Security · 2026-03-08
Identity is a Physics Problem, Not a Math Problem
By J. W. Bouckaert
The cryptographic ceiling
Post-quantum cryptography (PQC) is a significant advance. NIST's FIPS 204 standardizes ML-DSA (formerly CRYSTALS-Dilithium), a lattice-based signature scheme, and FIPS 203 standardizes ML-KEM for key encapsulation. Both resist the quantum attacks known today. PasskeyBridge co-signs verifiable credentials with ML-DSA, and Enterprise tenants can turn on ML-DSA signing for cross-references.
But PQC solves a math problem. It replaces RSA and elliptic-curve schemes, whose underlying problems (factoring and discrete logarithms) Shor's algorithm solves on a large enough quantum computer, with schemes built on problems no known quantum algorithm solves efficiently. What it cannot solve is the physics problem: proving that a credential is bound to a specific physical device in a specific physical location at a specific moment in time.
This is the gap that NF-08, our Spatially-Bound Identity Attestation specification, addresses.
Limits of mathematics alone
Consider the threat model. An attacker with a quantum computer could break RSA and ECC. PQC defeats that attacker.
But what about an attacker who:
- Clones a private key from a compromised device?
- Replays a valid credential from a different geographic location?
- Simulates the cryptographic ceremony in a virtualized environment?
PQC cannot detect any of these attacks. The math is correct; the physics is wrong.
For a deeper look at how PasskeyBridge handles post-compromise scenarios, see Why SIM-Swap Detection Is Not Enough and our parametric revocation architecture.
The NF-08 Atomic Fingerprint
NF-08 introduces the concept of an Atomic Fingerprint: a composite hash derived from physically non-deterministic sensor readings captured within a strict temporal window (≤100ms).
The fingerprint is a SHA-256 digest over one digest per channel:
- EMI spectral: magnetometer readings, used as a proxy for the device's electromagnetic environment where the browser exposes the sensor
- Thermal variance: on-die thermal readings on a native client; in the browser, a best-effort signal built from memory pressure, core count and timer residuals
- Accelerometer: motion samples, at 60 Hz by default
- Network jitter: timer deltas, the connection estimate and Resource Timing deltas
- Device identifier: a digest over device and software identifiers; the device model is one of its inputs and is never sent on its own
The sensor readings change from one capture to the next, so two captures from the same device produce different channel digests. A channel digest that repeats exactly is a sign of replay.
The NF-08 flow
When a high-security authentication event occurs, the NF-08 flow proceeds as:
- Trigger: the relying party asks for a capture before a critical action, such as a high-value transaction
- Capture: the client reads its sensors within a window of at most 100 ms
- Hash: each channel's readings are hashed with SHA-256 on the device, and only the digests are sent
- Submit: the client posts the digests to the Spatial Binding Controller; a capture may carry the client's own ML-DSA signature, which is stored with it
- Check: the server refuses a capture that took longer than 100 ms or whose timestamp is more than 500 ms from server time, stores the digests, and either enrolls them as the user's baseline or compares them with that baseline
On a verification, a different device digest adds 0.8 to the anomaly score, a repeat of the baseline's EMI and thermal digests adds 0.5, and a repeat of its network-jitter digest adds 0.4. A score of 0.45 or more returns anomaly_detected with HTTP 403 and writes a failed audit entry. What happens next, such as a step-up, is the relying party's decision.
The dual-path architecture
NF-08 requires a dual-path implementation:
Backend: Spatial Binding controller
The Spatial Binding Controller enforces the capture window and the clock check, validates each capture, and scores each verification against the enrolled baseline. It runs as the shield-spatial-bind edge function on the Enterprise plan and stores digests in shield_atomic_fingerprints and bindings in shield_spatial_bindings.
Client: browser module and native access
PasskeyBridge's browser capture module reads what a browser exposes: network timing, the accelerometer and magnetometer through the Generic Sensor API where the browser supports it, and environmental signals in place of thermal sensors. Raw EMI and on-die thermal readings are not available to a browser and need a native client with privileged sensor access.
NF-08 is designed for high-security uses:
- Military device attestation: Proving a credential is bound to an authorized hardware unit
- Financial terminal binding: Ensuring trading terminals are physically present in verified locations
- Critical infrastructure: Binding operator credentials to specific control room hardware
See also: Reg S-ID Compliance Without Storing a Single Phone Number for regulatory alignment.
Scope of NF-08
NF-08 does not replace passkeys, PQC, or verifiable credentials. It sits alongside them as an additional attestation layer for scenarios where cryptographic proof is necessary but not sufficient.
For most consumer applications, WebAuthn passkeys (Pillar III) provide adequate hardware binding. Verifiable credentials (Pillar II) carry an ML-DSA proof beside their classical signature.
NF-08 is for the edge cases where you need to prove more than "the right key signed this". It proves "the right key signed this, on this device, in this location, at this moment."
Integration with PasskeyBridge
NF-08 is a separate check that a relying party calls through shield-spatial-bind with an API key carrying the spatial scope. A binding can name the passkey credential it belongs to. No playbook action starts a capture, and no verifiable credential or passkey ceremony requires one: the relying party decides when to ask for a capture and what to do with the result.
NF-08 is available on the Enterprise plan. Contact us to discuss your use case.
Summary
Post-quantum signatures keep a signature from being forged with a quantum computer. They do not show which device used the key.
NF-08 is PasskeyBridge's way of checking that: it compares what a device's sensors report now with what they reported at enrollment, and returns the score and the reasons to the relying party.
Read the NF-08 specification → | Build your first playbook →