Unkeyed DEPIR ⇒ cPIR

Fully-black-box reduction · standard model · folklore

Statement

Every unkeyed DEPIR scheme is a single-server PIR whose database is preprocessed by the server itself: $\mathsf{Setup}(1^{\lambda },DB)$ is deterministic, so the server runs it and knows everything the unkeyed privacy adversary is given, and the query phase is a two-message PIR with query-time communication and computation at most $p(\lambda )+s(n)$ for a polynomial $p$ and a function $s(n)=o(n)$; correctness and query privacy carry over unchanged — folklore.

Notes

• Keyed DEPIR does not give a two-party PIR this way: public-key DEPIR needs a trusted party to preprocess the database — LMW23 — and in secret-key DEPIR the client runs $\mathsf{Setup}$ on the database — BIPW17.