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Trust

Hardware Root of Trust

Identity from the die, not from flash

Per-die identity is derived from manufacturing variation. There is no stored private key to read out, clone or reflash.

RTL in progress Pre-silicon
Status
RTL in progress
Identity source
Physical unclonable function
Scope
Per-die, unique
Key at rest
None
Stability
Error-corrected across operating range

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
Hardware Root of Trust · labelled architecture
Infrastructure equipment in the field conditions this mechanism is designed for
Field condition the mechanism is specified against
PROBLEM

A key written into a device can be taken out of it

Provisioning a private key into OTP or flash makes identity a physical object inside the package. With physical access over a long service life, extraction and cloning undermine every guarantee built on that key.

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.
Derive identity; do not store it · design intent
APPROACH

Derive identity; do not store it

A physical unclonable function reconstructs identity from die variation when needed. Invasive analysis disturbs the structure the measurement depends on, so the attack destroys the value it was trying to read.

Semiconductor die macro
Semiconductor die macro
PROPERTIES

What follows from the diagram

  1. Per-die derivation

    Compromising one part yields nothing about any other die

  2. No key at rest

    Nothing in flash or OTP for an attacker to extract

  3. Stable reconstruction

    Helper data and ECC hold a stable value across temperature

  4. Anchor for the stack

    Boot, verification and attestation all chain to this identity

Engage

Reviewing this mechanism?

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

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