Rethinking the adversary and operational characteristics of deniable storage

Aim: With the widespread adoption of disk encryption technologies, it has become common for adversaries to employ coercive tactics to force users to surrender encryption keys. For some users, this creates a need for hidden volumes that provide plausible deniability, the ability to deny the existence of sensitive information. Previous deniable storage solutions only offer pieces of an implementable solution that do not take into account more advanced adversaries, such as intelligence agencies, and operational concerns. Specifically, they do not address an adversary that is familiar with the design characteristics of any deniable system. Methods: We evaluated existing threat models and deniable storage system designs to produce a new, stronger threat model and identified design characteristics necessary in a plausibly deniable storage system. To better explore the implications of this stronger adversary, we developed Artifice, the first tunable, operationally secure, self repairing, and fully deniable storage system. Results: With Artifice, hidden data blocks are split with an information dispersal algorithm such as Shamir Secret Sharing to produce a set of obfuscated carrier blocks that are indistinguishable from other pseudorandom blocks on the disk. The blocks are then stored in unallocated space of an existing file system. The erasure correcting capabilities of an information dispersal algorithm allow Artifice to self repair damage caused by writes to the public file system. Unlike preceding systems, Artifice addresses problems regarding flash storage devices and multiple snapshot attacks through simple block allocation schemes and operational security measures. To hide the user’s ability to run a deniable system and prevent information leakage, a user accesses Artifice through a separate OS stored on an external Linux live disk. Conclusion: In this paper, we present a stronger adversary model and show that our proposed design addresses the primary weaknesses of existing approaches to deniable storage under this stronger assumed adversary.