Public Key cryptography The inventors Whitfield diffie and martin hellman 1976 Ralph merkle 1978 Trap Door Alice Bob C f (P) B P fk(c, TB Encryption with one-way function Computation of inverse function One-way functions extremely expensive are often based on well Joe known hard problems fk(c) 22 Public Key Cryptography • The Inventors – Whitfield Diffie and Martin Hellman 1976 – Ralph Merkle 1978 C = fKB (P) Encryption with one-way function P = f-1 KB (C,TB) Joe P = f-1 KB (C) Alice Bob KB Computation of inverse function extremely expensive Trap Door One-way functions are often based on well￾known hard problems