Attacking RSA with Simple Branch Prediction Analysis (SBPA)

Abstract Paper - On the Power of Simple Branch Prediction Analysis

Very recently, a new software side-channel attack, called Branch Prediction Analysis (BPA) attack, has been discovered and also demonstrated to be practically feasible on popular commodity PC platforms. While the above recent attack still had the flavor of a classical timing attack against RSA, where one uses many execution-time measurements under the same key in order to statistically amplify some small but key-dependent timing differences, we dramatically improve upon the former result. We prove that a carefully written spy-process running simultaneously with an RSA-process, is able to collect during one \emph{single} RSA signing execution almost all of the secret key bits. We call such an attack, analyzing the CPU's Branch Predictor states through spying on a single quasi-parallel computation process, a {Simple Branch Prediction Analysis (SBPA)} attack --- sharply differentiating it from those one relying on statistical methods and requiring many computation measurements under the same key. The successful extraction of almost all secret key bits by our SBPA attack against an openSSL RSA implementation proves that the often recommended blinding or so called randomization techniques to protect RSA against side-channel attacks are, in the context of SBPA attacks, totally useless.