Reconfigurable multi-core array architecture and mapping method for RNS-based homomophic encryption

Fully homomorphic encryption (FHE) plays a vital role in privacy-preserving outsourcing computing and cloud computing security. However, efficiency is still the main factor limiting the actual use of FHE. This paper presents an area-efficient reconfigurable multi-core array architecture (named RMCA) and mapping method for the RNS variant of CKKS scheme. To accelerate the time-consuming polynomial multiplication, we present an improved NTT/INTT algorithm without pre/post-processing and a reconfigurable processing element (PE) unit that can be configured as NTT, INTT and modular multiplier. Also, a memory-saving NTT architecture and memory organization of the twiddle factor are introduced to reduce the data and twiddle factor memory overhead by 25 % and 50 %, respectively. Furthermore, targeting the computational requirements of RNS-CKKS, a unified computational model and distributed on-chip memory organization are presented for RMCA. Lastly, all the computational units involved in the homomorphic evaluation of RNS-CKKS are optimized and mapped on RMCA reasonably. When evaluated on Virtex UltraScale XCVU190 FPGA at 300 MHz, RMCA can perform 9154, 4308 and 1743 homomorphic multiplications per second for N = 4096, 8192 and 16384, respectively, and the area-time-products (ATPs) are improved by 1.11×∼8.60 × for a wide range of parameter sets.