Biscuit: New MPCitH Signature Scheme from Structured Multivariate Polynomials

This paper describes Biscuit, a new multivariate-based signature scheme derived using the MPC-in-the-Head (MPCitH) approach. The security of Biscuit is related to the problem of solving a set of structured quadratic algebraic equations. These equations are highly compact and can be evaluated using very few multiplications (one multiplication per equation). The core of Biscuit is a rather simple MPC protocol for secure multiplications using standard optimized multiplicative triples. This paper also includes several improvements toward the initial version of Biscuit submitted to the NIST PQC standardization process for additional signature schemes. Notably, we introduce a new hypercube variant of Biscuit, refine the security analysis with recent third-party attacks, and present a new AVX2 implementation of Biscuit.