Modern computer architectures share physical resources between different programs in order to increase area-, energy-, and cost-efficiency. Unfortunately, sharing often gives rise to side channels that can be exploited for extracting or transmitting sensitive information. We currently lack techniques for systematic reasoning about this interplay between efficiency and performance. In particular, there is no established way for quantifying security properties of shared caches.

In this talk, we present a model that enables us to characterise important security properties of caches. Our model encompasses two aspects: (1) The amount of information that is absorbed by a cache, and (2) the amount of information that can effectively be extracted from the cache by an adversary. We use our model to compute both quantities for common cache replacement policies (FIFO, LRU, and PLRU) and to compare their isolation properties. We further show how our model for information extraction leads to an algorithm which we used to improve the bounds delivered by the CacheAudit static analyser.