Technical detail

Brass and Aarne give the distance bound as D = T × 200, where D is the maximum distance in km and T the one-way delay in ms, taking about 200,000 km/s as the speed of light in optical fibre ¹. In their case study, a 4.665 ms one-way delay bounds the chip to within 933 km of the landmark ¹. They note that a limit based on the vacuum speed of light, about 300,000 km/s, covers worst cases such as out-of-band radio or satellite links and cannot be beaten physically ¹. The cost is more false negatives: honest chips near a landmark may not reply fast enough, which the authors' moderate experimentation suggested could happen "perhaps even in more than 50% of cases" ¹. Calibrating landmark delay factors might reduce this rate but needs further work ¹. Recent geolocation algorithms reach a median error under 10 km given excellent landmark distribution and coverage; delay-based methods in general give about 10 km to 1,000 km, depending on the algorithm ¹.

The Sovereignty Certificates draft (Lucid sovereignty (location) certificates) casts the protocol as a RATS (RFC 9334) attestation flow with Entity Attestation Token (RFC 9711) claims ¹⁰. The verifier issues a nonce and a signed directory of anchors. The attester probes anchors from inside a TEE, and each anchor returns a signed receipt with a high-precision timestamp and a nonce. The verifier then runs a deterministic multilateration to compute a feasible region ¹⁰. Per-cycle ephemeral keys are bound into the hardware root of trust's attestation quote to prevent replay ¹⁰.

Tee and Happel propose identifying a GPU by a hardware fingerprint instead of an extractable on-chip key. Their proof of concept races atomic operations across streaming multiprocessors ⁹. Over 480 runs on 24 NVIDIA H200 GPUs rented from a cloud provider, re-identification accuracy was 98.8% from a single run and 100% from paired runs, with each run taking about 2.9 s ⁹. The authors state that the fingerprint still has to be validated on more GPUs, shown to be stable over time and conditions, and shown to resist an adversary who runs the function faster or simulates the GPU ⁹.