Cache SideChannel Attacks: FlushFlush and the Countermeasures Time Gap In cloud computing, profitability among others, is the driving force that encourages full utilization of computing resources. Hence, scenarios where one or more users are colocated on the same CPU but on different virtual machines are normal. Even though this setting brings profitability, unfortunately it also brings security and privacy issues. Softwarebased sandboxing techniques are not perfect, as a result, users through the shared memory of an application, can leak secret information. To tackle this problem, some work has been published proving how it is possible to detect cache sidechannel attacks using HPCs (Hardware Performance Counters). However, this particular method of detection may only be effective for cache sidechannel attacks that cause a lot of cache activity, especially in the form of cache misses, among others. Using HPCs, we observe that the Firefox Web Browser (a benign application) causes more pagefaults and cache misses among others, in comparison with the FLUSHFLUSH, FLUSHRELOAD and PRIMEPROBE in our attack. In this paper, we focus on using the FLUSHFLUSH method of cache sidechannel attacks, to distinguish between input against the Links textbased browser in order to gain private information about last visited websites. Because the FLUSHFLUSH attack method causes little or no cache misses, as a result, the attack is more stealthy and in some cases more accurate compared to the state of the art FLUSHRELOAD attack method. We make the assumption that both the victim and the adversary are colocated on the same CPU but on different virtual machines and different cores, and that they have the same application installed, then through the shared memory of the application, the attack is made possible. Our experiment results indicate that the shared memory of computer applications may be vulnerable to cache sidechannel attacks and that more work needs to be done to protect users in the cloud computing system in this aspect.

Multilibrary Coded Caching with Partial Secrecy The paper considers a coded caching setup with two libraries and where only one of them needs to be kept secret from an external eavesdropper. We provide upper and lower bounds on the secrecy ratememory tradeoff for systems with mathsfK  2 or mathsfK  3 receivers. Our bounds are tight in some regimes and show that the standard (nonsecure) coded caching upper bound can be approached for a wide range of parameters. In some cases, the proposed upper bound on the secrecy ratememory tradeoff is even lower than the lower bound for standard coded caching. The reason is that in our setup the ratio of receivers requesting secure files over those requesting nonsecure files is fixed and known to everyone in advance. The transmitter can thus adjust the contents stored in the cache memories to this ratio.