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A Proposal for Assisted Private Information Retrieval

Private Information Retrieval (PIR) addresses the cryptographic problem of hiding sensitive database queries form database operators. In practice, PIR schemes suﬀer from either high computational costs or from restrictive requirements diﬃcult to justify in practical settings. In this work, we introduce Assisted Private Information Retrieval (APIR), a new PIR problem for keyword-value databases which generalizes and relaxes the database consistency assumption in multi-server PIR. Leveraging the decentralized nature of Domain Name Service (DNS), APIR is able to address a privacy issue inherent to encrypted DNS proposals such as DNS-over-HTTPS (DoH) by preventing DNS operators from collecting sensitive data. We propose a construction of Synchronized APIR , an eﬃcient hybrid APIR scheme between black-box single-server PIR and non-black-box multi-server PIR. We apply Synchronized APIR to a proof-of-concept protocol for private DNS query, and demonstrate that APIR is able to outperform the baseline single-server PIR protocol after the initial one-time cost.