Private Information Retrieval for Graph-based Replication with Minimal Subpacketization

TL;DR

This paper introduces new private information retrieval schemes with minimal subpacketization for graph-based replicated databases, improving efficiency and privacy for specific graph structures.

Contribution

It presents the first unit-subpacketization PIR schemes for star and general graphs, with improved rates for certain graph classes.

Findings

Star-graph scheme outperforms previous low-subpacketization schemes.

General graph scheme uses graph decomposition to achieve higher rates.

Extension to multigraphs yields better rates for complete multi-graphs.

Abstract

We design new minimal-subpacketization schemes for information-theoretic private information retrieval on graph-based replicated databases. In graph-based replication, the system consists of $K$ files replicated across $N$ servers according to a graph with $N$ vertices and $K$ edges. The client wants to retrieve one desired file, while keeping the index of the desired file private from each server via a query-response protocol. We seek PIR protocols that have (a) high rate, which is the ratio of the file-size to the total download cost, and (b) low subpacketization, which acts as a constraint on the size of the files for executing the protocol. We report two new schemes which have unit-subpacketization (which is minimal): (i) for a special class of graphs known as star graphs, and (ii) for general graphs. Our star-graph scheme has a better rate than previously known schemes with low subpacketization for general star graphs. Our scheme for general graphs uses a decomposition of the graph via independent sets. This scheme achieves a rate lower than prior schemes for the complete graph, however it can achieve higher rates than known for some specific graph classes. An extension of our scheme to the case of multigraphs achieves a higher rate than previous schemes for the complete multi-graph.