Capacitive PUF Circuit Using Reference Comparison for Secure Keys
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Solution Overview
Problem
Existing integrated physical unclonable function (PUF) devices using ring oscillator circuits are not robust due to the vulnerability of capacitance measurement, allowing unauthorized duplication and key generation.
Innovation Solution
An integrated PUF device with a reference capacitor and comparison capacitors, a capacitance determination circuit, and a comparison circuit that generates a digital word based on capacitance comparisons, making it difficult to measure capacitances externally and thus enhancing robustness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ring oscillator circuits with large capacitors are used to generate digital words, then the oscillation frequency can be reliably determined, but the capacitance becomes measurable by external attackers enabling device duplication
Solution Approach 1:
The patent segments the capacitor functionality into two separate components: a small intrinsic capacitor integrated within the ring oscillator circuit that determines oscillation frequency, and a large extrinsic capacitor connected externally that provides measurement stability without being measurable by attackers. This segmentation allows the system to benefit from both small capacitor security and large capacitor reliability.
Solution Approach 2:
The patent introduces an intermediary measurement mechanism that compares oscillation frequencies of multiple ring oscillator circuits without requiring direct capacitance measurement. The frequency comparison serves as an intermediary that indirectly reveals device characteristics while preventing direct capacitance extraction, thus maintaining security while enabling authentication.
2Object-affected harmful factors
If small intrinsic capacitors are used in ring oscillator circuits, then capacitance measurement by attackers becomes difficult, but the oscillation frequency determination becomes less reliable
Solution Approach 1:
The patent segments the capacitor functionality into two separate components: a small intrinsic capacitor integrated within the ring oscillator circuit that determines oscillation frequency, and a large extrinsic capacitor connected externally that provides measurement stability without being measurable by attackers. This segmentation allows the system to benefit from both small capacitor security and large capacitor reliability.
3Ease of operation
If capacitance values are made measurable for verification purposes, then device authentication can be performed, but unauthorized duplication and key generation become possible
Solution Approach 1:
The patent introduces an intermediary measurement mechanism that compares oscillation frequencies of multiple ring oscillator circuits without requiring direct capacitance measurement. The frequency comparison serves as an intermediary that indirectly reveals device characteristics while preventing direct capacitance extraction, thus maintaining security while enabling authentication.
Solution Approach 2:
The patent replaces direct capacitance measurement (electrical measurement) with oscillation frequency comparison (temporal measurement). This substitution changes the measurement domain from direct electrical property measurement to indirect temporal behavior observation, maintaining authentication capability while enhancing security.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides a robust PUF device with unique digital words for each device, preventing unauthorized duplication and ensuring secure key generation.
Implementation Method 1
a capacitance determination circuit configured to determine capacitances of said at least one reference capacitor and of each comparison capacitor
Data Source
AI summary
An integrated physical unclonable function device includes at least one reference capacitor and a number of comparison capacitors. A capacitance determination circuit operates to determine a capacitance of the at least one reference capacitor and a capacitance of each comparison capacitor. The determined capacitances of the comparison capacitors are then compared to the determined capacitance of the reference capacitor by a comparison circuit. A digital word is then generated with bit values indicative of a result of the comparisons made by the comparison circuit.