Oblivious RAM with Worst-Case Logarithmic Overhead

Gilad Asharov*, Ilan Komargodski, Wei Kai Lin, Elaine Shi

*Corresponding author for this work

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

4 Scopus citations


We present the first Oblivious RAM (ORAM) construction that for N memory blocks supports accesses with worst-case O(log N) overhead for any block size Ω(log N) while requiring a client memory of only a constant number of memory blocks. We rely on the existence of one-way functions and guarantee computational security. Our result closes a long line of research on fundamental feasibility results for ORAM constructions as logarithmic overhead is necessary. The previous best logarithmic overhead construction only guarantees it in an amortized sense, i.e., logarithmic overhead is achieved only for long enough access sequences, where some of the individual accesses incur Θ(N) overhead. The previously best ORAM in terms of worst-case overhead achieves O(log2N/ log log N) overhead. Technically, we design a novel de-amortization framework for modern ORAM constructions that use the “shuffled inputs” assumption. Our framework significantly departs from all previous de-amortization frameworks, originating from Ostrovsky and Shoup (STOC ’97), that seem to be fundamentally too weak to be applied on modern ORAM constructions.

Original languageAmerican English
Title of host publicationAdvances in Cryptology – CRYPTO 2021 - 41st Annual International Cryptology Conference, CRYPTO 2021, Proceedings
EditorsTal Malkin, Chris Peikert
PublisherSpringer Science and Business Media Deutschland GmbH
Number of pages31
ISBN (Print)9783030842581
StatePublished - 2021
Event41st Annual International Cryptology Conference, CRYPTO 2021 - Virtual, Online
Duration: 16 Aug 202120 Aug 2021

Publication series

NameLecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)
Volume12828 LNCS
ISSN (Print)0302-9743
ISSN (Electronic)1611-3349


Conference41st Annual International Cryptology Conference, CRYPTO 2021
CityVirtual, Online

Bibliographical note

Publisher Copyright:
© 2021, International Association for Cryptologic Research.


  • Deamortization
  • Oblivious RAM
  • Worst-case overhead


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