Towards secure deletion on smartphones

Abstract

Nowadays, smartphones constitute one of the most commonly used electronic devices. Today's smartphones combine a variety of different technologies: they offer in addition to excellent mobile availability and connectivity also high-speed data transfer for the user. Moreover, they are multimedia capable due to their integrated digital camera or music player, and offer a wide variety of communication services like e-mail, SMS or MMS. Consequently, they are used increasingly as a “mobile office”. In this paper, we outline the possibilities and obstacles of secure deletion, namely the problem of deleting sensitive data on a smartphone in such a way that this data cannot be restored during a later forensic investigation. In order to guarantee the complete deletion of data, it would be necessary to access the memory chip directly such that we can overwrite the address space of existing data with arbitrary data. However, this approach is not possible when dealing with smartphones due to several reasons. On the one hand, the user's activities are restricted on the device, which implies that farreaching system interventions cannot be conducted easily. On the other hand, writing on a specific physical address is hindered due to the use of “wear leveling” algorithms on flash chips, which are intended to optimize durability. We discuss these problems in detail and introduce an approach to more securely delete data under certain constraints.