Express: Lowering the Cost of Metadata-hiding Communication with Cryptographic Privacy

Existing systems for metadata-hiding messaging that provide cryptographic privacy properties have either high communication costs, high computation costs, or both. In this paper, we introduce Express, a metadata-hiding communication system that significantly reduces both communication and computatio...

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Bibliographic Details
Published in:arXiv.org 2020-09
Main Authors: Eskandarian, Saba, Corrigan-Gibbs, Henry, Zaharia, Matei, Boneh, Dan
Format: Article
Language:English
Subjects:
Communication
Communications systems
Computation
Costs
Cryptography
Metadata
Privacy
Whistleblowing
Online Access:Get full text
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Summary:Existing systems for metadata-hiding messaging that provide cryptographic privacy properties have either high communication costs, high computation costs, or both. In this paper, we introduce Express, a metadata-hiding communication system that significantly reduces both communication and computation costs. Express is a two-server system that provides cryptographic security against an arbitrary number of malicious clients and one malicious server. In terms of communication, Express only incurs a constant-factor overhead per message sent regardless of the number of users, whereas previous cryptographically-secure systems Pung and Riposte had communication costs proportional to roughly the square root of the number of users. In terms of computation, Express only uses symmetric key cryptographic primitives and makes both practical and asymptotic improvements on protocols employed by prior work. These improvements enable Express to increase message throughput, reduce latency, and consume over 100x less bandwidth than Pung and Riposte, dropping the end to end cost of running a realistic whistleblowing application by 6x.
ISSN:2331-8422