Can the Government Compel Decryption? Don't Trust -- Verify

TL;DR

This paper introduces a formal framework to analyze when courts can compel individuals to perform actions like decryption, emphasizing the burden of proof on the government and applying it to cryptographic primitives including deniable encryption.

Contribution

It proposes a new formal concept of demonstrability and a language to assess whether compelled actions implicitly reveal testimony, advancing legal and cryptographic analysis.

Findings

Framework determines when actions are a foregone conclusion.

Analysis shows government cannot compel decryption of deniable encryption.

Introduces a formal language for assessing compelled acts.

Abstract

If a court knows that a respondent knows the password to a device, can the court compel the respondent to enter that password into the device? In this work, we propose a new approach to the foregone conclusion doctrine from Fisher v US that governs the answer to this question. The Holy Grail of this line of work would be a framework for reasoning about whether the testimony implicit in any action is already known to the government. In this paper we attempt something narrower. We introduce a framework for specifying actions for which all implicit testimony is, constructively, a foregone conclusion. Our approach is centered around placing the burden of proof on the government to demonstrate that it is not "rely[ing] on the truthtelling" of the respondent. Building on original legal analysis and using precise computer science formalisms, we propose demonstrability as a new central concept for describing compelled acts. We additionally provide a language for whether a compelled action meaningfully entails the respondent to perform in a manner that is 'as good as' the government's desired goal. Then, we apply our definitions to analyze the compellability of several cryptographic primitives including decryption, multifactor authentication, commitment schemes, and hash functions. In particular, our framework reaches a novel conclusion about compelled decryption in the setting that the encryption scheme is deniable: the government can compel but the respondent is free to use any password of her choice.