The idea is to protect the users' privacy while proving that person didn't appear in a dangerous area.

They who can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety. - Benjamin Franklin

The privacy is important. Let's care about privacy and allow authority instances (like Governance) to ensure that a person wasn't appeared in the COVID-19 affected area by generation proof that proves the User is outside the specified area. So Governance can control the spreading of a virus without tracking the exact location of all Users.

**This article and attached repo contain a proof of concept project made for the TON contest: **

#18 Groth16 zkSNARK Proof Verification Use Cases

The idea is to prove that you weren't in some specific area on the map without revealing your actual location.

To do so, we made a prototype by creating a zkSNARK widget that accepts Users' coordinates (as personal input) and generates proof that this is outside of a specified area defined by min and max coordinates (as auxiliary input).

1. Governance create a solidity contract with snark that can validate coordinates and get the answer, is the User placed in the specified area
2. User generates proof on his device and send it to the contract

1. User can confirm that he is in a safe area
2. User location data doesn't send outside of his device, so we preserve privacy

1. Let's assume that each user have unique secure device which generates proof with current coordinates as an input (which is never leave this device). In the demo we made a server that emulates this device.

2. Personal ID and Time assumption: In real world we have to provide secure device, that encrypt location on the user's side and they have to be bonded with location. So let's assume that a personal tracker can log it.

A zkSNARK checks that at least one of these constraints is true, using a comparison components from a blueprint library:

userLatitude <= minLatitude
maxLatitude <= userLatitude
userLongtitude <= minLongtitude
maxLongtitude <= userLongtitude

By running the script, you can Do trusted setup: Generate proving.key & verification.key Generate and save proof and primary_input to file by given coordinates and min/max coordinates Verify example (Check the status of the proof)

Validates proof on-chain using VERGRTH16 TVM instruction.

This web application interactively generates and validates proofs for a given user location and restricted area coordinates.

• Proofs are generating by a node backend with compiled blueprint CLI tool and pre-generated proving key;
• Proofs are validating on chain using verification.sol smart contract from a repo, deployed at: 0:e13752c9dc987ca1e33a012511409b273ea06af68e799c24f3cee861fc9815aa

address at Nil's test network;

• A verification key is stored in the smart contract and can be changed using the setVerificationKey method

1. Clone:

git clone  https://github.com/idealatom/zkp-covid-tracker --recursive

2. Go to build directory:

cd zkp-covid-tracker/zkp && mkdir build && cd build

3. Build

cmake .. && make cli

4. Generate proving and verification keys:

> bin/cli setup
Blueprint size: 284
Generating constraint system...
Number of R1CS constraints: 287
Generating key pair...
Saving proving key to a file "proving.key"
Saving verification key to a file "verification.key"

5. Generate the proof for given coordinates:

> bin/cli prove --posLat 13.686019 --minLat 13.673677 --maxLat 13.697777 --posLng 100.564981 --minLng 100.523192 --maxLng 100.551189
Loading proving key from a file "proving.key"
Generating constraint system...
Generating witness...
Blueprint is satisfied: 1
Generating proof...
Saving proof to file "proof"
Saving primary input to file "primary.input"

6. Verify proof file using saved primary input and verification key:

> bin/cli verify
Loading proof from a file "proof"
Loading primary input from a file "verification.key"
Loading verification key from a file "primary.input"
Verification status: 1

cd ./backend

npm install

npm run dev

> cd /frontend/
> yarn install
> yarn start

Then open localhost:8000 in your browser.

Build tests:

> cd /zkp/test/
> cmake .. -DBUILD_TESTS=1
> make circuit_test

Run tests

> test/circuit_test