Conference Paper

# An Efficient and Parallel Gaussian Sampler for Lattices.

DOI: 10.1007/978-3-642-14623-7_5 Conference: Advances in Cryptology - CRYPTO 2010, 30th Annual Cryptology Conference, Santa Barbara, CA, USA, August 15-19, 2010. Proceedings

Source: DBLP

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**ABSTRACT:**The smoothing parameter $\eta_{\epsilon}(\mathcal{L})$ of a Euclidean lattice $\mathcal{L}$, introduced by Micciancio and Regev (FOCS'04; SICOMP'07), is (informally) the smallest amount of Gaussian noise that "smooths out" the discrete structure of $\mathcal{L}$ (up to error $\epsilon$). It plays a central role in the best known worst-case/average-case reductions for lattice problems, a wealth of lattice-based cryptographic constructions, and (implicitly) the tightest known transference theorems for fundamental lattice quantities. In this work we initiate a study of the complexity of approximating the smoothing parameter to within a factor $\gamma$, denoted $\gamma$-${\rm GapSPP}$. We show that (for $\epsilon = 1/{\rm poly}(n)$): $(2+o(1))$-${\rm GapSPP} \in {\rm AM}$, via a Gaussian analogue of the classic Goldreich-Goldwasser protocol (STOC'98); $(1+o(1))$-${\rm GapSPP} \in {\rm coAM}$, via a careful application of the Goldwasser-Sipser (STOC'86) set size lower bound protocol to thin spherical shells; $(2+o(1))$-${\rm GapSPP} \in {\rm SZK} \subseteq {\rm AM} \cap {\rm coAM}$ (where ${\rm SZK}$ is the class of problems having statistical zero-knowledge proofs), by constructing a suitable instance-dependent commitment scheme (for a slightly worse $o(1)$-term); $(1+o(1))$-${\rm GapSPP}$ can be solved in deterministic $2^{O(n)} {\rm polylog}(1/\epsilon)$ time and $2^{O(n)}$ space. As an application, we demonstrate a tighter worst-case to average-case reduction for basing cryptography on the worst-case hardness of the ${\rm GapSPP}$ problem, with $\tilde{O}(\sqrt{n})$ smaller approximation factor than the ${\rm GapSVP}$ problem. Central to our results are two novel, and nearly tight, characterizations of the magnitude of discrete Gaussian sums.12/2014; - [Show abstract] [Hide abstract]

**ABSTRACT:**Most lattice-based cryptographic schemes are built upon the assumed hardness of the Short Integer Solution (SIS) and Learning With Errors (LWE) problems. Their efficiencies can be drastically improved by switching the hardness assumptions to the more compact Ring-SIS and Ring-LWE problems. However, this change of hardness assumptions comes along with a possible security weakening: SIS and LWE are known to be at least as hard as standard (worst-case) problems on euclidean lattices, whereas Ring-SIS and Ring-LWE are only known to be as hard as their restrictions to special classes of ideal lattices, corresponding to ideals of some polynomial rings. In this work, we define the Module-SIS and Module-LWE problems, which bridge SIS with Ring-SIS, and LWE with Ring-LWE, respectively. We prove that these average-case problems are at least as hard as standard lattice problems restricted to module lattices (which themselves generalize arbitrary and ideal lattices). As these new problems enlarge the toolbox of the lattice-based cryptographer, they could prove useful for designing new schemes. Importantly, the worst-case to average-case reductions for the module problems are (qualitatively) sharp, in the sense that there exist converse reductions. This property is not known to hold in the context of Ring-SIS/Ring-LWE: Ideal lattice problems could reveal easy without impacting the hardness of Ring-SIS/Ring-LWE.Designs Codes and Cryptography 01/2014; · 0.73 Impact Factor - [Show abstract] [Hide abstract]

**ABSTRACT:**Modern lattice-based public-key cryptosystems require sampling from discrete Gaussian (normal) distributions. The paper surveys algorithms to implement such sampling efficiently, with particular focus on the case of constrained devices with small on-board storage and without access to large numbers of external random bits. We review lattice encryption schemes and signature schemes and their requirements for sampling from discrete Gaussians. Finally, we make some remarks on challenges and potential solutions for practical lattice-based cryptography.Applicable Algebra in Engineering Communication and Computing 01/2014; 25(3). · 0.56 Impact Factor

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