SoK: Plausibly Deniable Storage

Abstract

Data privacy is critical in instilling trust and empowering the societal pacts of modern technology-driven democracies. Unfortunately it is under continuous attack by overreaching or outright oppressive governments, including some of the world’s oldest democracies. Increasingly-intrusive anti-encryption laws severely limit the ability of standard encryption to protect privacy. New defense mechanisms are needed. Plausible deniability (PD) is a powerful property, enabling users to hide the existence of sensitive information in a system under direct inspection by adversaries. Popular encrypted storage systems such as TrueCrypt and other research efforts have attempted to also provide plausible deniability. Unfortunately, these efforts have often operated under less well-defined assumptions and adversarial models. Careful analyses often uncover not only high overheads but also outright security compromise. Further, our understanding of adversaries, the underlying storage technologies, as well as the available plausible deniable solutions have evolved dramatically in the past two decades. The main goal of this work is to systematize this knowledge. It aims to: (1) identify key PD properties, requirements and approaches; (2) present a direly-needed unified framework for evaluating security and performance; (3) explore the challenges arising from the critical interplay between PD and modern system layered stacks; (4) propose a new “trace-oriented” PD paradigm, able to decouple security guarantees from the underlying systems and thus ensure a higher level of flexibility and security independent of the technology stack. This work is meant also as a trusted guide for system and security practitioners around the major challenges in understanding, designing and implementing plausible deniability into new or existing systems.

False-Bottom Encryption: Deniable Encryption From Secret Sharing

“…Our security definition does not account for adversaries profiling the access patterns of a user, which calls for additional techniques to either randomize or ''equalize'' all access sequences. Future work will thus investigate extensions to our scheme by means of private information retrieval or other techniques (see the related work, in particular [22]), to analyze if information-theoretic security remains accomplishable or deteriorates against attackers that profile the (physical) device usage.…”

“…An interesting additional security consideration is resilience against leakage of information from access patterns. In a series of papers [20], [21], [22], the focus of VOLUME 11, 2023 plausible deniability constructions was shifted to hiding access patterns, as well as leveraging properties of the physical storage devices, using oblivious RAM among other techniques. Our discussion is agnostic of such physical features and does not hide access patterns as such, since the adversary model used here is only concerned with attacks on a static snapshot of the ciphertext, but allows partial side-information to be available to the adversary (similar as what access patterns could leak).…”