TitanSSL: Towards Accelerating OpenSSL in a Full RISC-V Architecture Using OpenTitan Root-of-Trust

RISC-V open-hardware designs are emerging in cyber-physical systems and security-critical embedded platforms. Among them, OpenTitan emerged as an open-source silicon Root-of-Trust, which provides secure-boot and execution-integrity functionalities, exploiting its internal hardware accelerators. In this paper, we explore a novel exploitation of OpenTitan as a secure cryptographic accelerator. To this purpose, we designed TitanSSL, a secure software stack that offloads cryptographic tasks to OpenTitan, and we study the trade-offs between offloading overhead through the stack and the obtained computation speed-up. TitanSSL includes an OpenSSL backend, a Linux driver for communications, and an OpenTitan firmware. We executed TitanSSL on a cycle-accurate simulator of a RISC-V CVA6 application processor integrated with OpenTitan on the same System-on-Chip. We compared our implementation with a pure software version across different cryptographic payloads. Finally, we provide guidelines for the use of OpenTitan as a coprocessor in secure cyber-physical systems designs based on open-hardware architectures.