Paper 2024/1468

Dense and smooth lattices in any genus

Abstract

The Lattice Isomorphism Problem (LIP) was recently introduced as a new hardness assumption for post-quantum cryptography. The strongest known efficiently computable invariant for LIP is the genus of a lattice. To instantiate LIP-based schemes one often requires the existence of a lattice that (1) lies in some fixed genus, and (2) has some good geometric properties such as a high packing density or small smoothness parameter. In this work we show that such lattices exist. In particular, building upon classical results by Siegel (1935), we show that essentially any genus contains a lattice with a close to optimal packing density, smoothing parameter and covering radius. We present both how to efficiently compute concrete existence bounds for any genus, and asymptotically tight bounds under weak conditions on the genus.