,
Daniel Noble
,
Rafail Ostrovsky
Creative Commons Attribution 4.0 International license
A Distributed Oblivious RAM is a multi-party protocol that securely implements a RAM functionality on secret-shared inputs and outputs. This paper presents two information-theoretically secure DORAMs whose communication costs are asymptotic improvements over the state of the art. Let n be the number of memory locations and let d be the bit-length of each location.
The first, MetaDORAM1, is statistically secure, with n^{-ω(1)} leakage. It has amortized O(log_b(n) d + b ω(1) log(n) + log³(n)/log(log(n))) bits of communication per memory access. Here, b ≥ 2 is a free parameter and ω(1) is any super-constant function (in n). The most communication-efficient prior statistically secure DORAM was that of Abraham et al (PKC 2017), which has cost O(log_b(n) d + b ω(1) log_b(n) log²(n)). MetaDORAM1 is a Θ(ω(1) log(log(n)))-factor improvement over the work of Abraham et al whenever d = O(log²(n)).
The second protocol, MetaDORAM2, achieves perfect security. It has amortized communication cost O(log_b(n)d + b log(n) + log³(n)/log(log(n))) where, again, b ≥ 2 is a free parameter. The best prior perfectly secure DORAM is that of Chan et al (ASIACRYPT 2018) which has communication cost O(log(n) d + log³(n)). MetaDORAM2 is therefore a Ω(log(log(n)))-factor improvement over the DORAM of Chan et al under any parameter range (by setting b = log(n)) and is a Θ(log(n))-factor improvement for d = Ω(n^ε) for any constant ε > 0 (by setting b = d/log(n)). Our work is the first perfectly secure DORAM with sub-logarithmic communication overhead. MetaDORAM2 comes at the cost of a once-off (for any given n) setup phase which requires exponential (in n) computation.
Both DORAMs are in the 3-party setting with security against 1 semi-honest, static corruption. By a trivial transformation, these can be transformed, respectively, into statistically and perfectly secure active 3-server ORAM protocols secure against 1 corrupt server, with the same communication costs. These multi-server ORAM protocols are likewise asymptotic improvements over the state of the art.
@InProceedings{falk_et_al:LIPIcs.ITC.2025.6,
author = {Falk, Brett Hemenway and Noble, Daniel and Ostrovsky, Rafail},
title = {{MetaDORAM: Info-Theoretic Distributed ORAM with Less Communication}},
booktitle = {6th Conference on Information-Theoretic Cryptography (ITC 2025)},
pages = {6:1--6:23},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-385-0},
ISSN = {1868-8969},
year = {2025},
volume = {343},
editor = {Gilboa, Niv},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ITC.2025.6},
URN = {urn:nbn:de:0030-drops-243560},
doi = {10.4230/LIPIcs.ITC.2025.6},
annote = {Keywords: ORAM, MPC, DORAM, multi-server ORAM, active ORAM}
}