Reinterpreting and Improving the Cryptanalysis of the Flash Player PRNG

Abstract

Constant blinding is an efficient countermeasure against just-in-time (JIT) spraying attacks. Unfortunately, this mitigation mechanism is not always implemented correctly. One such example is the constant blinding mechanism found in the Adobe Flash Player. Instead of choosing a strong mainstream pseudo-random number generator (PRNG), the Flash Player designers chose to implement a proprietary one. This led to the discovery of a vulnerability that can be exploited to recover the initial seed used by the PRNG and thus, to bypass the constant blinding mechanism. Using this vulnerability as a starting point, we show that no matter the parameters used by the previously mentioned PRNG it still remains a weak construction. A consequence of this study is an improvement of the seed recovering mechanism from previously known complexity of $\mathcal O(2^{21})$ to one of $\mathcal O(2^{11})$