Protecting Portable Data with Host Validation

The use of portable storage devices such as key-chain USB devices is now ubiquitous. Many use these devices with impunity–repeatedly using the same storage device in open computer laboratories, Internet cafes, and on office and home computers. Such devices are now the target of malware that exploit the data present or use them as a means to propagate malicious software, e.g., Conficker and Agent.bz. This paper presents the Kells mobile storage system. Kells limits untrusted or unknown systems from accessing sensitive data by continuously validating the accessing host’s integrity state. We explore the design and operation of Kells, and implement a proof-of-concept USB 2.0 storage device on experimental hardware. Our analysis of Kells is twofold. We first prove the security of device operation (within a freshness security parameter ∆t) using the LS logic of secure systems. Second, we empirically evaluate the performance of the Kells device. These experiments indicate that the overheads associated with host validation are nominal, showing a worst case throughput overhead of 1.22% for read operations and 2.78% for writes.