Assembly or Optimized C for Lightweight Cryptography on RISC-V?

A major challenge when applying cryptography on constrained environments is the trade-off between performance and security. In this work, we analyzed different strategies for the optimization of several candidates of NIST’s lightweight cryptography standardization project on a RISC-V architecture. In particular, we studied the general impact of optimizing symmetric-key algorithms in assembly and in plain C. Furthermore, we present optimized implementations, achieving a speed-up of up to 81% over available implementations, and discuss general implementation strategies.