RISC-V Global Forum 2020

Crypto Task Group's proposed RISC-V True Random Number Generator (TRNG) architecture breaks with previous ISA TRNG practice by splitting the Entropy Source (ES) component away from cryptographic PRNGs into a separate interface, and in its use of polling. We describe the interface, its use in cryptography, and the rationale behind its engineering choices. This design is informed by lessons learned from earlier mainstream ISAs, recently introduced SP 800-90B and FIPS 140-3 entropy audit requirements, AIS 31 and Common Criteria, current and emerging cryptographic needs such as post-quantum cryptography. We also introduce Minidice, a minimalistic TRNG reference implementation that uses the Entropy Source together with RISC-V AES instructions.