Practical feasibility evaluation and improvement of a pay-per-use licensing scheme for hardware IP cores in Xilinx FPGAs

In earlier published work, Maes et al. present a pay-per-use licensing scheme for hardware Intellectual Property (IP) cores. This scheme focuses on the use of IP cores on static random access memory-based field programmable gate arrays (FPGAs) and is mainly based on the partial reconfigurability property of this type of FPGA. Our work evaluates the practical feasibility of the scheme and the accompanying architecture. As already (partly) indicated by Maes et al., their solution introduces some security and usability issues. Therefore, we present improvements to the scheme and the architecture together with an additional method for decreasing the area overhead. The overall result is the first practical implementation of the pay-per-use licensing scheme occupying 841 slices on a Xilinx XC6S-LX45 FPGA. The small area overhead is mainly achieved by moving the storage of keys from slice flip-flops to configuration memory. Moreover, the implementation would not have been feasible with commercially available tools. We use an academic tool that allows nested partial reconfiguration and flexible IP core placement.