A New Approach to Post-Quantum Non-Malleability

We provide the first constant-round construction of post-quantum non-malleable commitments under the minimal assumption that post-quantum one-way functions exist. We achieve the standard notion of non-malleability with respect to commitments. Prior constructions required $\Omega\left(\log ^{*} \lambda\right)$ rounds under the same assumption. We achieve our results through a new technique for constant-round non-malleable commitments which is easier to use in the post-quantum setting. The technique also yields an almost elementary proof of security for constant-round non-malleable commitments in the classical setting, which may be of independent interest. When combined with existing work, our results yield the first constant-round quantum-secure multiparty computation for both classical and quantum functionalities in the plain model, under the polynomial hardness of quantum fully-homomorphic encryption and quantum learning with errors.