Hello from the Other Side: SSH over Robust Cache Covert Channels in the Cloud

Covert channels evade isolation mechanisms between multiple parties in the cloud. Especially cache covert channels allow the transmission of several hundred kilobits per second between unprivileged user programs in separate virtual machines. However, caches are small and shared and thus cache-based communication is susceptible to noise from any system activity and interrupts. The feasibility of a reliable cache covert channel under a severe noise scenario has not been demonstrated yet. Instead, previous work relies on either of the two contradicting assumptions: the assumption of direct applicability of error-correcting codes, or the assumption that noise effectively prevents covert channels.