What is proof of location

Definition

What is proof of location?

Proof of location is a cryptographically signed statement that a specific device was inside or outside a defined region at a specific time, verifiable afterwards by someone who trusts neither the device’s owner nor the vendor that produced it.

An estimate and a proof are different things

Most location systems return an estimate. An IP lookup, a GPS fix and a browser Geolocation response each report where something appears to be. The software that reports them can change them, and the receiver cannot tell.

A proof adds a signature that the reporting software cannot produce on its own. If anyone alters the statement or replays it on another device, the signature fails to verify.

The test: can someone who trusts nobody involved verify it later, without asking the vendor?

To get a YES from outside the region, an attacker has to fool the statistical proof the phone builds before it computes location. That proof draws on hundreds of inputs, from inertial sensors to radio signals to on-device data that other location methods usually ignore. No location-spoofing method seen to date fakes all of them so that they agree with each other over space and time.

What a proof contains

A proof of location carries a verdict rather than a coordinate. Most rules ask whether a device is inside a region, not exactly where it is, and a verdict answers that while disclosing less. In Octet a proof answers a predicate such as isWithin or isOutside against a named region and returns YES, NO or INDETERMINATE.

YES and NO each carry a signed proof.
INDETERMINATE carries a reason and no proof. “The device was elsewhere” and “the device could not tell” are different answers, and a relying party needs to know which one it got.
The coordinates stay on the device and are not part of the proof.

Who checks it, and how

A proof is worth as much as the way it is verified. If verifying it means calling the vendor’s API and accepting the answer, the relying party is trusting the vendor, and the proof records only the vendor’s opinion. Octet proofs verify offline with octet-verify, an open-source command-line tool, so a regulator, auditor or counterparty can check one without contacting Octet.

The signing key lives in the device’s secure hardware, and the platform vouches that the hardware and the app are genuine. Device-attested location describes how this works. Cryptographic proof of location covers the other approaches and where each fails.

What this does not establish

A verdict answers for a device, not a person. It says an enrolled device was inside or outside a region at a time. It does not say who was holding it. Use it alongside identity verification, never instead of it. It does raise the cost of cheating: instead of a VPN subscription, a cheater needs real devices and a person in the permitted place for every transaction.