qct / zk-example

An example to show how zk-SNARK works

zk rollup example

Problem

Let's say we want to solve a math problem: y = x^4 + x^3 + x^2 + x, I can prove you I know the answer without telling you the answer.

This example use gnark to help understand how zk SNARK works, for the equation above, we know two answers are (1,4), (2,30), we use (1,4) in this example.

Procedure

1. Write circuit, compile circuit
2. Generate PK(proving key) and VK(verifying key), export verifier contract(We're going to verify on blockchain), this contract contains VK.
3. Generate witness
4. Generate proof by PK and witness
5. Deploy verifier contract on chain
6. Verify on chain by proof

Steps

1. Build example:

   make build
   

2. Generate PK, VK, verifier contract, proof:

   build/zk-example
   

3. Deploy verifier contract and verify on chain:

   cd solidity && npm install
   npx hardhat test
   

   Output:

   Compiled 1 Solidity file successfully
   
   
     Verifier contract
   input:  [ 4 ]
   Verify result:  true
   	✔ Verify should success (1486ms)
   input:  [ 5 ]
   Verify result:  false
   	✔ Verify should fail (274ms)
   
   
     2 passing (2s)
   

You can use other x,y to test this micro zk system, like (2,30), (3,120) by running:

build/zk-example -x 2 -y 30
cd solidity && npx hardhat test