Paper 2022/1089

Pirmission: Single-server PIR with Access Control

Abstract

Databases often require the flexibility to control which entities can access specific database records. Such access control is absent in works that provide private access to databases, namely private information retrieval (PIR) systems. In this paper, we show how to address this shortcoming by introducing Pirmission, the first practical single-server PIR system that allows the enforcement of access control policies. Pirmission’s mechanism does not even reveal whether the client passed or failed the access control check—instead the client receives random data if they are not authorized to access a database record. To demonstrate the usefulness and practicality of Pirmission, we use it to build a private contact discovery platform that allows users to only be discoverable by their friends (who have permission). Compared to state-of- the-art single-server PIR protocols that do not provide access control, Pirmission increases the server’s response time by around 2.8X (much less for databases with large records), and requires only one additional ciphertext to be sent by the client.