Cryptology ePrint Archive: Report 2019/810

Refutation and Redesign of a Physical Model of TERO-based TRNGs and PUFs

Jeroen Delvaux

Abstract: In an article from CHES 2015, which appears in extended form in the Journal of Cryptology in 2019, Bernard, Haddad, Fischer, and Nicolai modeled the physical behavior of a transient effect ring oscillator (TERO), thereby providing a means to certify its operation as a true random number generator (TRNG). In this work, we disprove the physical assumption on which the whole model is based. Moreover, we show that the convenient use of tractable, closed-form equations stems from a mathematical error. On a more constructive note, we are the first to point out that TEROs and Bistable Ring physically unclonable functions (PUFs) are closely related, thereby not only laying the foundations of a more accurate physical model but also revealing a new design trade-off between throughput, entropy, and reliability. Furthermore, we demonstrate that most TERO implementations in the literature are prone to counter value corruptions, and propose a solution to this problem. Measurements performed on a field-programmable gate array (FPGA) substantiate our claims.

Category / Keywords: implementation / transient effect ring oscillator, true random number generator, physically unclonable function, stochastic model

Date: received 11 Jul 2019

Contact author: jeroen delvaux at osr-tech com

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Version: 20190714:155609 (All versions of this report)

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