4 move perfect ZKIP of knowledge with no assumption

Abstract

This paper presents a 4-move perfect ZKIP of knowledge with no cryptographic assumption for the random self reducible problems [TW87] whose domain is NP∩BPP. The certified discrete log problem is such an example. (Finding a witness is more difficult than the language membership problem.) A largely simplified 4-move ZKIP for the Hamilton Circuit problem is also shown. In our ZKIP, a trapdoor coin flipping protocol is introduced to generate a challenge bit. P and V cooperatively generate a random bit in a coin flipping protocol. In a trapdoor coin flipping protocol, V who knows the trapdoor can create the view which he can later reveal in two possible ways: both as head and as tail.