Differential Cache-Collision Timing Attacks on AES with Applications to Embedded CPUs

This paper proposes a new type of cache-collision timing attacks on software implementations of AES. Our major technique is of differential nature and is based on the internal cryptographic properties of AES, namely, on the MDS property of the linear code providing the diffusion matrix used in the MixColumns transform. It is a chosen-plaintext attack where pairs of AES executions are treated differentially. The method can be easily converted into a chosen-ciphertext attack. We also thoroughly study the physical behavior of cache memory enabling this attack. On the practical side, we demonstrate that our theoretical findings lead to efficient realworld attacks on embedded systems implementing AES at the example of ARM9. As this is one of the most wide-spread embedded platforms today [7], our experimental results might make a revision of the practical security of many embedded applications with security functionality necessary. To our best knowledge, this is the first paper to study cache timing attacks on embedded systems.