  Authorship attribution has become increasingly accurate, posing a serious
privacy risk for programmers who wish to remain anonymous. In this paper, we
introduce SHIELD to examine the robustness of different code authorship
attribution approaches against adversarial code examples. We define four
attacks on attribution techniques, which include targeted and non-targeted
attacks, and realize them using adversarial code perturbation. We experiment
with a dataset of 200 programmers from the Google Code Jam competition to
validate our methods targeting six state-of-the-art authorship attribution
methods that adopt a variety of techniques for extracting authorship traits
from source-code, including RNN, CNN, and code stylometry. Our experiments
demonstrate the vulnerability of current authorship attribution methods against
adversarial attacks. For the non-targeted attack, our experiments demonstrate
the vulnerability of current authorship attribution methods against the attack
with an attack success rate exceeds 98.5\% accompanied by a degradation of the
identification confidence that exceeds 13\%. For the targeted attacks, we show
the possibility of impersonating a programmer using targeted-adversarial
perturbations with a success rate ranging from 66\% to 88\% for different
authorship attribution techniques under several adversarial scenarios.
