Abstract

Data confidentiality can be effectively preserved through encryption. In certain situations, this is inadequate, as users may be coerced into disclosing their decryption keys. In this case, the data must be hidden so that its very existence can be denied. Steganographic techniques and deniable encryption algorithms have been devised to address this specific problem. Given the recent proliferation of smartphones and tablets, we examine the feasibility and efficacy of deniable storage encryption for mobile devices. We evaluate existing, and discover new, challenges that can compromise plausibly deniable encryption (PDE) in a mobile environment. To address these obstacles, we design a system called Mobiflage that enables PDE on mobile devices by hiding encrypted volumes within random data on a device’s external storage. We leverage lessons learned from known issues in deniable encryption in the desktop environment, and design new countermeasures for threats specific to mobile systems. Key features of Mobiflage include: deniable file systems with limited impact on throughput; efficient storage use with no data expansion; and restriction/prevention of known sources of leakage and disclosure. We provide a proof-of-concept implementation for the Android OS to assess the feasibility and performance of Mobiflage. We also compile a list of best practices users should follow to restrict other known forms of leakage and collusion that may compromise deniability.