Bo Chen

Bo Chen

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.

Li Lei, Kai Cong, Zhenkun Yang et al.

Hardware/Software (HW/SW) interfaces, mostly implemented as devices and device drivers, are pervasive in various computer systems. Nowadays HW/SW interfaces typically undergo intensive testing and validation before release, but they are still unreliable and insecure when deployed together with computer systems to end users. Escaped logic bugs, hardware transient failures, and malicious exploits are prevalent in HW/SW interactions, making the entire system vulnerable and unstable. We present HW/SW co-monitoring, a runtime co-verification approach to detecting failures and malicious exploits in device/driver interactions. Our approach utilizes a formal device model (FDM), a transaction-level model derived from the device specification, to shadow the real device execution. Based on the co-execution of the device and FDM, HW/SW co-monitoring carries out two-tier runtime checking: (1) device checking checks if the device behaviors conform to the FDM behaviors; (2) property checking detects invalid driver commands issued to the device by verifying system properties against driver/device interactions. We have applied HW/SW co-monitoring to five widely-used devices and their Linux drivers, discovering 9 real bugs and vulnerabilities while introducing modest runtime overhead. The results demonstrate the major potential of HW/SW co-monitoring in improving system reliability and security.