Control-flow Flattening Preserves the Constant-Time Policy (Extended Version)

Abstract

Obfuscating compilers protect a software by obscuring its meaning and impeding the reconstruction of its original source code. The typical concern when defining such compilers is their robustness against reverse engineering and the performance of the produced code. Little work has been done in studying whether the security properties of a program are preserved under obfuscation. In this paper we start addressing this problem: we consider control-flow flattening, a popular obfuscation technique used in industrial compilers, and a specific security policy, namely constant-time. We prove that this obfuscation preserves the policy, i.e., that every program satisfying the policy still does after the transformation. * The first two authors have been partially supported by project PRA_2018_66 DECLware: Declarative methodologies for designing and deploying applications of the Università di Pisa; the third author by MIUR project PRIN 2017FTXR7S IT MATTERS (Methods and Tools for Trustworthy Smart Systems).