Two Sequential Squaring Verifiable Delay Function

Abstract: A Verifiable Delay Function (VDF) is a function that takes a specified sequential time to be evaluated, but can be efficiently verified. VDFs are useful in several applications ranging from randomness beacons to sustainable blockchains but are really rare in practice. Most of the VDFs are based on algebraic assumptions like time-lock puzzle in unknown group orders [6, 8] and isogenies over pairing groups [4]. The number of modulo squaring required for verification in the time-lock puzzle based VDFs are proportional to their security parameter. This paper proposes a verifiable delay function that requires only 2- modulo squaring for verification. So the sequential effort required for verification is independent of the security parameter.