Miklos Ajtai

We give a random class of n dimensional lattices so that, if

there is a probabilistic polynomial time algorithm which finds a short

vector in a random lattice with a probability of at least 1/2

then there is also a probabilistic polynomial time algorithm which

solves the following three ...
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Miklos Ajtai

We show that the shortest vector problem in lattices

with L_2 norm is NP-hard for randomized reductions. Moreover we

also show that there is a positive absolute constant c, so that to

find a vector which is longer than the shortest non-zero vector by no

more than a factor of ...
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Jin-Yi Cai, Ajay Nerurkar

Recently Ajtai showed that

to approximate the shortest lattice vector in the $l_2$-norm within a

factor $(1+2^{-\mbox{\tiny dim}^k})$, for a sufficiently large

constant $k$, is NP-hard under randomized reductions.

We improve this result to show that

to approximate a shortest lattice vector within a

factor $(1+ \mbox{dim}^{-\epsilon})$, for any

$\epsilon>0$, ...
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Phong Nguyen, Jacques Stern

Recently, Ajtai discovered a fascinating connection

between the worst-case complexity and the average-case

complexity of some well-known lattice problems.

Later, Ajtai and Dwork proposed a cryptosystem inspired

by Ajtai's work, provably secure if a particular lattice

problem is difficult. We show that there is a converse

to the ...
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Boris Hemkemeier, Frank Vallentin

A lattice in euclidean space which is an orthogonal sum of

nontrivial sublattices is called decomposable. We present an algorithm

to construct a lattice's decomposition into indecomposable sublattices.

Similar methods are used to prove a covering theorem for generating

systems of lattices and to speed up variations of the LLL ...
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Daniele Micciancio

Lattices have received considerable attention as a potential source of computational hardness to be used in cryptography, after a breakthrough result of Ajtai (STOC 1996) connecting the average-case and worst-case complexity of various lattice problems. The purpose of this paper is twofold. On the expository side, we present a rigorous ... more >>>

Mårten Trolin

We give a method for approximating any $n$-dimensional

lattice with a lattice $\Lambda$ whose factor group

$\mathbb{Z}^n / \Lambda$ has $n-1$ cycles of equal length

with arbitrary precision. We also show that a direct

consequence of this is that the Shortest Vector Problem and the Closest

Vector Problem cannot ...
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Elmar Böhler

A clone is a set of functions that is closed under generalized substitution.

The set FP of functions being computable deterministically in polynomial

time is such a clone. It is well-known that the set of subclones of every

clone forms a lattice. We study the lattice below FP, which ...
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Vadim Lyubashevsky, Daniele Micciancio

The generalized knapsack problem is the following: given $m$ random

elements $a_1,\ldots,a_m\in R$ for some ring $R$, and a target $t\in

R$, find elements $z_1,\ldots,z_m\in D$ such that $\sum{a_iz_i}=t$

where $D$ is some given subset of $R$. In (Micciancio, FOCS 2002),

it was proved that for appropriate choices of $R$ ...
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Adam Klivans, Alexander A. Sherstov

We give the first representation-independent hardness results for

PAC learning intersections of halfspaces, a central concept class

in computational learning theory. Our hardness results are derived

from two public-key cryptosystems due to Regev, which are based on the

worst-case hardness of well-studied lattice problems. Specifically, we

prove that a polynomial-time ...
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Chris Peikert, Alon Rosen

We demonstrate an \emph{average-case} problem which is as hard as

finding $\gamma(n)$-approximate shortest vectors in certain

$n$-dimensional lattices in the \emph{worst case}, where $\gamma(n)

= O(\sqrt{\log n})$. The previously best known factor for any class

of lattices was $\gamma(n) = \tilde{O}(n)$.

To obtain our ... more >>>

Chris Peikert

We show that for any $p \geq 2$, lattice problems in the $\ell_p$

norm are subject to all the same limits on hardness as are known

for the $\ell_2$ norm. In particular, for lattices of dimension

$n$:

* Approximating the shortest and closest vector in ... more >>>

Zvika Brakerski, Craig Gentry, Vinod Vaikuntanathan

We present a radically new approach to fully homomorphic encryption (FHE) that dramatically improves performance and bases security on weaker assumptions. A central conceptual contribution in our work is a new way of constructing leveled fully homomorphic encryption schemes (capable of evaluating arbitrary polynomial-size circuits), {\em without Gentry's bootstrapping procedure}.

... more >>>Greg Kuperberg, Shachar Lovett, Ron Peled

We show the existence of rigid combinatorial objects which previously were not known to exist. Specifically, for a wide range of the underlying parameters, we show the existence of non-trivial orthogonal arrays, $t$-designs, and $t$-wise permutations. In all cases, the sizes of the objects are optimal up to polynomial overhead. ... more >>>

Elena Grigorescu, Chris Peikert

The question of list decoding error-correcting codes over finite fields (under the Hamming metric) has been widely studied in recent years. Motivated by the similar discrete structure of linear codes and point lattices in $R^{N}$, and their many shared applications across complexity theory, cryptography, and coding theory, we initiate the ... more >>>

Karthekeyan Chandrasekaran, Mahdi Cheraghchi, Venkata Gandikota, Elena Grigorescu

Motivated by the structural analogies between point lattices and linear error-correcting codes, and by the mature theory on locally testable codes, we initiate a systematic study of local testing for membership in lattices. Testing membership in lattices is also motivated in practice, by applications to integer programming, error detection in ... more >>>