Universal arguments and their applications

We put forward a new type of computationally-sound proof systems, called universal-arguments, which are related but different from both CS-proofs (as defined by Micali, 2000) and arguments (as defined by Brassard et al., 1986). In particular, we adopt the instance-based prover-efficiency paradigm of CS-proofs, but follow the computational-soundness condition of argument systems (i.e., we consider only cheating strategies that are implementable by polynomial-size circuits). We show that universal-arguments can be constructed based on standard intractability assumptions that refer to polynomial-size circuits (rather than assumptions referring to subexponential-size circuits as used in the construction of CS-proofs). As an application of universal-arguments, we weaken the intractability assumptions used in the recent non-black-box zero-knowledge arguments of Barak (2001). Specifically, we only utilize intractability assumptions that refer to polynomial-size circuits (rather than assumptions referring to circuits of some "nice" super-polynomial size).