Energy-Aware Physical Unclonable Functions: From Physical Entropy Sources to MRAM-Based Low-Power Hardware Roots of Trust

Physical unclonable functions (PUFs) convert device-specific physical variations into responses for chip identity, key reconstruction, secure boot, and hardware roots of trust. This review examines the complete PUF chain from entropy generation and response digitization to stabilization, post-processing, deployment, security evaluation, and low-power implementation. Mature CMOS delay, SRAM, and DRAM PUFs are treated as engineering baselines, while representative emerging-memory PUFs provide comparison points for a MRAM-centered analysis. The main focus is placed on MRAM PUFs, including static MTJ variation, stochastic STT/SOT switching, response digitization and stabilization, reconfigurability, magnetic-specific attack surfaces, and system integration. The main contents include MRAM-PUF energy costs across device operation, raw-response generation, response stabilization, key reconstruction, and complete authentication. This cross-layer perspective distinguishes cell-level read/write energy from repeated sampling, reliable-bit-selection, ECC/KDF, controller, retry, and reconfiguration overheads. MRAM offers distinctive features including non-volatility, high endurance, and stochastic switching behavior. Their system-level energy benefits are treated as application-dependent and should be evaluated at the complete transaction level.