Revolutionizing CrossChain KYC: Elevate Trust with Chainlink Functions and Hypersign DID for Enhanced Privacy and Zero-Knowledge Proof KYC

Problem Statement

In a Cross-chain Zero-Knowledge Proof KYC (ZK-KYC) verification system where the Issuer and Verifier operate on separate blockchains, the challenge is to ensure that when a user submits their proof to the Verifier Smart Contract, the contract can validate the legitimacy of the proof and confirm its origin and issuer's attestation from another blockchain, essentially verifying that the user possesses valid credentials issued by the authorized entity.

The Solution

To address the challenge of verifying the Issuer's attestation for the submitted ZK-Proof, we can leverage Chainlink Functions. This allows the Verifier Contract on the EVM Chain to confirm the Issuer's attestation for the submitted proof on the Hypersign ID chain. The process can be visualized through the following simplified diagram.

Flow Diagram

Sequence Diagram

From the above diagram, at a high level, these are the steps:

• User Submission: The user submits their Zero-Knowledge Proof to the Business Smart Contract on the EVM chain as a Verifiable Presentation (VP).
• Proof Attestation Check(Cross-chain):
  • The Business Contract on the EVM Chain utilizes Chainlink Functions to verify the Issuer's attestation from the Hypersign Chain for the submitted Verifiable Presentation.
  • This verification is achieved by calling the Hypersign ID Network from the Business Contract to confirm that the ZK-Proof is associated with a valid credential issued by the authorized Issuer.
• ZK-Proof Authenticity Check:
  • Following the successful verification of the Verifiable Presentation (VP) using Chainlink functions, the Business Contract proceeds to check the authenticity of the ZK-Proof.
  • This involves validating the ZK-Proof by interacting with the Verifier Smart Contract on the EVM Chain.

Solidity Business Contract

pragma solidity 0.8.19;

import {FunctionsClient} from "@chainlink/contracts/src/v0.8/functions/dev/v1_0_0/FunctionsClient.sol";
import {ConfirmedOwner} from "@chainlink/contracts/src/v0.8/shared/access/ConfirmedOwner.sol";
import {FunctionsRequest} from "@chainlink/contracts/src/v0.8/functions/dev/v1_0_0/libraries/FunctionsRequest.sol";
import {Groth16Verifier} from "Groth16Verifier.sol";

contract FunctionsConsumerExample is FunctionsClient, ConfirmedOwner {
    using FunctionsRequest for FunctionsRequest.Request;

    bytes32 public s_lastRequestId;
    bytes public s_lastResponse;
    bytes public s_lastError;

    error UnexpectedRequestID(bytes32 requestId);

    event Response(bytes32 indexed requestId, bytes response, bytes err);

    constructor(
        address router
    ) FunctionsClient(router) ConfirmedOwner(msg.sender) {}

    /**
     * @notice Send a simple request
     * @param source JavaScript source code
     * @param encryptedSecretsUrls Encrypted URLs where to fetch user secrets
     * @param donHostedSecretsSlotID Don hosted secrets slotId
     * @param donHostedSecretsVersion Don hosted secrets version
     * @param args List of arguments accessible from within the source code
     * @param bytesArgs Array of bytes arguments, represented as hex strings
     * @param subscriptionId Billing ID
     */
    function sendRequest(
        string memory source,
        bytes memory encryptedSecretsUrls,
        uint8 donHostedSecretsSlotID,
        uint64 donHostedSecretsVersion,
        string[] memory args,
        bytes[] memory bytesArgs,
        uint64 subscriptionId,
        uint32 gasLimit,
        bytes32 donID
    ) external onlyOwner returns (bytes32 requestId) {
        FunctionsRequest.Request memory req;
        req.initializeRequestForInlineJavaScript(source);
        if (encryptedSecretsUrls.length > 0)
            req.addSecretsReference(encryptedSecretsUrls);
        else if (donHostedSecretsVersion > 0) {
            req.addDONHostedSecrets(
                donHostedSecretsSlotID,
                donHostedSecretsVersion
            );
        }
        if (args.length > 0) req.setArgs(args);
        if (bytesArgs.length > 0) req.setBytesArgs(bytesArgs);
        s_lastRequestId = _sendRequest(
            req.encodeCBOR(),
            subscriptionId,
            gasLimit,
            donID
        );
        return s_lastRequestId;
    }

