An obfuscated radix-2 real FFT architecture

Design of integrated circuits that cannot be reverse engineered is very important for protecting the intellectual property of owners. Integrated circuits can be obfuscated by introducing several modes into the control flow. Only one of the modes is the desired mode and other modes represent either meaningful modes where computations are partially correct or modes where the outputs computed are completely random. This paper presents a novel architecture and implementation of an obfuscated FFT for real input signals. The proposed design can be reconfigured to compute real FFTs of size N or N/4 with 2-parallel or 4-parallel processing, which are considered the 4 meaningful modes in the design. A 4-bit configure data is used to select one of the four meaningful modes. The remaining 12 modes output partially correct results. The meaningful mode with the most number of blocks, i.e., an N-point, 4-parallel real FFT, is designed first and that circuit is then obfuscated with the inclusion of a reconfigurator and an obfuscating FSM. A novel control flow approach is introduced for hiding the modes for obfuscation. It is shown that the proposed approach results in minimal area and power overhead compared to the base design.