THREAT ASSESSMENT: Single-Trace Side-Channel Break of NIST-Standardized FALCON PQC on Embedded Systems
![full screen view of monochrome green phosphor CRT terminal display, command line interface filling entire frame, heavy scanlines across black background, authentic 1970s computer terminal readout, VT100 style, green text on black, phosphor glow, screen curvature at edges, "FALCON PRIVATE KEY EXFILTRATED VIA POWER TRACE #001", monospace green text glowing faintly on deep black terminal screen, text slightly blurred as if captured from a live feed, dim ambient glow from inactive keys, atmosphere of silent, irreversible compromise [Nano Banana]](https://081x4rbriqin1aej.public.blob.vercel-storage.com/viral-images/4ad489f2-af51-4015-8e7f-ef1591cae1c4_viral_0_square.png "full screen view of monochrome green phosphor CRT terminal display, command line interface filling entire frame, heavy scanlines across black background, authentic 1970s computer terminal readout, VT100 style, green text on black, phosphor glow, screen curvature at edges, \"FALCON PRIVATE KEY EXFILTRATED VIA POWER TRACE #001\", monospace green text glowing faintly on deep black terminal screen, text slightly blurred as if captured from a live feed, dim ambient glow from inactive keys, atmosphere of silent, irreversible compromise [Nano Banana]")
A curious pattern emerges in the power traces of FALCON’s key generation: a single 63-bit shift, meant to be invisible, whispers the secret away. What was designed to withstand quantum storms now yields to the quietest of whispers from the machine itself.
Bottom Line Up Front: FALCON, a NIST-standardized post-quantum digital signature scheme, is vulnerable to full secret key recovery via a single power trace side-channel attack (SHIFT SNARE) during key generation, posing an imminent risk to embedded and IoT implementations.
Threat Identification: The SHIFT SNARE attack exploits information leakage from a 63-bit right-shift operation in the discrete Gaussian sampling component of FALCON’s key generation. This leakage reveals the sign (1 vs. 0) of intermediate coefficients, enabling full reconstruction of the secret key from one power trace. The attack was validated on ARM Cortex-M4 using both reference and optimized implementations from FALCON’s NIST Round 3 package.
Probability Assessment: The attack is already demonstrated and reproducible. With a per-coefficient success rate of 99.9999999478% and full-key recovery rate of 99.99994654% for FALCON-512 based on over 500,000 statistical tests, the likelihood of successful exploitation in vulnerable environments is effectively certain (Timeline: Immediate, 0–3 months) [Citation: arXiv, 2026].
Impact Analysis: High to severe. FALCON is designed for use in constrained environments (e.g., IoT, embedded systems) where side-channel protections are harder to implement. Compromise of the signature key enables forgery, impersonation, and breakdown of trust in PQC-secured channels. The fact that all included implementations in FALCON’s NIST submission are vulnerable suggests widespread exposure. This undermines confidence in the deployment timeline for quantum-safe standards.
Recommended Actions: 1) Suspend deployment of FALCON in side-channel-exposed environments (e.g., embedded, smart cards) until patches are vetted. 2) Implement constant-time, single-trace resistant software countermeasures in Gaussian sampling routines. 3) Conduct urgent audits of all FALCON implementations for similar shift-based leakage patterns. 4) Prioritize deployment of alternative signature schemes (e.g., Dilithium) with stronger side-channel resistance in the interim.
Confidence Matrix: Threat Existence – High (demonstrated proof-of-concept). Probability – High (empirically validated success rates). Impact – High (core cryptographic primitive compromised). Mitigation Maturity – Low (no public patches as of current date).
—Ada H. Pemberley
Dispatch from The Prepared E0
Published January 2, 2026