Analysis of Mitigation Measures for Timing Attacks in Mobile-Cloud Offloading Systems

Abstract

Mobile cloud offloading has been proposed to migrate complex computations from mobile devices to powerful servers. While this may be beneficial from the performance and energy perspective, it certainly exhibits new challenges in terms of security due to increased data transmission over networks with potentially unknown threats. Among possible security issues are timing attacks which are not prevented by traditional cryptographic security. Usually random delays are introduced in such systems as a popular countermeasure. Random delays are easily deployed even if the source code of the application is not at hand. While the benefits are obvious, a random delay introduces a penalty that should be minimized. The challenge is to select the distribution from which to draw the random delays and to set mean and variance in a suitable way such that the system security is maximized and the overhead is minimized. To tackle this problem, we have implemented a prototype that allows us to compare the impact of different random distributions on the expected success of timing attacks. Based on our model, the effect of random delay padding on the performance and security perspective of offloading systems is analyzed in terms of response time and optimal rekeying rate. We found that the variance of random delays is the primary influencing factor to the mitigation effect. Based on our approach, the system performance and security can be improved as follows. Starting from the mission time of a computing job one can select a desired padding policy. From this the optimal rekeying interval can be determined for the offloading system.