Bus-Keeper PUF Circuit for Stable Low-Power Identifier Readout
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Solution Overview
Problem
Physical unclonable functions (PUFs) face challenges in maintaining consistent digital identifiers across power cycles due to manufacturing variations, leading to errors and the need for error correction, while also requiring efficient power management to reduce aging effects and component size.
Innovation Solution
A PUF system comprising bus-keepers that settle into stable states based on random physical characteristics, utilizing a reading circuit with multiplexers for selection and a power domain for controlled power supply, allowing for read-only operations and reduced power consumption, which enables multiple power-up and read cycles to average and reduce noise in the identifier derivation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If error correction procedures using helper data are implemented to correct manufacturing variations, then digital identifier consistency across power cycles is improved, but device complexity and memory requirements increase
Solution Approach 1:
The patent performs error correction and derives the digital identifier during the power-up sequence before the device is fully operational. By preliminarily correcting errors using stored helper data and applying XOR operations with challenge values, the system ensures identifier consistency without requiring complex runtime error correction mechanisms.
Solution Approach 2:
The PUF system uses its own internal structure (bus-keepers and their startup states) to generate and verify identifiers. The helper data stored in the device enables self-correction of manufacturing variations, and the system automatically derives consistent identifiers through deterministic processing of the bus-keeper states without external intervention.
2Reliability
If continuous power supply is provided to maintain stable operation, then operational reliability is improved, but aging effects and power consumption increase
Solution Approach 1:
The patent implements periodic power cycling of the bus-keepers, where power is supplied only during identifier derivation operations. The bus-keepers are powered up, their states are read and processed to generate the digital identifier, then power is removed. This periodic operation maintains operational reliability when needed while minimizing continuous power consumption and reducing aging effects from constant power exposure.
3Adaptability or versatility
If write logic and address decoders are included for full memory functionality, then memory versatility is improved, but device complexity and component size increase
Solution Approach 1:
The patent extracts only the essential read functionality from full memory operations. Write logic, address decoders, and other complex memory control circuits are removed, leaving only the bus-keepers for storage and a simple reading circuit for retrieval. This extraction maintains the core PUF functionality of storing and reading challenge-response pairs while dramatically reducing device complexity and component count.
4Measurement precision
If multiple power-up and read cycles are performed to average noise, then measurement precision is improved, but time consumption increases
Solution Approach 1:
The patent performs a limited number of power-up and read cycles (typically 2-5 times) to average noise, rather than exhaustive multiple cycles. This partial action achieves sufficient measurement precision for cryptographic applications while constraining time consumption. The system balances the diminishing returns of additional averaging against the linear increase in processing time, selecting an optimal number of cycles that provides adequate precision without excessive time cost.
Data Source
AI summary
A physical unclonable function is provided 100, comprising a plurality of bus-keepers 110, each bus-keeper of the plurality of bus-keepers 110 being configured to settle into one of at least two different stable states upon power-up, the particular stable state into which a particular bus-keeper of the plurality of bus-keepers settles being dependent at least in part upon the at least partially random physical characteristics of the particular bus-keeper, and a reading circuit 120 for reading the plurality of stable states into which the plurality of bus-keepers settled after a power-up, the plurality of bus-keepers being read-only.