Generic yet Practical ZK Arguments from any Public-Coin HVZK

In this work, we present a generic yet practical transformation from any public-coin honest-verifier zero-knowledge (HVZK) protocols to normal zero-knowledge (ZK) arguments. By “generic”, we mean that the transformation is applicable to any public-coin HVZK protocol under any one-way function (OWF) admitting Σ-protocols. By “practical ” we mean that the transformation does not go through general N P-reductions and only incurs additionally one round (for public-coin HVZK protocols of odd number of rounds that is the normal case in practice). In particular, if the starting public-coin HVZK protocols and the underlying Σ-protocols are practical, the transformed ZK arguments are also practical. In addition, our transformation also preserves statistical/perfect zero-knowledge. To this end, we develop generic yet practical 3-round perfectly-hiding equivocal (string) commitment scheme under any OWF admitting Σ-protocols, which is possibly of independent value. We also show that three rounds is the lower-bound of round-complexity for equivocal commitment schemes