 2898, September 2000.
This implementation deviates slightly from the PBKDF2 standard by mixing output key bits nonlinearly. By mixing the output bytes together, an attacker is required to perform all of the work without taking any shortcuts.