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Trust

Device Attestation

Evidence a verifier can check

An attestation bundle is signed with per-die identity, binding boot measurement, firmware, model and result digest. Trust is decided by the verifier, never by the device.

Architecture defined Pre-silicon
Status
Architecture defined
Bundle binds
Identity, firmware, model, result digest
Freshness
Nonce online, counter offline
Signing
Classical and post-quantum
Offline
Queued and exported in order

Design targets · not measured silicon results

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Trust domain Trusted compute
Nelix trusted compute domain Floorplan with four nested planes: board domain, package, die, and a central trust island for device identity, measurement and signing. Compute, memory, sensor I/O, metrology, crypto and telemetry route into a ring bus. Only signed data leaves through an attestation export port. Board domain Package Die Die extent Package extent Compute Bounded array Memory Measured store I/O phy Sensor ingress Metrology Sense & sample Crypto Sign & seal Telemetry Signed export Ring bus Trust island Root of trust Key slots Identity · measure · sign Port signed Attestation export Nothing else crosses
  • Trust boundary
  • Supporting logic
  • Signed data in flight
Device Attestation · labelled architecture
Infrastructure equipment in the field conditions this mechanism is designed for
Field condition the mechanism is specified against
PROBLEM

Self-reported health is not evidence

Compromised firmware reports whatever suits it. Signing only helps if the key is out of reach, and a captured attestation without freshness proves yesterday, not now.

While running Runtime verification
Continuous runtime verification A conceptual die floorplan for continuous measurement. An always-on measurement engine occupies the left of the die, with a four-phase cycle beneath it: sample, hash, extend, compare. To its right a recessive band shows workload activity in three lanes of uneven task footprints. A sample bus runs under the band and a comb of taps drops from it into a digest chain of linked cells, one per epoch, which the light extends from left to right. One epoch is flagged and re-measured. Beneath the chain the measured history stacks downward in rows that fade as they age, and the chain has no entry from its left end, so the record can only be extended and never rewound. Fresh evidence leaves through a port on the right edge. Operating die · power on Measure engine Always on Sampler Hash macro Every epoch not only at boot Sample Hash Extend Compare Workload activity L0 L1 L2 Sample bus Rolling digest E0 E1 E2 E3 E4 E5 E6 No rewind Re-measure Measured history E6 E5 E4 E3 Fresh quote Measurement continues for as long as the device runs
  • Measured epoch
  • Flagged for re-measure
  • Light = the digest being extended
Boot-time proof goes stale, so measurement continues while the device works and the evidence an operator asks for is always current.
Bind evidence to die, firmware and workload · design intent
APPROACH

Bind evidence to die, firmware and workload

TrustCore signs a bundle the verifier checks against approved configurations. Online freshness uses a nonce; offline sites queue against a monotonic counter so gaps stay visible.

ORDER OF OPERATIONS

Sequence

Order is the mechanism, and nothing here is optional.

Sequence Device Attestation
The enforced order of operations, 6 steps from first to last Sequence diagram with a trunk on the left edge. Steps in order: Challenge; Collect; Sign; Export; Verify; Admit. Gate ticks sit between steps; the last step is the only exit. Enforced order 01 Challenge Verifier nonce, or local counter when offline 02 Collect Boot, firmware, model and result digest gathered 03 Sign TrustCore signs with per-die identity 04 Export Bundle leaves with the result, or queues locally 05 Verify Signature, freshness and measurements checked 06 Admit Only a passing bundle enters the workflow No step may be skipped The enforced order of operations, 6 steps from first to last Sequence diagram with a trunk on the left edge. Steps in order: Challenge; Collect; Sign; Export; Verify; Admit. Gate ticks sit between steps; the last step is the only exit. 01 Challenge Verifier nonce, or local counter when offline 02 Collect Boot, firmware, model and result digest gathered 03 Sign TrustCore signs with per-die identity 04 Export Bundle leaves with the result, or queues locally 05 Verify Signature, freshness and measurements checked 06 Admit Only a passing bundle enters the workflow
  • Ordered step
  • Only exit
Each step taps the trunk once; the gates between them are why the order holds.
Semiconductor die macro
Semiconductor die macro
PROPERTIES

What follows from the diagram

  1. Per-die signature

    One part cannot forge evidence for another

  2. Measurements in payload

    Boot, firmware and model versions are stated explicitly

  3. Freshness

    Nonce online; ordered counter offline

  4. Verifier-side policy

    Approved configs live with the operator, not the device

Engage

Reviewing this mechanism?

The specification can still change. That stops being true after tape-out.

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