Improved hardness results for unique shortest vector problem

We give several improvements on the known hardness of the unique shortest vector problem. - We give a deterministic reduction from the shortest vector problem to the unique shortest vector problem. As a byproduct, we get deterministic NP-hardness for unique shortest vector problem in the ${\mathrm{\ell }}_{\mathrm{\infty }}$ norm. - We give a randomized reduction from SAT to uSVP_{1+1/poly(n)}. This shows that uSVP_{1+1/poly(n)} is NP-hard under randomized reductions. - We show that if GapSVP_\gamma \in coNP (or coAM) then uSVP_{\sqrt{\gamma}} \in coNP (coAM respectively). This simplifies previously known uSVP_{n^{1/4}} \in coAM proof by Cai \cite{Cai98} to uSVP_{(n/\log n)^{1/4}} \in coAM, and additionally generalizes it to uSVP_{n^{1/4}} \in coNP.

• We give a deterministic reduction from search-uSVP_\gamma to the decision-uSVP_{\gamma/2}. We also show that the decision-uSVP is {\bf NP}-hard for randomized reductions, which does not follow from Kumar-Sivakumar \cite{KS01}.