PUF Response Bit Selection for Stable High-Entropy Output
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Solution Overview
Problem
Existing PUF technologies face challenges in maintaining stability while maximizing entropy, leading to reduced security due to imbalanced '0' and '1' distributions, making them vulnerable to attacker predictions.
Innovation Solution
A method for generating PUF responses by discarding output bits where |υ - T| < δυ + |T| or |υ + T| < δυ, ensuring symmetrical '0' and '1' counts and maximizing entropy through a symmetrical selection process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If bit selection methods are used to ensure PUF output stability, then stability is improved, but entropy is reduced
Solution Approach 1:
The patent changes the selection parameter from a fixed threshold (comparing against 0.5) to a dynamic threshold based on the comparator offset T. By selecting bits where |υ - T| > δυ, the selection criterion adapts to the comparator's inherent offset, maintaining stability while preserving entropy. This parameter change allows the system to account for the non-zero offset without discarding valuable high-entropy bits.
2Reliability
If a non-zero comparator offset T is used, then stability is improved, but entropy is reduced due to imbalance between 0 and 1 outputs
Solution Approach 1:
The patent introduces asymmetry in the selection process by using the offset T itself as part of the selection criterion. Instead of treating all bits equally or using a symmetric threshold around zero, the method selectively keeps bits where the difference |υ - T| exceeds δυ. This asymmetric selection compensates for the offset-induced imbalance, restoring entropy while maintaining the stability benefits of the non-zero offset.
3Reliability
If existing bit selection methods are used, then output stability is improved, but security is weakened due to predictable bit distributions
Solution Approach 1:
By changing the selection parameter from a fixed zero-centered threshold to an offset-aware threshold |υ - T| > δυ, the patent prevents attackers from predicting bit distributions. The dynamic threshold adapts to each comparator's characteristics, making it impossible for attackers to use statistical models based on fixed thresholds to predict PUF outputs, thereby maintaining security while ensuring stability.
Data Source
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AI summary
The present invention relates to a method for generating a physical unclonable function (PUF) response by a PUF circuit of an electronic device, said PUF circuit comprising pairs of electronic components called PUF primitives implementing said physical unclonable function and, for each PUF primitives pair, a comparator having as inputs electrical characteristic values of the PUF primitives of said PUF primitive pair, and configured for generating an analog differential value υ - T with υ a difference between said electrical characteristic values and T a non-zero current offset of said comparator, performing an analog to digital conversion of said analog differential value υ - T, and outputting a PUF output bit equal to the result of said analog to digital conversion, said method comprising : - obtaining (S1) a challenge, - generating (S2) PUF output bits by applying said physical unclonable function to said obtained challenge, - generating (S3) said PUF response from said generated PUF output bits verifying υ > δυ +|Τ| or υ < -δυ −|Τ| with δυ a predetermined threshold.