10/20/2011. 2. Overview. Some theory and motivationWhat is a proof?What is knowledge?Interactive proofsZero knowledge proofsZKP and NP languagesApplicationsBrainstorming. 10/20/2011. 3. Motivation. Two millionaire problemAlice and Bob are two millionaires who want to find out which is richer without revealing the amount of their wealth (money!!!)Need verifiable communication among mutually distrusting parties.