RISC-V Extension for Lightweight Cryptography

Lightweight Cryptography (LWC) is suitable for IoTs which require a high level of security while keeping a low complexity. Many lightweight cryptographic algorithms have been proposed to satisfy these requirements. But there is currently no emerging standard concerning the symmetric block ciphering, as every algorithm has its own advantage. For instance one can be optimized for low latency, another one for low complexity but requires more rounds to be cryptographically secure to the detriment of throughput. Hence, a processor able to cope with all the algorithms should be ideal to provide agility, performance and security while keeping an affordable complexity. We present in this paper a specific execution unit of the RISC-V processor which is able to run the most common lightweight 64-bit block ciphers. The gain in performance can reach over a hundred compared to the reference architecture. The acceleration takes advantage of five specific instructions which can easily be adapted to the execution unit of a VexRiscv architecture. The complexity can double when implementing the new execution unit, but provide a high degree of agility and performance when executing most of lightweight cryptographic implementations.