Low-Complexity VLSI Design of Large Integer Multipliers for Fully Homomorphic Encryption

Large integer multiplication has been widely used in fully homomorphic encryption (FHE). Implementing feasible large integer multiplication hardware is thus critical for accelerating the FHE evaluation process. In this paper, a novel and efficient operand reduction scheme is proposed to reduce the area requirement of radix-r butterfly units. We also extend the single-port, merged-bank memory structure to the design of number theoretic transform (NTT) and inverse NTT (INTT) for further area minimization. In addition, an efficient memory addressing scheme is developed to support both NTT/INTT and resolving carries computations. Experimental results reveal that significant area reductions can be achieved for the targeted 786432-and 1179648-bit NTT-based multipliers designed using the proposed schemes in comparison with the related works. Moreover, the two multiplications can be accomplished in 0.196 and 2.21 ms, respectively, based on 90-nm CMOS technology. The low-complexity feature of the proposed large integer multiplier designs is thus obtained without sacrificing the time performance.