Paper 1999/006

Fast Proof of Plaintext-Knowledge and Deniable Authentication Based on Chinese Remainder Theorem

Roger Fischlin

Abstract

We propose a fast and communication-efficient proof of plaintext-knowledge (PPTK) protocol based on the Chinese Remainder theorem. With a PPTK the receiver of a ciphertext verifies that the sender knows the corresponding cleartext in such a way that a dishonest sender or an eavesdropper does not learn anything about the plaintext except with sub-polynomial probability. We turn any semantically secure public key cryptosystem into an efficient (interactive) one which is immune against adaptive chosen ciphertext attacks by adding the PPTK protocol. Using our PPTK protocol we also derive an efficient protocol for deniable authentication.