PUF Key Bit Stability via Mismatch Threshold Pairing
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Solution Overview
Problem
Existing PUF systems face challenges in achieving high utilization rates without compromising the stability and accuracy of generated key bits due to environmental and process variations, leading to unstable crypto keys.
Innovation Solution
The method involves individually measuring mismatch values of PUF elements, pairing them to ensure a sufficient difference, and using a dedicated selection circuit to transform the statistical distribution, thereby generating stable PUF key bits that are insensitive to errors caused by environmental variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If PUF elements with small mismatch values are excluded to improve stability, then key bit stability improves, but utilization rate decreases
Solution Approach 1:
The patent applies preliminary action by pre-characterizing PUF elements during manufacturing to identify and exclude those with small mismatch values before they are used in cryptographic operations. This advance sorting ensures that only elements with sufficient mismatch (greater than a threshold) are selected for key generation, preventing future instability without needing to exclude elements during operation.
Solution Approach 2:
The patent changes the parameter selection criterion from using all PUF elements to selectively using only those with mismatch values exceeding a predetermined threshold. This parameter-based filtering transforms the utilization approach from inclusive to selective, ensuring stability while maximizing the number of usable elements that meet the criterion.
2Productivity
If PUF elements with small mismatch are used to increase utilization, then utilization rate improves, but key bit stability deteriorates
Solution Approach 1:
The patent implements a minimum mismatch threshold parameter that filters out elements with small mismatch values. By setting this parameter (threshold > 0), the system automatically excludes unstable elements while including all elements that meet the criterion, thereby achieving both high utilization and stability simultaneously.
Solution Approach 2:
The patent incorporates feedback through the characterization process where mismatch values are measured and compared against the threshold criterion. Elements are sorted based on this feedback, and only those satisfying the condition (mismatch > threshold) are selected for key generation, creating a closed-loop quality assurance mechanism.
3Device complexity
If environmental variations are not compensated, then system complexity remains low, but measurement precision deteriorates
Solution Approach 1:
The patent applies preliminary characterization during manufacturing to identify and exclude PUF elements sensitive to environmental variations. By pre-screening elements with small mismatch values that are prone to environmental influence, the system prevents measurement precision deterioration without requiring complex real-time compensation mechanisms during operation.
Data Source
AI summary
Various embodiments of the invention allow to take advantage of the natural statistical variation of physical properties in a semiconductor device in order to create truly random, repeatable, and hard to detect cryptographic bits. In certain embodiments, this is accomplished by pairing mismatch values of PUF elements so as to ensure that PUF key bits generated thereform remain insensitive to environmental errors, without affecting the utilization rate of available PUF elements.