DUTY CYCLE BASED PHYSICAL UNCLONEABLE FUNCTION 3.1 Introduction
3.14 Adaptable Duty Cycle Based PUF Conclusions
A variable duty cycle PUF primitive is proposed for security applications. The proposed PUF primitive is demonstrated to be stable over the worst case and best case manufacturing process, supply voltage, and temperate variations. The proposed PUF primitive uses current starved inverters, thus reducing the power requirements. The feedback utilized to maintain a robust duty cycle under PVT variations uses a simple, stable circuit that provides a fast response with an
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effective compensation over the operating ranges. The proposed PUF primitive is configured and controlled with digital inputs for security adaptation and therefore well suited for programmable applications, portable applications requiring low power and small area.
68 CHAPTER 4: FINAL CONCLUSIONS
A novel implementation and application of pulse width modulator has been studied and demonstrated with analysis and simulations at system and circuit level. A novel duty-cycle based PUF and variations of the architecture has been studied and demonstrated with system analysis, circuit implementations and a wide range of simulation results.
The proposed designs have been qualitatively and quantitatively compared with state-of- the-art work and has been demonstrated to be well defined, superior and, comparable in attributes and merits. The work has been accepted for publications in leading technical journals and conferences for a successful scholarly demonstration.
69 CHAPTER 5: FUTURE WORK
The PWM circuit described in Chapter 2 can be used with a variety of circuits that require variable duty cycle and or fixed / variable frequency. Two of the applications of the circuit, the voltage regulator, converter and a stable physical unclonable function are described and demonstrated in this work through analysis and simulation. In addition other applications such as Class D power amplifier control can be explored and demonstrated with the use of the PWM.
One of the major weakness of the ring oscillator PUF (ROPUF) is the limited number of challenge response pairs (CRP) compared to an arbiter PUF. The controlled and adaptable PUF proposed in Chapter 3, Section 3.11 can be further enhanced to provide a wide distribution of duty cycle at each node of the ring oscillator PUF. This will ensure a high entropy of duty cycle distribution and potentially increase the number and quality of randomness of the challenge response pair, thus making the PUF a strong PUF. A complete study of this feature is recommended as a future plan of work. This will require support for an appropriate parallel circuit simulation environment.
The PUF control circuit can be configured to produce a non-linear output duty cycle behavior. This can help in developing a PUF that is resistant to machine learning attacks. Recent attempts to combine security and voltage regulation methods on IC have been described in Introduction Chapter 1, Section 1.3. The present duty cycle controlled PWM based PUF can be used in phases of duty cycle shuffle during its operation with a voltage regulator converter circuit to potentially provide security against power profile, side channel and leakage attacks on the
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integrated circuit through the power network. A future fabrication of the circuit and measurement data from the fabricated circuits will confirm the full functionality in a real application. This will help to further confirm and demonstrate the novel ideas proposed in this work.
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