Physically Unclonable Function

Silicon Signature

Random variations in transistor gate dimensions and line widths determine the behavior of the circuit under test. A physically unclonable function uses these variations to generate a unique response when a specific challenge is applied to the array. This challenge-response pair behaves like a cryptographic key but is born from the physical structure of the chip.

This structure makes the key immune to physical memory extraction techniques.

Key Extraction

Internal circuitry converts the analog startup states of SRAM cells into a stable digital key. The physically unclonable function uses helper data and error correction codes to ensure that the generated key remains identical across varying temperatures and supply voltages. This stabilization is critical for generating reliable cryptographic keys from noisy physical processes.

The key is reconstructed only when needed and erased immediately after use.

Circuit Behavior

Attacking the physical structure of the chip alters the underlying analog characteristics and destroys the key itself. A physically unclonable function provides an inherent defense against probe attacks because any attempt to drill or scrape the silicon changes the capacitance of the circuit. This change alters the startup state of the transistors and invalidates the generated signature.

This defense secures the device against sophisticated laboratory extraction attempts.