A cryptographic hash function is a hash function which is considered practically impossible to invert, that is, to recreate the input data from its hash value alone.These one-way hash functions have been called the workhorses of modern cryptography.The input data is often called the message, and the hash value is often called the message digest or simply the digest. The ideal cryptographic hash function has four main properties:1  it is easy to compute the hash value for any given message. 2  it is infeasible to generate a message from its hash.hese one-way hash functions have been called the workhorses of modern cryptography. The input data is often called the message, and the hash value is often called the message digest or simply the digest.