CrySL: An Extensible Approach to Validating the Correct Usage of Cryptographic APIs

Various studies have empirically shown that the majority of Java and Android applications misuse cryptographic libraries, causing devastating breaches of data security. It is crucial to detect such misuses early in the development process. To detect cryptography misuses, one must define secure uses first, a process mastered primarily by cryptography experts but not by developers. In this paper, we present CrySL, a specification language for bridging the cognitive gap between cryptography experts and developers. CrySL enables cryptography experts to specify the secure usage of the cryptographic libraries they provide. We have implemented a compiler that translates such CrySL specification into a context-sensitive and flow-sensitive demand-driven static analysis. The analysis then helps developers by automatically checking a given Java or Android app for compliance with the CrySL-encoded rules. We have designed an extensive CrySL rule set for the Java Cryptography Architecture (JCA), and empirically evaluated it by analyzing 10,000 current Android apps and all 204,788 current Java software artefacts on Maven Central. Our results show that misuse of cryptographic APIs is still widespread, with 95 percent of apps and 63 percent of Maven artefacts containing at least one misuse. Our easily extensible CrySL rule set covers more violations than previous special-purpose tools that contain hard-coded rules, while still offering a more precise analysis.