Stefan Krüger

Mohammadreza Hazhirpasand, Mohammad Ghafari, Stefan Krüger et al.

Previous research has shown that crypto APIs are hard for developers to understand and difficult for them to use. They consequently rely on unvalidated boilerplate code from online resources where security vulnerabilities are common. We analyzed 2,324 open-source Java projects that rely on Java Cryptography Architecture (JCA) to understand how crypto APIs are used in practice, and what factors account for the performance of developers in using these APIs. We found that, in general, the experience of developers in using JCA does not correlate with their performance. In particular, none of the factors such as the number or frequency of committed lines of code, the number of JCA APIs developers use, or the number of projects they are involved in correlate with developer performance in this domain. We call for qualitative studies to shed light on the reasons underlying the success of developers who are expert in using cryptography. Also, detailed investigation at API level is necessary to further clarify a developer obstacles in this domain.

Rodrigo Bonifacio, Stefan Krüger, Krishna Narasimhan et al.

APIs are the primary mechanism for developers to gain access to externally defined services and tools. However, previous research has revealed API misuses that violate the contract of APIs to be prevalent. Such misuses can have harmful consequences, especially in the context of cryptographic libraries. Various API misuse detectors have been proposed to address this issue including CogniCrypt, one of the most versatile of such detectors and that uses a language CrySL to specify cryptographic API usage contracts. Nonetheless, existing approaches to detect API misuse had not been designed for systematic reuse, ignoring the fact that different versions of a library, different versions of a platform, and different recommendations or guidelines might introduce variability in the correct usage of an API. Yet, little is known about how such variability impacts the specification of the correct API usage. This paper investigates this question by analyzing the impact of various sources of variability on widely used Java cryptographic libraries including JCA, Bouncy Castle, and Google Tink. The results of our investigation show that sources of variability like new versions of the API and security standards significantly impact the specifications. We then use the insights gained from our investigation to motivate an extension to the CrySL language named MetaCrySL, which builds on meta programming concepts. We evaluate MetaCrySL by specifying usage rules for a family of Android versions and illustrate that MetaCrySL can model all forms of variability we identified and drastically reduce the size of a family of specifications for the correct usage of cryptographic APIs

Lisa Nguyen Quang Do, Stefan Krüger, Patrick Hill et al.

To detect and fix bugs and security vulnerabilities, software companies use static analysis as part of the development process. However, static analysis code itself is also prone to bugs. To ensure a consistent level of precision, as analyzed programs grow more complex, a static analysis has to handle more code constructs, frameworks, and libraries that the programs use. While more complex analyses are written and used in production systems every day, the cost of debugging and fixing them also increases tremendously. To better understand the difficulties of debugging static analyses, we surveyed 115 static analysis writers. From their responses, we extracted the core requirements to build a debugger for static analysis, which revolve around two main issues: (1) abstracting from two code bases at the same time (the analysis code and the analyzed code) and (2) tracking the analysis internal state throughout both code bases. Most current debugging tools that our survey participants use lack the capabilities to address both issues. Focusing on those requirements, we introduce VisuFlow, a debugging environment for static data-flow analysis that is integrated in the Eclipse development environment. VisuFlow features graph visualizations that enable users to view the state of a data-flow analysis and its intermediate results at any time. Special breakpoints in VisuFlow help users step through the analysis code and the analyzed simultaneously. To evaluate the usefulness of VisuFlow, we have conducted a user study on 20 static analysis writers. Using VisuFlow helped our sample of analysis writers identify 25% and fix 50% more errors in the analysis code compared to using the standard Eclipse debugging environment.

Stefan Krüger, Johannes Späth, Karim Ali et al.

Various studies have empirically shown that the majority of Java and Android apps misuse cryptographic libraries, causing devastating breaches of data security. Therefore, it is crucial to detect such misuses early in the development process. The fact that insecure usages are not the exception but the norm precludes approaches based on property inference and anomaly detection. In this paper, we present CrySL, a definition language that enables cryptography experts to specify the secure usage of the cryptographic libraries that they provide. CrySL combines the generic concepts of method-call sequences and data-flow constraints with domain-specific constraints related to cryptographic algorithms and their parameters. We have implemented a compiler that translates a CrySL ruleset into a context- and flow-sensitive demand-driven static analysis. The analysis automatically checks a given Java or Android app for violations of the CrySL-encoded rules. We empirically evaluated our ruleset through analyzing 10,001 Android apps. Our results show that misuse of cryptographic APIs is still widespread, with 96% of apps containing at least one misuse. However, we observed fewer of the misuses that were reported in previous work.