*00:17*[Pub][ePrint] FROPUF: How to Extract More Entropy from Two Ring Oscillators in FPGA-Based PUFs, by Qinglong Zhang and Zongbin Liu and and Cunqing Ma and Changting Li and Jiwu Jing

Ring oscillator (RO) based physically unclonable function

(PUF) on FPGAs is crucial and popular for its nice properties and easy

implementation. The compensated measurement based on the ratio of

two ring oscillators\' frequencies proves to be particularly effective to extract

entropy of process variations. However from two ring oscillators

only one bit entropy is extracted and RO PUFs will occupy numerous

resource with the size of private information increasing. Motivated by this

inefficient resource usage, we propose an elegant and efficient method to

extract at least 31 bits entropy from two ring oscillators on FPGAs by

utilizing the fine control of programmable delay lines (PDL). We call this

construction Further ROPUF (FROPUF). In this paper, we present in

detail how to take advantage of the underlying random process variation

which derives from the lookup tables (LUT) of two ring oscillators,

and show that the in-depth variation can be extracted by a similar second

order difference calculation. In addition, we reveal the consistency

of the evaluation results from Xilinx FPGAs (e.g. Virtex-5, Virtex-6,

Kintex-7) and those by simulation of FROPUF. The responses of our

new construction have a nominal bit-error-rate (BER) of 1.85% at 27

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C

and FROPUF greatly promotes the number of entropy with equivalent

reliability of the general ROPUF.