Co-Embedding Additional Security Data and Obfuscating Low-Level FPGA Program Code

The paper is devoted to the issues of equivalent transformation of the FPGA program code in order to protect the integrity of this code. The paper considers an approach in which a digital watermark is covertly embedding into the FPGA program code. This digital watermark contains the monitoring data needed to implement the code integrity monitoring procedure. As a result, the digital watermark is hidden in the program code and forms a single whole with the program code. The embedded digital watermark does not change the characteristics of the device and does not make changes to its operation. Due to this approach, the fact of performing integrity monitoring in relation to program code is not obvious to an external observer. At the same time, monitoring data is also hidden and inaccessible. The paper proposes a method that improves integrity monitoring by jointly perform two processes: embedding secret additional data into the FPGA program code and obfuscating this program code. Moreover, both of these processes are proposed to be performed using one common system of equivalent transformations for the elementary units of the FPGA program code. Improved integrity monitoring is seen in the fact that the probability of detecting a digital watermark in FPGA program code is reduced. The paper describes an experiment showing the advantage of the proposed method over existing methods. The paper also provides recommendations on the possibility of using the method in areas that are related to the task of monitoring the integrity for FPGA program code.