Security and Complexity Analysis of LUT-based Obfuscation: From Blueprint to Reality

Recent obfuscation schemes have leveraged reconfigurable logics to alleviate various hardware security threats. However, existing reconfigurable logic-based obfuscation schemes focus on specific design factors such as gate replacement strategy or an optimization metric such as SAT-hardness. Despite meeting the focused metrics such as security, the obfuscation also incurs overheads, which are not well analyzed in the existing works. In this work, we provide a comprehensive analysis on reconfigurable logic obfuscation schemes i.e., LUT-based obfuscation by investigating 3-key design factors such as (1) LUT size, (2) number of LUTs, and (3) replacement strategy as they have a considerable impact on design criteria, i.e., Power-Performance-Area (PPA) and Security (PPA/S). Our results show that among the studied parameters the size of LUT has the most prominent impact on improving the resiliency of LUT-based obfuscation against the SAT and removal attacks. However, using large size LUTs incur significant PPA overheads, making such solutions unfeasible and unpractical. To address this challenge, this work proposes a pragmatic solution based on a customized LUT, where the security provided by each LUT is superior to that of traditional LUT-based obfuscation. The proposed solution primarily benefits from LUT-based obfuscation reinforced with additional logic/routing obfuscation that is implemented using small 2-input LUTs. We evaluate the hardware security and overhead of the proposed customized LUT-based obfuscation on various benchmarks to prove that the customized LUT-based obfuscation breaks the PPA tradeoffs while exhibiting robustness against the SAT and removal attacks. The customized LUT-based obfuscation comes with 8× reduced area and 2× reduced power on an average compared to state-of-the-art LUT-based obfuscation without compromising security.