Closed-Loop Spread Spectrum Clocking for Side-Channel Mitigation
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Solution Overview
Problem
Integrated circuits using spread spectrum oscillators with unpredictable average frequencies reduce component efficiency and are susceptible to side channel attacks due to unreliable electromagnetic emissions.
Innovation Solution
A closed loop oscillator circuit that operates in a spread spectrum mode by temporarily increasing and decreasing the frequency of the output clock signal within a predetermined multiple of the reference clock cycle, maintaining an average frequency locked to the reference clock for predictable performance and spreading electromagnetic interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If spread spectrum oscillators with unpredictable average frequency are used, then protection against side channel attacks is improved, but component efficiency and performance predictability deteriorate
Solution Approach 1:
The patent changes the frequency parameter of the oscillator dynamically by introducing spread spectrum modulation. The oscillator frequency is varied according to a pseudorandom sequence, transforming the single-frequency operation into multi-frequency operation. This parameter change spreads the electromagnetic emissions across a wider frequency range, making statistical analysis for side channel attacks much more difficult while maintaining predictable average frequency through closed-loop control.
Solution Approach 2:
The patent introduces dynamic behavior to the oscillator system by implementing frequency modulation according to a pseudorandom sequence. Instead of operating at a fixed frequency, the oscillator dynamically adjusts its frequency over time. This dynamic operation creates unpredictable electromagnetic emissions that vary in frequency, rendering traditional side channel attack methods ineffective while the closed-loop controller maintains predictable average frequency performance.
2Reliability
If spread spectrum oscillators with unpredictable average frequency are used, then protection against side channel attacks is improved, but performance predictability and consistency deteriorate
Solution Approach 1:
The patent implements a closed-loop feedback control system where the oscillator output is monitored and fed back to a controller. The controller adjusts the oscillator frequency in real-time according to a pseudorandom sequence while maintaining the average frequency at the target value. This feedback mechanism ensures that despite the dynamic frequency variations for spread spectrum operation, the average frequency remains predictable and consistent, preserving performance stability.
3Object-generated harmful factors
If traditional EMI reduction techniques such as shielding and filtering are used, then electromagnetic interference is reduced, but device complexity and cost increase
Solution Approach 1:
The patent converts the harmful electromagnetic emissions into a beneficial spread spectrum signal. Instead of trying to suppress or filter the emissions after they occur, the system proactively modulates the oscillator frequency to spread the emissions across a wide frequency range. This transformation turns the potentially harmful concentrated EMI into a dispersed, unpredictable signal pattern that is inherently more difficult to exploit for side channel attacks, eliminating the need for additional shielding and filtering components.
Data Source
AI summary
An integrated circuit includes a closed loop oscillator circuit portion. The closed loop oscillator circuit portion has an input for a reference clock signal and an output providing an output clock signal to one or more further components of the integrated circuit. The output clock signal has an average output frequency derived from the reference clock signal. The closed loop oscillator circuit portion is operable in a spread spectrum mode in which the closed loop oscillator circuit portion varies a frequency of said output clock signal, by temporarily increasing the frequency by a predetermined amount and temporarily decreasing the frequency by said predetermined amount, at different times, within a predetermined multiple of a clock cycle of the reference clock signal.