A signed answer can only travel so fast. We time it, and the speed of light puts a hard ceiling on how far away the GPU can be.
An anchor we trust sits in Tashkent. The GPU server runs a small agent. Every check takes a fraction of a second.
The anchor sends a fresh random number that nobody could have guessed in advance.
The agent on the GPU server signs it with a key tied to that GPU and returns the signature.
The round-trip time caps the distance. Light in fiber covers about 200 km per millisecond, so the reply could not have come from farther.
The anchor is a Mac in Tashkent. Each row is a real run against a real machine.
| Prover | Round trip | Distance bound |
|---|
These are upper bounds. Belgium is really about 4,800 km away; routing, tunnels and processing only add time, so the bound is loose but never wrong.
Timing proves a chip is no farther than X. It cannot prove it is exactly here.
One checker proves distance, not a border. Shymkent, Kazakhstan is about 120 km from Tashkent. Several anchors in different cities narrow it to inside the country.
Until the key is bound to hardware attestation, a copied key could answer from another machine. That is the next milestone.
Tunnels and relays can only make a host look farther, never closer. The relay test above was caught exactly that way.
Evidence for licences, compliance and customers that their chips stay in the country.
Banks and ministries that must show where their workloads physically ran.
Sell country-pinned pools with per-job proof instead of a promise.