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Nov 14, 2022 115 likes •340 views

CRYPTARCHI 2017 Smolenice "Formalism to Assess the Entropy and Reliability of Loop PUF" Jean-Luc Danger 1,2 Olivier Rioul 1 Sylvain Guilley 1,2 Alexander Schaub 1 1 Tlcom ParisTech, LTCI, UPSAY 2 Secure-IC Page 1

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Jean-Luc Danger CRYPTARCHI 2017

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Télécom-ParisTech

CRYPTARCHI 2017 Smolenice "Formalism to Assess the Entropy and Reliability of Loop PUF"

Jean-Luc Danger1,2 Olivier Rioul1 Sylvain Guilley1,2 Alexander Schaub1

1 Télécom ParisTech, LTCI, UPSAY 2 Secure-IC

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Outline

 Loop PUF architecture  Entropy assessment  Reliability assessment  Results on real silicon  Conclusions

* Depends on algorithm, not implementation

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Loop PUF architecture

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Operating Mode

The information for each challenge is D Sign = identifier Module = reliability

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Balance of Delay Elements in ASIC

duplication

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Balance of Delay Elements in FPGA

Cluster 1 Cluster N Cluster 2 duplication N duplications

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Delay measurement

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Entropy

 For a n-delay LPUF

If challenge = Hadamard codeword of n bits => Entropy = n *

* Rioul, O., Solé, P ., Guilley, S., & Danger, J. L. (2016, July). On the Entropy of Physically Unclonable

Functions. In Information Theory (ISIT), 2016 IEEE International Symposium on (pp. 2928-2932).

IEEE.

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Entropy with more than n challenges

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LPUF reliability

With

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LPUF reliability

The Reliability is not enough ~10-3 even with high SNR => Needs of secure sketch : Error Correcting codes and Helper data

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Reliability enhancement by delay knowledge

The bits in the unreliable area "B" are discarded The helper data indicates the unreliable bits

Bit unreliable  |delay| < Th Th= Ws

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New BER with filtered bits

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Entropy after bit filtering

Number of delay elements to reach n bits of entropy with Hadamard codes

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Results on real silicon

 n=54 cells, 65nm technology

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i..i.d. check

No correlation between the 64 delay elements => entropy ~ 64 with Hadamard codes Correlation matrix on the 64 elements of the 49 PUFs

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Impact of the measurement window on the SNR

SNR ~60 for log2L=14

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Entropy

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Reliability: BER results

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Conclusions

 The Entropy of the Loop PUF can be formally obtained if Hadamard codes are used:

Entropy = number of delay elements n
The entropy increases non linearly if M > n

 The reliability of the Loop PUF is low (BER ~10-3)  It can be easily improved by exploiting the delay knowledge

The unreliable bits are discarded
BER can go down 10-9
But more bits are needed to reach the same entropy

N=Number of challenges

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CRYPTARCHI 2017 Smolenice "Formalism to Assess the Entropy and Reliability of Loop PUF"

Outline

Loop PUF architecture

Operating Mode

Balance of Delay Elements in ASIC

Balance of Delay Elements in FPGA

Delay measurement

Entropy

Entropy with more than n challenges

LPUF reliability

LPUF reliability

Reliability enhancement by delay knowledge

New BER with filtered bits

Entropy after bit filtering

Results on real silicon

i..i.d. check

Impact of the measurement window on the SNR

Entropy

Reliability: BER results

Conclusions

THANK YOU FOR YOUR ATTENTION