Cryptographic Deniability: A Multi-perspective Study of User Perceptions and Expectations

Cryptographic deniability allows a sender to deny authoring a message. However, it requires social and legal acceptance to be effective. Although popular secure messaging apps support deniability, security experts are divided on whether it should be the default property for these applications. This paper presents a multi-perspective, multi-methods study of user perceptions and expectations of deniability. The methodology includes (1) qualitative analysis of expert opinions obtained from a public forum on deniability, (2) qualitative analysis of semi-structured interviews of US participants, (3) quantitative analysis of a survey (n=664) of US participants, and (4) qualitative and quantitative analysis of US court cases with help from a legal expert to understand the legal standpoint of deniability. The results show that deniability is not socially accepted, and most users prefer non-repudiation. We found no US court cases involving WhatApp that consider deniability. Significant human-centered research is needed before deniability can adequately protect vulnerable users.