Silicon Reverb (2024)

 

A Year Later: Reflections on Low-Cost Hardware Security and Beyond

It’s hard to believe it has already been a year since I presented and published my paper “Silicon Reverb: Non-Invasive Low-Cost Solution for Detecting Hardware Trojans” at IEEE NAECON 2024. The paper presented a scalable, accessible methodology for non-invasive trojan detection in FPGAs using low-cost tools like the LibreVNA and Digilent Digital Discovery. What started as a class project in replicating the work of Silicon Echoes, a groundbreaking approach to frequency-selective impedance analysis for Trojan detection, has since evolved into a broader exploration of how impedance-based methods can be applied beyond just hardware security.

How It Started: The Influence of Silicon Echoes

When I first read the Silicon Echoes paper by Mosavirik et al., I was struck by how elegantly it combined RF analysis with hardware security. Their use of a Keysight PNA and NEWAE CW305 FPGA Target Board was, frankly, cost-prohibitive for most labs or individual researchers, but it set a high watermark for non-invasive analysis. Silicon Reverb actually began as a class project, and my goal was to democratize access to similar techniques, achieving comparable results with just 0.5% of the budget by using accessible equipment. This philosophy remains central to my ongoing research.

Cooling Fans and Serendipitous Discovery

While writing my thesis and diving deeper into related work, I recently stumbled upon Garren Dutto’s 2025 M.S. thesis from the University of Oregon. To my amusement (and appreciation), I found that he had also employed the LibreVNA in his work. One key difference? I addressed many of the LibreVNA’s thermal stability issues—which Dutto documented in some detail—by adding cooling fans directly into the VNA’s enclosure. Thermal drift is no joke at GHz frequencies, and even a modest airflow solution made a meaningful difference in repeatability and noise floor behavior.

The cooling fans I added to the LibreVNA

The temperature reduction that was observed with my Flir One camera

Beyond Security: Expanding Applications

Over the past year, my focus has shifted toward using impedance spectroscopy and related measurements not only for security but also for general hardware characterization and anomaly detection. Impedance responses tell a story—a kind of electrical fingerprint that reveals subtle changes due to power draw, temperature shifts, or even physical damage. 

What Comes Next

As I wrap up my thesis, I’m also prototyping new hardware/software tools to better automate these measurements and streamline data analysis. The LibreVNA remains my go-to platform.

More broadly, I’m encouraged to see continued contributions from the WPI team behind Silicon Echoes, whose newer work continues to push the boundaries of side-channel analysis and non-invasive verification. Their contributions validate and extend the foundational ideas I built upon.

Acknowledgments

This journey wouldn’t have been possible without the support of my employer, Two Six Technologies, and the continuing encouragement from the community around Hong’s Electronics. If you’ve made it this far, thank you for reading. If you’re working on anything related or curious about the techniques I’ve explored, don’t hesitate to reach out.

–Jeremy