A Predictive Model for Cache-Based Side Channels in Multicore and Multithreaded Microprocessors

A side channel is an information channel that unintentionally communicates information about a program as a side effect of the implementation. Recent studies have illustrated the use of shared caches as side channels to extract private keys from computationally secure cryptographic applications. The cache side channel is imperfect in the sense that the attacker's ability to detect cache leakage of critical data is limited by the timing issues. Moreover, some detected leakages are due to non-critical data. Thus, it is difficult to assess the degree of vulnerability given the imperfect nature of the side-channel. Similarly, when solutions that further degrade the quality of the channel, but do not necessarily close it completely, are employed, it is difficult to evaluate their effectiveness. To address this need, this paper proposes a mathematical model to evaluate the expected leakage in a cache as a function of the cache parameters and the victim application behavior. We use simulation to quantify these parameters for typical attack scenarios to validate the model. We demonstrate that the proposed model accurately estimates side channel leakage for for AES and Blowfish encryption and decryption on a variety of cache configurations.