Proof of Location

Proof of Location records witness-attested evidence for a location claim: operators time a network round trip to the device and sign what they measured, and a commitment to a coarse cell of the claim is recorded on Ethereum Sepolia testnet.

What is proof of location?

Location claims are easy to fake. GPS coordinates are self-reported by the device, and GPS itself can be spoofed with commodity hardware. Any workflow that pays, credits, or authorizes based on "I was there" needs evidence from someone other than the device.

Proof of location systems make a claim checkable: parties other than the device measure something about it, such as network timing, sign what they measured, and package that evidence so a third party can check it later. How strong the evidence is depends on what is measured and who the witnesses are.

Privacy comes from keeping the claim coarse. What goes on-chain is a commitment and a geohash cell of about 5 km with its time, not a trajectory, and the commitment does not name the user. The cell and time are public and permanent, so get informed consent before submitting.

Diagram: a phone submits a location claim. Offline Protocol's backend commits a coarse geohash cell to a contract on Ethereum Sepolia testnet, a witness operator times a network round trip to the phone and signs an EIP-191 attestation, and the app's backend verifies that attestation.

A claim, witnessed and checked: the backend records a commitment to a coarse cell and a time on Ethereum Sepolia testnet, a witness operator times a round trip to the phone and signs what it measured, and your backend verifies that attestation against its own policy.

What a result means, and what it does not

A Proof of Location result is narrower than a coordinate. A witness operator measures the round-trip time between itself and the device and compares the distance that timing implies with the distance from its own location to the claimed one. The implemented rule accepts a claim when the two distances differ by less than 20 km, or when the round trip is between 0.8 and 1.5 times the theoretical minimum for the claimed distance.

That makes some claims implausible, such as answering from another continent, but it does not prevent spoofing: a client can add delay, and the witness trusts the claim fields the client sends. A signature authenticates the witness's statement, not the truth of the location. It is not a zero-knowledge proof and not proof that a person was physically present. The claim is submitted with the user's OfflineID session.

Disclosure stays narrow: the chain records a commitment and a coarse cell with its time, and no service stores the submitted coordinates. For workflows like chain-of-custody in logistics, treat a result as one signal alongside your own checks.

Verifying a result

Offline Protocol's backend commits a geohash of the claim to an EigenLayer AVS contract on Ethereum Sepolia testnet. Each witness operator responds on-chain and returns its own EIP-191 attestation over a WebSocket. No step aggregates them into a final proof.

Your backend verifies each attestation against an approved signer, the expected chain and contract deployment, the task, and a freshness window. An API 200 or an indexer row is not a location proof.

Use it to evaluate location-evidence workflows, such as rewards for being at a place, region-scoped access, or presence at events, and not as the only control for attendance, payments, compliance, or geographic access. The architecture and security boundaries pages in the docs carry the details.