ACSAC 2016: Amplifying Side Channels Through Performance Degradation

In this work, accepted to ACSAC 2016, we show that an adversary can amplify a side channel leakage from a victim by slowing the victim down. We apply the technique against a victim that uses the Bitcoin elliptic curve and show that we need to observe only 6 signatures to completely break the private key.  The work was done in collaboration with Billy Brumley (Tampere University of Technology) and Joop van de Pol (Bristol University).

T. Allan, B. B. Brumley, K. Falkner, J. van de Pol and Y. Yarom, Amplifying Side Channels Through Performance Degradation, ACSAC 2016, Los Angeles, CA, US, Dec 2016.
Abstract: Interference between processes executing on shared hardware can be used to mount performance-degradation attacks. However, in most cases, such attacks offer little benefit for the adversary. In this paper, we demonstrate that software-based performance-degradation attacks can be used to amplify side-channel leaks, enabling the adversary to increase both the amount and the quality of information captured.
We identify a new information leak in the OpenSSL implementation of the ECDSA digital signature algorithm, albeit seemingly unexploitable due to the limited granularity of previous trace procurement techniques. To overcome this imposing hurdle, we combine the information leak with a microarchitectural performance-degradation attack that can slow victims down by a factor of over 150. We demonstrate how this combination enables the amplification of a side-channel sufficiently to exploit this new information leak. Using the combined attack, an adversary can break a private key of the secp256k1 curve, used in the Bitcoin protocol, after observing only 6 signatures—a four-fold improvement over all previously described attacks.

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