# cryptographic hash function

Hello, I'm writing a Sage program to implement a Public Key Cryptographic scheme and I need a cryptographic hash function that takes as input a binary string of a given size d_domain and outputs a binary string of a given size d_range. I read the documentation of the package Crypto.Hash, but I don't understand how to use the hash functions there. Can someone help me? Example parameters are: d_domain = d_range = 256