The scrypt key derivation function was originally developed for use in the Tarsnap online backup system and is designed to be far more secure against hardware brute-force attacks than alternative functions such as PBKDF2 or bcrypt.

We estimate that on modern (2009) hardware, if 5 seconds are spent computing a derived key, the cost of a hardware brute-force attack against scrypt is roughly 4000 times greater than the cost of a similar attack against bcrypt (to find the same password), and 20000 times greater than a similar attack against PBKDF2.

Details of the scrypt key derivation function are given in:

Some additional articles may be of interest: