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Entropy Extraction in Metastability-based TRNG

Presented by

Cheng Chung Wang & Hsi Shou Wu

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Outline

• Background• Motivation• Implementation and analysis• Conclusion• Discussion

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Background

• TRNG : True Random Number Generators• Entropy : Natural Sources– Cosmic rays– Stray electromagnetics waves– Thermal noise

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Background cont’d

• Process variation and operating condition will impact the output of TRNG circuits

TRNG1

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Temperature

Fabrication defect

Operating voltage

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Background cont’d

• Bias Removal Techniques– Post-processing techniques– Calibration techniques

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Background cont’d

• Post-processing techniques– XOR– Von Neumann corrector (entropy extractor)

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Background cont’d

• Calibration– Phase of clock signal– Charge injection

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Motivation

• Several proposed biased removal circuit.• Which one is the best solution?• “Action speaks louder than words”

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Implementation and analysis

• TRNG without correction

Advanced technology

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Implementation and analysis

• With XOR

Depend on the max entropy one

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Implementation and analysis

Drawback:1. not generate at const rate!2. Effective bit rate decrease with technology scaling

• With Von Neumann correctorEnhance entropy a lot

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Implementation and analysis

• TRNG with calibration

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Implementation and analysis

• TRNG with calibrationIncrease entropy but remain const output rate

Less energy overhead

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Implementation and analysis

• TRNG with calibrationTradeoff between number of bits entropy and energy consumption

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Conclusion

• 1. Modern security systems need on-chip true random number generators.

• 2. Conventional post-processing techniques are not efficient for simple TRNG – Physical calibration techniques are required .– provide a greater flexibility for trading off entropy

for energy

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Discussion

1. Is the referenced model (dual inverter) representative?

2. Will the results change if we also run Monte Carlo simulation in other parameters (temperature or voltage drop)?

3. Would the area overhead be a huge issue?4. As technology scaled down, dose the experiment

result still make sense?5. Is bit generation rate a more important issue?