Paper 2026/243 Original: eprint.iacr.org/2026/243 ↗

Towards Making Doubly-Efficient PIR Practical

Abstract

Doubly-efficient private information retrieval (DEPIR) enables sublinear per-query work (in the database size $N$) for both client and server, while requiring no client state. Despite its theoretical promise, single-server DEPIR exhibits a prohibitive concrete efficiency gap: for $N=2^{23}$, the state-of-the-art construction (Eurocrypt '25) requires a 733TB server state and over $2^{37}$ online RAM/Disk reads, rending it infeasible to execute. This paper advances single-server DEPIR towards practicality through a series of algorithmic innovations. Compared with the state-of-the-art, we achieve a 4 orders of magnitude reduction in server state and a 6 orders of magnitude reduction in query time. In particular, for the same level database ($N=2^{23}$), querying $5461$ elements in a single batch requires only 171GB of server state and $2^{24}$ online RAM/disk reads, yielding a 112s total query time and a 21ms amortized query time.