PUF Response Generator Circuit Reliability Optimization
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Solution Overview
Problem
Physical unclonable function (PUF) circuits generate unreliable random bits due to environmental variations and device aging, which can lead to inconsistent responses, especially when small electrical differences are amplified, affecting applications like device identification and secret key generation that require reliability.
Innovation Solution
A method and system that utilize a built-in self-test (BIST) circuit to generate reliability information for each bit of a PUF array, selecting and aggregating only the reliable bits based on this information to produce a more consistent PUF response, which is then used as a cryptographic key, employing a sense amplifier-based PUF array and non-volatile memory for storage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If small electrical differences are amplified to generate PUF bits, then the PUF can operate with smaller device variations, but the reliability of PUF response bits deteriorates due to polarity flipping across environmental variations
Solution Approach 1:
The system performs preliminary characterization during manufacturing to measure the offset voltage of each sense amplifier and classify them into reliable and unreliable groups. This pre-screening allows the system to identify which PUF bits will maintain consistent polarity across environmental variations, enabling reliable operation with small device variations.
Solution Approach 2:
The patent applies different treatment to different PUF bits based on their individual characteristics. By measuring and classifying each sense amplifier's offset voltage, the system identifies locally reliable bits (those with sufficient offset margin) and excludes unreliable bits, rather than treating all PUF bits uniformly. This selective approach maintains reliability while allowing small device variations.
2Reliability
If larger electrical differences are amplified, then PUF bit reliability improves, but larger device variations are required which increases manufacturing complexity
Solution Approach 1:
The system changes the operational parameter by measuring and utilizing the offset voltage characteristic of each sense amplifier. By selecting PUF bits where the offset voltage exceeds a threshold margin, the system ensures reliable polarity retention without requiring larger device variations. The parameter change from uniform amplification to selective amplification based on measured characteristics resolves the contradiction.
3Productivity
If all PUF bits are used to generate responses, then the response generation is simple and fast, but error rate increases due to unreliable bits from environmental variations
Solution Approach 1:
The system performs preliminary classification of PUF bits during manufacturing, storing reliability information for each bit. During operation, this pre-stored information enables rapid selection of only reliable bits, maintaining fast response generation while eliminating unreliable bits that would cause errors. The preliminary action of classification resolves the contradiction between speed and accuracy.
Solution Approach 2:
The patent extracts and removes unreliable PUF bits from the response generation process. By identifying bits where the offset voltage margin is insufficient and excluding them from active use, the system reduces the total number of usable PUF bits but ensures that only reliable bits contribute to the response. This extraction of harmful elements (unreliable bits) improves accuracy while maintaining acceptable speed.
4Object-affected harmful factors
If PUF responses are used for cryptographic key generation, then security is enhanced against attacks, but reliability must be perfect which is not achieved with current PUF implementations
Solution Approach 1:
The patent applies local quality assessment to each PUF bit by measuring its offset voltage and determining its reliability individually. This per-bit quality assessment enables the system to identify and use only those bits with sufficient stability margin, ensuring perfect reliability for cryptographic applications. The local differentiation of bit quality resolves the contradiction between security requirements and actual reliability.
Data Source
AI summary
In some aspects, a method includes obtaining, by a response generator circuit, reliability information for each bit of an array of bits provided by a physical unclonable function (PUF) circuit; receiving, from the PUF circuit during run time, an array of values for the array of bits; selecting a plurality of values from the array of values received from the PUF circuit in accordance with the reliability information; and generating, by the response generator circuit, a PUF response from the selected plurality of values.