    /**
     * @notice Send a pre-encoded CBOR request
     * @param request CBOR-encoded request data
     * @param subscriptionId Billing ID
     * @param gasLimit The maximum amount of gas the request can consume
     * @param donID ID of the job to be invoked
     * @return requestId The ID of the sent request
     */
    function sendRequestCBOR(
        bytes memory request,
        uint64 subscriptionId,
        uint32 gasLimit,
        bytes32 donID
    ) external onlyOwner returns (bytes32 requestId) {
        s_lastRequestId = _sendRequest(
            request,
            subscriptionId,
            gasLimit,
            donID
        );
        return s_lastRequestId;
    }

    /**
     * @notice Store latest result/error
     * @param requestId The request ID, returned by sendRequest()
     * @param response Aggregated response from the user code
     * @param err Aggregated error from the user code or from the execution pipeline
     * Either response or error parameter will be set, but never both
     */
    function fulfillRequest(
        bytes32 requestId,
        bytes memory response,
        bytes memory err
    ) internal override {
        if (s_lastRequestId != requestId) {
            revert UnexpectedRequestID(requestId);
        }
        s_lastResponse = response;
        s_lastError = err;
        emit Response(requestId, s_lastResponse, s_lastError);
    }

    /**
     * @notice Verify the proof with the provided parameters
     * @param lastRequestId The last request ID to be verified
     * @param lastResponse The last response to be verified
     * @param a Groth16 proof parameter a
     * @param b Groth16 proof parameter b
     * @param c Groth16 proof parameter c
     * @param pubSignals Groth16 proof parameter pubSignals
     * @return true if the verification is successful, false otherwise
     */
    function callVerifyProof(
        bytes32 lastRequestId,
        bytes memory lastResponse,
        uint256[2] memory a,
        uint256[2][2] memory b,
        uint256[2] memory c,
        uint256[1] memory pubSignals
    ) external view returns (bool) {
        // Verify that the provided lastRequestId and lastResponse match the last stored values
        if (lastRequestId != s_lastRequestId || keccak256(lastResponse) != keccak256(s_lastResponse)) {
            return false;
        }

        // Replace verifierContractAddress with the actual address
        address verifierContractAddress = 0x7D5a9AbD3cCf6f68E5DE15968Bc56e13c4014dfF;
        Groth16Verifier verifierContract = Groth16Verifier(verifierContractAddress);

        // Call the verifyProof function with the provided parameters
        return verifierContract.verifyProof(a, b, c, pubSignals);
    }
}

The Above Contract utilizes method (verifyProof) from Verifier Contract

Verifier Contract

/*
    Copyright 2021 0KIMS association.

    This file is generated with [snarkJS](https://github.com/iden3/snarkjs).

    snarkJS is a free software: you can redistribute it and/or modify it
    under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    snarkJS is distributed in the hope that it will be useful, but WITHOUT
    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
    or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public
    License for more details.

