VLSI Design of a Large-Number Multiplier for Fully Homomorphic Encryption

This paper presents the design of a power- and area-efficient high-speed 768000-bit multiplier, based on fast Fourier transform multiplication for fully homomorphic encryption operations. A memory-based in-place architecture is presented for the FFT processor that performs 64000-point finite-field FFT operations using a radix-16 computing unit and 16 dual-port SRAMs. By adopting a special prime as the base of the finite field, the radix-16 calculations are simplified to requiring only additions and shift operations. A two-stage carry-look-ahead scheme is employed to resolve carries and obtain the multiplication result. The multiplier design is validated by comparing its results with the GNU Multiple Precision (GMP) arithmetic library. The proposed design has been synthesized using 90-nm process technology with an estimated die area of 45.3 mm². At 200 MHz, the large-number multiplier offers roughly twice the performance of a previous implementation on an NVIDIA C2050 graphics processor unit and is 29 times faster than the Xeon X5650 CPU, while at the same time consuming a modest 0.97 W.