  Mobile computing devices have been used broadly to store, manage and process
sensitive or even mission critical data. To protect confidentiality of data
stored in mobile devices, major mobile operating systems use full disk
encryption, which relies on traditional encryption mechanisms and requires that
decryption keys will not be disclosed. This however, is not necessarily true,
since an active attacker may coerce victims for decryption keys. Plausibly
deniable encryption (PDE) can defend against such a coercive attacker by
disguising the true secret key with a decoy key. Leveraging concept of PDE,
various deniable storage systems have been built for both PC and mobile
platforms. However, a secure PDE system for mobile devices is still missing
which can be compatible with mainstream mobile devices and, meanwhile, remains
secure when facing a strong multi-snapshot adversary. In this work, we propose
a preliminary PDE system design for mobile computing devices using flash memory
as underlying storage medium. Ours is the first secure PDE system for mobile
devices which has the following new design features: 1) it is compatible with
mainstream mobile devices due to its integration of PDE into flash translation
layer (FTL), the most popular form of flash memory being used by modern mobile
devices; and 2) it can defend against the multi-snapshot adversary by denying
hidden writes (over the flash memory) caused by hidden sensitive data using
random dummy writes.
