A censoring server cannot selectively withhold PIR responses for a targeted file while honestly answering others: if a PPT algorithm A could distinguish targeted-file queries from all other queries, it would directly violate the query privacy of the underlying PIR scheme. The server's only compliant evasion strategy is an indiscriminate shutdown — refusing all queries or all signatures — which is behaviorally distinguishable and does not produce a plausible-deniability defense.
From 2018-martiny-proof-of-censorship — Proof-of-Censorship: Enabling centralized censorship-resistant content providers
· §4.3
· 2018
· Financial Cryptography and Data Security
Implications
PIR-based accountability schemes force content providers into an all-or-nothing choice: either serve all files honestly or provably censor at least one, eliminating the selective-suppression attack that undermines naive periodic-audit approaches.
Any accountability system relying on challenge-response audits without query-privacy guarantees remains vulnerable to selective non-response; PIR is the load-bearing primitive that closes this gap.