On Entropy and Bit Patterns of Ring Oscillator Jitter
This work provides improved methods for evaluating the entropy of ring oscillator-based True Random Number Generators, which is crucial for compliance with standards like NIST 800-90B and AIS-31 for security and cryptographic applications.
This paper addresses the evaluation of entropy, autocorrelation, and bit pattern distributions of thermal jitter from ring oscillators, which are used as physical randomness sources. The authors developed numerical evaluation algorithms that are faster and more accurate than Monte Carlo simulations and proposed a new, more general lower bound estimation formula for ring oscillator entropy.
Thermal jitter (phase noise) from a free-running ring oscillator is a common, easily implementable physical randomness source in True Random Number Generators (TRNGs). We show how to evaluate entropy, autocorrelation, and bit pattern distributions of ring oscillator noise sources, even with low jitter levels or some bias. Entropy justification is required in NIST 800-90B and AIS-31 testing and for applications such as the RISC-V entropy source extension. Our numerical evaluation algorithms outperform Monte Carlo simulations in speed and accuracy. We also propose a new lower bound estimation formula for the entropy of ring oscillator sources which applies more generally than previous ones.