The University of SydneyPage 47Message digestscomputationally expensive to public-key-encrypt long messages goal: fixed-length, easy-to-compute digital “fingerprint”–apply hash function H to m, get fixed size message digest, H(m).Hash function properties:–many-to-1–produces fixed-size msg digest (fingerprint)–given message digest x, computationally infeasible to find m such that x = H(m)large messagemH: HashFunctionH(m)