The University of SydneyPage 29Public Key Cryptographysymmetric key crypto–requires sender, receiver know shared secret key–Q: how to agree on key in first place (particularly if never “met”)?public key crypto§radically different approach [Diffie-Hellman76, RSA78]§sender, receiver do notshare secret key§publicencryption key known toall§privatedecryption key known only to receiver