A Novel SRAM-based Cross-Coupled BRAM PUF Featuring Entropy-Driven Addressing for AMD FPGAs

SRAM-based Physically Unclonable Functions (PUFs) are critical for securing FPGA-based embedded systems. However, traditional implementations face significant limitations: they typically require power cycling to extract entropy or rely on external complex circuitry to drive address sequences, potentially creating a larger attack surface for adversaries. This paper proposes a novel, fully standalone PUF architecture on AMD FPGAs that uses the timing violations of read and write operations. Unlike prior collision-based designs that depend on externally supplied random addresses, our proposed architecture introduces a mutual feedback loop where the metastable response of one Block RAM dynamically determines the address of its cross-coupled counterpart. This mechanism creates a self-sustaining entropy source that functions without depending on an external driver or power cycling. The design was implemented and validated on eight AMD Artix-7 FPGAs using a custom MicroBlaze-based data acquisition system. Experimental results demonstrate that the CC-RIWC PUF achieves an average uniqueness of 41.45% and reliability up to 98.37% across a wide temperature range ( \(-18^{\circ}C\) to \(50^{\circ}C\) ). While the self-driving cross-coupled architecture introduces a trade-off in resource usage (44 slices) and throughput (900 Mbps) compared to externally-driven primitives, it provides a superior architectural advantage by delivering a complete, standalone entropy primitive suitable for resource-constrained, always-on embedded systems like Internet-of-Things.