Deniable Encryption in Replacement of Untappable Channel to Prevent Coercion

Abstract

The incoerciblety to prevent rigging in e-voting and e-auction have been studied in different literatures. It is realized that the notion of a virtual booth and untappable channel are required to prevent coerciveness. Virtual booth protects the candidates to cast their private values without being observed by the adversary/coercer. However the adversary can influence the candidates after their casting. Adversary used to acquire the encrypted votes/bids either from the colluded authorities (voting server, auctioneer) or by eavesdropping the communicating channel. The adversary then coerces the candidates to disclose their private values with their private keys and verifies whether the ciphers are the encryption of the private values. In the prior literatures of e-voting and e-auctioning, threshold-encryption and receipt-free mechanism are used to prevent the coercion and collusion respectively. But they assumed untappable channel to restrict eavesdropping. However, untappable channel is difficult to achieve. It should be a dedicated trusted link or continuous fiber link to implement untappable channel. In this paper we present an alternative of untappable channel using deniable encryption. Deniable encryption does not restrict the adversary to eavesdrop, but if the candidates are coerced, they are able to find a different value v f and can convince the adversary that the ciphers are the encryption of v f , without reveling the true private value v r . Therefore, eavesdropping does not help the coercer, as he may be plausible denied by the candidates. Our scheme is based on public key probabilistic encryption mechanism. We assume that the sender side (candidate) coercion is only possible, that is, the coercer can not coerce the receivers (authorities).