SRAM PUF Security via Read Access Time Comparison
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Solution Overview
Problem
Conventional Static Random Access Memory (SRAM) Physically Unclonable Functions (PUFs) are considered weak due to limited and unsophisticated challenges, making them vulnerable to replication by attackers, and existing techniques require additional hardware or are susceptible to delayering and probing attacks.
Innovation Solution
The method involves measuring and comparing the read access times of bit cells in SRAM circuits to generate a strong PUF, using a timer or counter to determine the duration for bit cell responses, thereby increasing the number and quality of challenges, making it difficult for attackers to replicate the PUF.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional SRAM PUF techniques are used, then the implementation is simple, but the security strength is weak due to limited challenges
Solution Approach 1:
The SRAM bit cells themselves provide the timing characteristics needed for the PUF, eliminating the need for external timing measurement hardware. The inherent physical variations in bit cell read access times serve as the unique identifier, making the system self-sufficient for security purposes
Solution Approach 2:
The patent replaces conventional challenge-response PUF mechanisms with a timing-based measurement approach. Instead of using complex logical challenges and responses, the system measures the time duration of bit cell operations, substituting mechanical/logical complexity with temporal measurement simplicity
2Reliability
If additional hardware is added to strengthen PUF, then the security improves, but the device complexity increases
Solution Approach 1:
The timing measurement mechanism serves multiple functions: it provides the unique identifier generation, acts as the challenge-response verification mechanism, and eliminates the need for separate timing hardware. The existing SRAM bit cells perform both storage and timing function simultaneously
Solution Approach 2:
The SRAM bit cells inherently provide the timing characteristics needed for the PUF without requiring external timing measurement hardware. The physical variations in bit cell read access times serve as the unique identifier, making the system self-sufficient for security purposes
3Reliability
If conventional PUF challenges are used, then the implementation is straightforward, but the PUF is susceptible to delayering and probing attacks
Solution Approach 1:
The patent replaces conventional challenge-response PUF mechanisms with a timing-based measurement approach. Instead of using complex logical challenges and responses, the system measures the time duration of bit cell operations, substituting mechanical/logical complexity with temporal measurement simplicity
Solution Approach 2:
The timing measurement acts as an intermediary that captures the physical characteristics of bit cells without requiring direct access to or manipulation of the underlying hardware structure. This temporal mediation prevents direct probing and delayering attacks while still providing unique identification
Data Source
AI summary
Methods and apparatus for creating a physically unclonable function for SRAM are disclosed. An example method includes after applying a voltage to a memory array: determining a first duration between the applying of the voltage and a first output of a first bit cell, the first output corresponding to a first value stored in the first bit cell, and determining a second duration between the applying of the voltage and a second output of a second bit cell, the second output corresponding to a second value stored in the second bit cell. The example method further includes determining a function based on a comparison of the first duration and the second duration, the function to establish an identification of a circuit that includes the memory array.