An Embedded RISC-V Core with Fast Modular Multiplication

Abstract

One of the biggest concerns in IoT is privacy and security. Encryption and authentication need big power budgets, which battery-operated IoT end-nodes do not have. Hardware accelerators designed for specific cryptographic operations provide little to no flexibility for future updates. Custom instruction solutions are smaller in area and provide more flexibility for new methods to be implemented. One drawback of custom instructions is that the processor has to wait for the operation to finish. Eventually, the response time of the device to real-time events gets longer. In this work, we propose a processor with an extended custom instruction for modular multiplication, which blocks the processor, typically, two cycles for any size of modular multiplication when used in Partial Execution mode. We adopted embedded and compressed extensions of RISC-V for our proof-of-concept CPU. Our design is benchmarked on recent cryptographic algorithms in the field of elliptic-curve cryptography. Our CPU with 128-bit modular multiplication operates at 136MHz on ASIC and 81MHz on FPGA. It achieves up to 13x speed up on software implementations while reducing overall power consumption by up to 95\% with 41\% average area overhead over our base architecture.