Temporally Robust Software Features for Authorship Attribution

Authorship attribution is used to determine the creator of works among many candidates, playing a vital role in software forensics, authorship disputes and academic integrity investigations. The evolving coding style of individuals may degrade the performance of systems that attribute authorship of source code, and has not been previously studied. This paper uses a collection of six programming assignments with guaranteed relative timestamps from 272 students to examine evolution of coding style. We find that the problem domain of the software developed has a large affect on the ability to attribute authorship, and that coding style does change over time regardless of the requirements that are coded. The outcomes suggest that it takes at least three programming tasks for coding style to settle, and that at least one piece of code in the same problem domain as the code to classify is necessary for accurate authorship attribution. In the final part of the paper we analyze low level code features to discover simple features that appear immune to evolution of coding style, and use them to improve effectiveness of our system from 79% to 82% (p < 0.01, z-test).