Unbounded Non-Malleable Non-Interactive Zero Knowledge Protocols for NP

In asynchronous network communication, non-malleability is requiredto resist against man-in-the-middle attack. Based on the existenceof one-way permutation, we propose two unbounded non-malleableNon-interactive zero knowledge (NIZK) protocols. Firstly, by usingNIZK argument of knowledge instead of as abuilding block, we transform 5-rounds concurrent non-malleable zeroknowledge argument in the Common reference string (CRS)model[15] to non-malleable NIZK argument. The transformationachieves optimal round efficiency in the same model. Secondly, wesimplify the second scheme in CRYPO'01[8] by using thetechnique hidden unduplicatable set selection. In thesimplified scheme, the CRS is much shorter and statements to beproved in the two NIZK sub-protocols are simplified.