FSM merging and reduction for IP cores watermarking using Genetic Algorithms

This paper proposes an improved procedure to watermark soft Intellectual Property (IP) Cores at the Register Transfer Level (RTL) using Genetic Algorithms (GA). In order to merge the watermark signature and the IP Core´s behavioral description, both are translated into Finite State Machines (FSM). The resulting FSM contains the watermarked IP Core maintaining its original functionality without disruption. However, a set of hanging states (a group of states not deeply embedded) has been observed and if any of these is deleted, the watermark could be removed and possibly the original IP Core functionality would not be disrupted, allowing for copyright infringements. Thus, a reduction procedure is applied to the watermarked design to reduce the number of hanging states, which to the best of the authors´ knowledge has not been developed. Both FSM merging and reduction are NP-Complete problems. In this study, an improved objective function is proposed to accurately model the FSM reduction problem while applying GAs as optimization techniques at both stages. Empirical results show a significant improvement in terms of the number of final hanging states and watermark embedding strength as regards previous reported approaches.