Hadamard Product Argument from Lagrange-Based Univariate Polynomials

Hadamard product is a point-wise product for two vectors. This paper presents a new scheme to prove Hadamard-product relation as a sub-protocol for SNARKs based on univariate polynomials. Prover uses linear cryptographic operations to generate the proof containing logarithmic field elements. The verification takes logarithmic cryptographic operations with constant numbers of pairings in bilinear group. The construction of the scheme is based on the Lagrange-based KZG commitments (Kate, Zaverucha, and Goldberg at Asiacrypt 2010) and the folding technique. We construct an inner-product protocol from folding technique on univariate polynomials in Lagrange form, and by carefully choosing the random polynomials suitable for folding technique, we construct a Hadamard-product protocol from the inner-product protocol, giving an alternative to prove linear algebra relations in linear time, and the protocol has a better concrete proof size than previous works.