implementation of https://www.tarsnap.com/scrypt/scrypt.pdf
Output buffer for derived key. Buffer length defines the key length. Lenght < 2^32.
password
cryptographic salt
CPU/memory cost parameter
block size parameter
parallelization parameter. p <= (2^32-1)*hashLen/MFLen
See Implementation
implementation of https://www.tarsnap.com/scrypt/scrypt.pdf