We prove new upper bounds on the size of families of vectors in $\Z_m^n$ with restricted modular inner products, when $m$ is a large integer. More formally, if $\vec{u}_1,\ldots,\vec{u}_t \in \Z_m^n$ and $\vec{v}_1,\ldots,\vec{v}_t \in \Z_m^n$ satisfy $\langle\vec{u}_i,\vec{v}_i\rangle\equiv0\pmod m$ and $\langle\vec{u}_i,\vec{v}_j\rangle\not\equiv0\pmod m$ for all $i\neq j\in[t]$, we prove that $t \leq ... more >>>

A Matching Vector ($\mathbf{MV}$) family modulo a positive integer $m \ge 2$ is a pair of ordered lists $\mathcal{U} = (\mathbf{u}_1, \cdots, \mathbf{u}_K)$ and $\mathcal{V} = (\mathbf{v}_1, \cdots, \mathbf{v}_K)$ where $\mathbf{u}_i, \mathbf{v}_j \in \mathbb{Z}_m^n$ with the following property: for any $i \in [K]$, the inner product $\langle \mathbf{u}_i, \mathbf{v}_i \rangle ... more >>>

In this paper, we construct new t-server Private Information Retrieval (PIR) schemes with communication complexity subpolynomial in the previously best known, for all but finitely many t. Our results are
based on combining derivatives (in the spirit of Woodruff-Yekhanin) with the Matching Vector
based PIRs of Yekhanin and Efremenko. Previously ... more >>>

In this paper we study a basic and natural question about Fourier analysis of Boolean functions, which has applications to the study of Matching Vector based Private Information Retrieval (PIR) schemes.

For integers $m,r$, define a {\em delta function} on $\{0,1\}^r \subseteq \mathbb Z_m^r$ to be a function $f: ... more >>>

We show that under a plausible number-theoretic conjecture, for any constant $s$ there exists an $s$-server private information retrieval (PIR) protocol that on an $n$-bit database requires communication $\exp(O((\log n)^{1/s} (\log \log n)^{1-1/s}))$. Previous constructions attaining the same communication required $2^{O(s)}$ servers. Our number-theoretic conjecture is implied by existing conjectures, ... more >>>

A Matching Vector ($\mathbf{MV}$) family modulo a positive integer $m\ge 2$ is a
pair of ordered lists $U=(u_1,\ldots,u_K)$ and $V=(v_1,\ldots,v_K)$ with
$u_i,v_j\in \Z_m^n$ such that $\langle u_i,v_i\rangle=0 \pmod m$ for every
$i\in[K]$, while $\langle u_i,v_j\rangle\ne 0 \pmod m$ for every $i\ne j$. It
is called $r$-restricted if the set of ... more >>>