International Association for Cryptologic Research

International Association
for Cryptologic Research


On Computational Shortcuts for Information-Theoretic PIR

Matthew M. Hong
Yuval Ishai
Victor I. Kolobov
Russell W. F. Lai
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Presentation: Slides
Abstract: Information-theoretic {\em private information retrieval} (PIR) schemes have attractive concrete efficiency features. However, in the standard PIR model, the computational complexity of the servers must scale linearly with the database size. We study the possibility of bypassing this limitation in the case where the database is a truth table of a ``simple'' function, such as a union of (multi-dimensional) intervals or convex shapes, a decision tree, or a DNF formula. This question is motivated by the goal of obtaining lightweight {\em homomorphic secret sharing} (HSS) schemes and secure multiparty computation (MPC) protocols for the corresponding families. We obtain both positive and negative results. For ``first-generation'' PIR schemes based on Reed-Muller codes, we obtain computational shortcuts for the above function families, with the exception of DNF formulas for which we show a (conditional) hardness results. For ``third-generation'' PIR schemes based on matching vectors, we obtain stronger hardness results that apply to all of the above families. Our positive results yield new information-theoretic HSS schemes and MPC protocols with attractive efficiency features for simple but useful function families. Our negative results establish new connections between information-theoretic cryptography and fine-grained complexity.
Video from TCC 2020
  title={On Computational Shortcuts for Information-Theoretic PIR},
  booktitle={Theory of Cryptography},
  author={Matthew M. Hong and Yuval Ishai and Victor I. Kolobov and Russell W. F. Lai},