Paper 2022/009

Algebraic Reductions of Knowledge

Abhiram Kothapalli and Bryan Parno

Abstract

Arguments of knowledge are powerful cryptographic primitives that allow a prover to demonstrate that it knows a satisfying witness to a prescribed statement. Tremendous progress has been made in developing efficient argument systems by leveraging homomorphic structure in an increasingly composable and recursive manner. However, the extent to which homomorphisms can be composed and manipulated in the service of efficient argument systems is still not well understood. To this end, we introduce reductions of knowledge, a generalization of arguments of knowledge, which reduce checking a statement in one relation to checking a derived statement in another, and better capture the composable and recursive nature of arguments over homomorphisms. We construct and study the tensor reduction, which is capable of reducing any homomorphic statement composed via the tensor product, and provides knowledge soundness unconditionally when working over vector spaces. We show that tensor reductions generalize a large class of prior recursive techniques including the ubiquitous sumcheck protocol. We additionally show that tensor reductions can be employed to construct reductions of knowledge with logarithmic communication for familiar linear algebraic statements, and in turn, these can be composed to recover a reduction of knowledge for NP with logarithmic communication.