Silicon PUF Unique Data Generation via TDC Delay Measurement
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Solution Overview
Problem
Existing Physically Unclonable Functions (PUFs) for silicon integrated circuits face issues such as significant latency, high energy consumption, large size, vulnerability to reverse engineering and side-channel attacks, and determinism in response generation due to measurement of frequency variations rather than direct delay measurements.
Innovation Solution
A method using a digital time converter (TDC) to measure the difference between the time of arrival of a first and a second event in a signal generated by a delay circuit, with the generation of double or multiple pulses to transform the signal and reduce determinism, allowing for precise and fast measurement of propagation delays to generate unique data.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If frequency measurement methods are used to generate unique data, then the measurement can be performed, but the latency becomes significant and energy consumption increases
Solution Approach 1:
The patent replaces frequency measurement methods with direct time delay measurement using a Time-to-Digital Converter (TDC). This substitution changes the measurement approach from counting oscillations over time to directly measuring the time interval between two events, thereby reducing the measurement time and latency while maintaining the ability to generate unique circuit-characterizing data.
Solution Approach 2:
The patent changes the measured parameter from frequency (number of events per period) to direct time delay (duration between two events). By measuring the time delay directly with a TDC instead of counting oscillations, the measurement process is accelerated significantly, reducing latency from microseconds to nanoseconds while still capturing the unique circuit characteristics.
2Measurement precision
If frequency measurement methods are used to generate unique data, then the measurement can be performed, but energy consumption becomes excessive
Solution Approach 1:
The patent replaces energy-intensive frequency measurement circuits with a TDC-based time delay measurement system. The TDC consumes significantly less energy because it performs a direct time interval measurement without requiring prolonged oscillation counting, thereby reducing the energy consumption associated with generating unique circuit data while maintaining measurement precision.
3Ease of manufacture
If static structures are used as PUF sources, then the structure is visible and can be easily copied
Solution Approach 1:
The patent replaces static, visually-inspectable PUF structures with dynamic time delay measurements performed during circuit operation. Instead of relying on fixed physical structures that can be observed and copied, the system measures the propagation time of signals through the circuit's logic elements, creating a unique signature that is functional rather than structural, thereby enhancing security against reverse engineering.
4Reliability
If memory initial state is used as entropy source, then the secret is hidden when circuit is off, but it becomes readable when powered on
Solution Approach 1:
The patent replaces memory-based entropy sources with direct time delay measurements of signal propagation through logic circuits. This substitution eliminates the vulnerability where memory contents become readable when powered on, as the unique signature is derived from the intrinsic propagation delays of the circuit's logic elements during operation, not from stored memory states that can be extracted via side-channel attacks.
5Measurement precision
If multiple oscillators are used to extract entropy, then measurement stability improves, but the circuit size becomes large
Solution Approach 1:
The patent replaces multiple oscillator circuits with a TDC-based time delay measurement system. The TDC directly measures the propagation time through the circuit's logic elements, achieving stable and precise unique data generation without requiring multiple oscillators. This substitution significantly reduces the circuit area while maintaining or improving measurement stability, as the time delay inherently captures the circuit's unique characteristics.
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
This approach significantly reduces latency and energy consumption, enhances security by minimizing side-channel attacks, and increases the robustness of the unique data generated, making it more resistant to attacks and efficient in terms of size and energy usage.
Implementation Method 1
measuring, using a time-to-digital converter (hereinafter "TDC"), the difference between: i) the time of arrival of a first event of a signal at an input of the TDC and, ii) the time of arrival of a second event of a signal at an input of the TDC, the second event being generated by the delay circuit
Data Source
Figure 1
Figure 2a~2b
Figure 3a~3b
AI summary
The invention relates to a method for generating a unique data (R) specific to a silicon integrated circuit, said data being generated by the application of a physically non-clonable PUF function of said circuit, which circuit includes a delay circuit (CR, CRi), the implementation of the PUF function includes a step consisting of measuring, by means of a TDC converter, the difference between: - the time of arrival of a first event of a signal at an input (Start) of the TDC converter and, - the time of arrival of a second event of a signal at an input (Stop) of the TDC converter, which second event is generated by the delay circuit (CR).