    You should have received a copy of the GNU General Public License
    along with snarkJS. If not, see <https://www.gnu.org/licenses/>.
*/

pragma solidity 0.8.19;

contract Groth16Verifier {
    // Scalar field size
    uint256 constant r    = 21888242871839275222246405745257275088548364400416034343698204186575808495617;
    // Base field size
    uint256 constant q   = 21888242871839275222246405745257275088696311157297823662689037894645226208583;

    // Verification Key data
    uint256 constant alphax  = 20576316776612924346131171332485464798610324640807048645048471250491423249808;
    uint256 constant alphay  = 10642321740096627355850648777723082240829111043345624215090424286630925494357;
    uint256 constant betax1  = 17947706965765917029482593246351965150489707290959997966664783166885717332715;
    uint256 constant betax2  = 4889639933616333759066497113977711530404971799610976181222952679927065289829;
    uint256 constant betay1  = 19388018702326609682848109091973823137189678386603309310904895349692854321785;
    uint256 constant betay2  = 15386384629106652049512444335083778535780135974787835781550142520718813762980;
    uint256 constant gammax1 = 11559732032986387107991004021392285783925812861821192530917403151452391805634;
    uint256 constant gammax2 = 10857046999023057135944570762232829481370756359578518086990519993285655852781;
    uint256 constant gammay1 = 4082367875863433681332203403145435568316851327593401208105741076214120093531;
    uint256 constant gammay2 = 8495653923123431417604973247489272438418190587263600148770280649306958101930;
    uint256 constant deltax1 = 20171323842697838903468403858396180174522494776021316822393088588981861629214;
    uint256 constant deltax2 = 13732142793394296291229804888782706296790626209524502255609481659795712982286;
    uint256 constant deltay1 = 5556707875462008873377836417863099291510935535304624988913336419860749466809;
    uint256 constant deltay2 = 4429918161404727072954335103151854931705172565105190309702988967904406281635;

    
    uint256 constant IC0x = 7152929021430550769973796127968788866470553429782333352910886686307838422742;
    uint256 constant IC0y = 1080199901671684530575089418681939656424262882272933843925127815412640029839;
    
    uint256 constant IC1x = 5431969170227191688007020061682773133604136397111217701616128698575424669090;
    uint256 constant IC1y = 2138272652831160581537903944095797363742914109594667877446295841836321600072;
    
 
    // Memory data
    uint16 constant pVk = 0;
    uint16 constant pPairing = 128;

    uint16 constant pLastMem = 896;

    function verifyProof(uint[2] calldata _pA, uint[2][2] calldata _pB, uint[2] calldata _pC, uint[1] calldata _pubSignals) public view returns (bool) {
        assembly {
            function checkField(v) {
                if iszero(lt(v, q)) {
                    mstore(0, 0)
                    return(0, 0x20)
                }
            }
            
            // G1 function to multiply a G1 value(x,y) to value in an address
            function g1_mulAccC(pR, x, y, s) {
                let success
                let mIn := mload(0x40)
                mstore(mIn, x)
                mstore(add(mIn, 32), y)
                mstore(add(mIn, 64), s)

                success := staticcall(sub(gas(), 2000), 7, mIn, 96, mIn, 64)

                if iszero(success) {
                    mstore(0, 0)
                    return(0, 0x20)
                }

                mstore(add(mIn, 64), mload(pR))
                mstore(add(mIn, 96), mload(add(pR, 32)))

                success := staticcall(sub(gas(), 2000), 6, mIn, 128, pR, 64)

                if iszero(success) {
                    mstore(0, 0)
                    return(0, 0x20)
                }
            }

            function checkPairing(pA, pB, pC, pubSignals, pMem) -> isOk {
                let _pPairing := add(pMem, pPairing)
                let _pVk := add(pMem, pVk)

                mstore(_pVk, IC0x)
                mstore(add(_pVk, 32), IC0y)

                // Compute the linear combination vk_x
                
                g1_mulAccC(_pVk, IC1x, IC1y, calldataload(add(pubSignals, 0)))
                

                // -A
                mstore(_pPairing, calldataload(pA))
                mstore(add(_pPairing, 32), mod(sub(q, calldataload(add(pA, 32))), q))

                // B
                mstore(add(_pPairing, 64), calldataload(pB))
                mstore(add(_pPairing, 96), calldataload(add(pB, 32)))
                mstore(add(_pPairing, 128), calldataload(add(pB, 64)))
                mstore(add(_pPairing, 160), calldataload(add(pB, 96)))

