Paper 2019/1075

Private Information Retrieval with Sublinear Online Time

Henry Corrigan-Gibbs and Dmitry Kogan


We present the first protocols for private information retrieval that allow fast (sublinear-time) database lookups without increasing the server-side storage requirements. To achieve these efficiency goals, our protocols work in an offline/online model. In an offline phase, which takes place before the client has decided which database bit it wants to read, the client fetches a short string from the servers. In a subsequent online phase, the client can privately retrieve its desired bit of the database by making a second query to the servers. By pushing the bulk of the server-side computation into the offline phase (which is independent of the client's query), our protocols allow the online phase to complete very quickly—in time sublinear in the size of the database. Our protocols can provide statistical security in the two-server setting and computational security in the single-server setting. Finally, we prove that, in this model, our protocols are optimal in terms of the trade-off they achieve between communication and running time.

Note: This version fixes one typographical error.

Available format(s)
Cryptographic protocols
Publication info
A major revision of an IACR publication in EUROCRYPT 2020
Private Information Retrieval
Contact author(s)
henrycg @ cs stanford edu
dkogan @ cs stanford edu
2022-03-28: last of 4 revisions
2019-09-23: received
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Creative Commons Attribution


      author = {Henry Corrigan-Gibbs and Dmitry Kogan},
      title = {Private Information Retrieval with Sublinear Online Time},
      howpublished = {Cryptology ePrint Archive, Paper 2019/1075},
      year = {2019},
      note = {\url{}},
      url = {}
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