Covert Channels through Random Number Generator: Mechanisms, Capacity Estimation and Mitigations

Abstract

Covert channels present serious security threat because they allow secret communication between two malicious processes even if the system inhibits direct communication. We describe, implement and quantify a new covert channel through shared hardware random number generation (RNG) module that is available on modern processors. We demonstrate that a reliable, high-capacity and low-error covert channel can be created through the RNG module that works across CPU cores and across virtual machines. We quantify the capacity of the RNG channel under different settings and show that transmission rates in the range of 7-200 kbit/s can be achieved depending on a particular system used for transmission, assumptions, and the load level. Finally, we describe challenges in mitigating the RNG channel, and propose several mitigation approaches both in software and hardware.