Scrypt is a sequential memory-hard key derivation function. This module provides low-level bindings to the scrypt key derivation function as well as a higher-level password-storage API. It is based on a fast C implementation of scrypt, written by Colin Percival. For further information see http://www.tarsnap.com/scrypt.html.

Scrypt takes three tuning parameters: N, r and p. They affect running time and memory usage:

Memory usage is approximately 128*r*N bytes. Note that the scryptParams function takes log_2(N) as a parameter. As an example, the defaultParams

  log_2(N) = 14, r = 8 and p = 1

lead to scrypt using 128 * 8 * 2^14 = 16M bytes of memory.

Running time is proportional to all of N, r and p. Since it's influence on memory usage is small, p can be used to independently tune the running time.

To allow storing encrypted passwords conveniently in a single database column, the password storage API provides the data type EncryptedPass. It combines a Pass as well as the Salt and ScryptParams used to compute it into a single ByteString, separated by pipe ("|") characters. The Salt and PassHash are base64-encoded. Storing the ScryptParams with the password allows to gradually strengthen password encryption in case of changing security requirements.

A usage example is given below, showing encryption, verification and changing ScryptParams:

>>> encrypted <- encryptPassIO defaultParams (Pass "secret")
>>> print encrypted
EncryptedPass {getEncryptedPass = "14|8|1|Wn5x[SNIP]nM=|Zl+p[SNIP]g=="}
>>> print $ verifyPass defaultParams (Pass "secret") encrypted
(True,Nothing)
>>> print $ verifyPass defaultParams (Pass "wrong") encrypted
(False,Nothing)
>>> let newParams = fromJust $ scryptParams 16 8 1
>>> print $ verifyPass newParams (Pass "secret") encrypted
(True,Just (EncryptedPass {getEncryptedPass = "16|8|1|Wn5x[SNIP]nM=|ZmWw[SNIP]Q=="}))

Bindings to a fast C implementation of scrypt. For password storage, consider using the more convenient higher-level API above.