                // alpha1
                mstore(add(_pPairing, 192), alphax)
                mstore(add(_pPairing, 224), alphay)

                // beta2
                mstore(add(_pPairing, 256), betax1)
                mstore(add(_pPairing, 288), betax2)
                mstore(add(_pPairing, 320), betay1)
                mstore(add(_pPairing, 352), betay2)

                // vk_x
                mstore(add(_pPairing, 384), mload(add(pMem, pVk)))
                mstore(add(_pPairing, 416), mload(add(pMem, add(pVk, 32))))


                // gamma2
                mstore(add(_pPairing, 448), gammax1)
                mstore(add(_pPairing, 480), gammax2)
                mstore(add(_pPairing, 512), gammay1)
                mstore(add(_pPairing, 544), gammay2)

                // C
                mstore(add(_pPairing, 576), calldataload(pC))
                mstore(add(_pPairing, 608), calldataload(add(pC, 32)))

                // delta2
                mstore(add(_pPairing, 640), deltax1)
                mstore(add(_pPairing, 672), deltax2)
                mstore(add(_pPairing, 704), deltay1)
                mstore(add(_pPairing, 736), deltay2)


                let success := staticcall(sub(gas(), 2000), 8, _pPairing, 768, _pPairing, 0x20)

                isOk := and(success, mload(_pPairing))
            }

            let pMem := mload(0x40)
            mstore(0x40, add(pMem, pLastMem))

            // Validate that all evaluations ∈ F
            
            checkField(calldataload(add(_pubSignals, 0)))
            
            checkField(calldataload(add(_pubSignals, 32)))
            

            // Validate all evaluations
            let isValid := checkPairing(_pA, _pB, _pC, _pubSignals, pMem)

            mstore(0, isValid)
             return(0, 0x20)
         }
     }
 }

TODO

Note

Note: If you want to run this project in local environment then reach out to the Hypersign Team for integration Discord

1. Hypersign API

[Optional] To use Hypersign API you can create app in Hypersign Entity Studio, by following the below instructions.

• Visit https://entity.hypersign.id/#/studio/dashboard
• Create App and keep the app app secret Key with you.
• Learn about the Hypersign API visit the doc here https://docs.hypersign.id/entity-studio/api-doc
• You can also try API Playground swagger implementation here for Hypersign API. https://api.entity.hypersign.id/api

2. Chainlink Functions

• Learn Chainlink Functions Doc https://docs.chain.link/chainlink-functions
• Open Remix IDE and create file called FunctionsConsumerExample.sol and pate above Solidity Business Contract.
• Make sure you have installed Metamsk in the browser and connect it to Remix IDE.
• Deploy the contract with router address - 0xb83E47C2bC239B3bf370bc41e1459A34b41238D0 on Sepolia Network.
• You can learn about supported networks router addresses in chainlink-supported doc.
• Copy the deployed Contract address and navigate to the chainlink subscription manager to fund the deployed contract with chainlink tokens. Follow instructions on this page
• Once the subscription is created and fund with chainlink tokens. Copy the Consumer Address and Subscription Id.
• No need to deploy Zk Verifier contract as it is deployed already for sepolia network

3. Clone the below repository

https://github.com/hypersign-protocol/dodo-wallet.git

• Checkout to chainlink-zk-kyc Branch

• Do npm install (Required node version would be 14.21 or above)

• After installing the dependencies

• Do npm run dev If you face an error regarding javascript heap memory out then run the below command

  NODE_OPTIONS=--max_old_space_size=4096 npm run dev

• Open the browser and navigate to http://localhost:9002

• Install Metamask Wallet Extension to the browser if you don't have one.

  https://metamask.io/download/

Demo Video

1. Understanding Problem Statement and Solution Video-1

2. Demo Implementation Video-2