Cryptology ePrint Archive: Report 2021/1341

Anonymous Whistleblowing over Authenticated Channels

Thomas Agrikola and Geoffroy Couteau and Sven Maier

Abstract: The goal of anonymous whistleblowing is to publicly disclose a message while at the same time hiding the identity of the sender in a way that even if suspected of being the sender, this cannot be proven. While many solutions to this problem have been proposed over the years, they all require some form of interaction with trusted or non-colluding parties. In this work, we ask whether this is fundamentally inherent. We put forth the notion of anonymous transfer as a primitive allowing to solve this problem without relying on any participating trusted parties.

We initiate the theoretical study of this question, and derive negative and positive results on the existence of such a protocol. We refute the feasibility of asymptotically secure anonymous transfer, where the message will be received with overwhelming probability while at the same time the identity of the sender remains hidden with overwhelming probability. On the other hand, resorting to fine-grained cryptography, we provide a heuristic instantiation (assuming ideal obfuscation) which guarantees that the message will be correctly received with overwhelming probability and the identity of the sender leaks with vanishing probability. Our results provide strong foundations for the study of the possibility of anonymous communications through authenticated channels, an intriguing goal which we believe to be of fundamental interest.

Category / Keywords: foundations / foundations, whistleblowing, fine-grained cryptography, distribution testing, undetectable computation, anonymous transfer, ideal obfuscation

Date: received 5 Oct 2021

Contact author: couteau at irif fr, thomas agrikola at gmail com, svmaier at ira uni-karlsruhe de

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Version: 20211007:015426 (All versions of this report)

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