Cryptology ePrint Archive: Report 2021/1363

On Entropy and Bit Patterns of Ring Oscillator Jitter

Markku-Juhani O. Saarinen

Abstract: 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.

Category / Keywords: implementation / Entropy Source, Ring Oscillator, TRNG, FIPS 140-3, SP 800-90B, AIS-31

Original Publication (with minor differences): IEEE AsianHOST 2021

Date: received 10 Oct 2021, last revised 12 Oct 2021

Contact author: mjos at mjos fi

Available format(s): PDF | BibTeX Citation

Note: There is supplementary code available at:

Version: 20211012:151207 (All versions of this report)

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