Lease demo

Lease demo with zero knowledge proofs

Installation

You need to install node and git. Then install circom:

curl --proto '=https' --tlsv1.2 https://sh.rustup.rs -sSf | sh
git clone https://github.com/iden3/circom.git
cargo build --release
cargo install --path circom
npm install -g snarkjs

Install hardhat that is used for solidity contracts

npm install --save-dev hardhat

and finally clone this repo

git clone https://github.com/Benjamin-Herald/lease
cd lease
yarn

Put config.js file with configuration into packages/config directory using template as example

Contracts

Contracts are deployed to Rinkeby network. Faucet is located at https://rinkebyfaucet.com/
Blockchain explorer is located at https://rinkeby.etherscan.io/

Equipment NFT contract tracks equipment owned by Lessors and Vendors.

Function buy on Equipment contract transfer ownership from Vendor to Lessor checking ZK proof proving that Lessor has enough money by using BuyVerifier contract:

	function buy(
		uint256 tokenId,
		uint[2] memory a,
		uint[2][2] memory b,
		uint[2] memory c,
		uint[2] memory input)
        public
    {
    	require( input[0] == 1, "not enough money to buy"); 
    	require( input[1] == price[tokenId] , "wrong price"); 
    	require( verifier.verifyProof(a, b, c, input) == true, "wrong proof");
    	
    	address tokenOwner = ownerOf(tokenId);
    	safeTransferFrom(tokenOwner, msg.sender, tokenId);
    
    }

Lease contract tracks equipment leased by Lessor to Lessee.

Function lease on this contract creates NFT with lease terms checking ZK proof proving that

• Lessee scoring is correct (using LeaseVerifier ZK contract)
• Lessor owns equipment being leased (using Equipment contract)

    function lease(address to, // Lessee address
                   string memory uri, 
                   uint256 _equipmentId,
                   uint[2] memory a,
                   uint[2][2] memory b,
                   uint[2] memory c,
                   uint[4] memory input) public 
	{
    	require( equipment.ownerOf(_equipmentId) == msg.sender, "not a owner of equipment"); 
    	require( verifier.verifyProof(a, b, c, input) == true, "wrong proof");
    	
        uint256 tokenId = _tokenIdCounter.current();
        _tokenIdCounter.increment();
        _safeMint(to, tokenId);
        _setTokenURI(tokenId, uri);
        equipmentId[tokenId] = _equipmentId;
    }

Equipment deployed to 0x49549aD4872Bb0F487eF8947FcdFCd0Af1479B71
Lease deployed to 0x68DB2cf0E076E3DDBdb66179760Da4a9BB232d33

LeaseVerifier deployed to: 0xa485e21B76CcF50841db2Cc31813113E26F66ec2
BuyVerifier deployed to: 0xe96f6f106091E6D4Fb09850bD81687c2ca9562CA

Usage with command line tools:

Purchase of equipment by Lessor from Vendor

Generating ZK proof by Lessor for Vendor proving that Lessor has cash on account enough to buy Equipment without disclosing amount of cash. Edit /data/lessor-data.json to input cash on account of Lessor and price of equipment set by Vendor and run

yarn preparebuy

Results of executing the circuit circuit/buy.circom will be in the data folder in buyproof.json and buypublic.json, first value in buypublic.json is boolean and indicates if cash is enough to buy equipment, second value is the price of equipment.

To verify ZK proof (both by calling BuyVerifier contract and by using snarkjs command line tool), run

yarn verifybuy

To actually transfer NFT from Vendor to Lessor run

yarn buy

To return NFT with equipment from Lessor to Vendor run

yarn return

Lease of equipment owned by Lessor to Lessee

Generating ZK proof with credit rating by Lessee for Lessor Edit /data/lessee-data.json to input data of Lessee and run

yarn preparelease

Results of executing the circuit circuit/lease.circom will be in the data folder in leaseproof.json and leasepublic.json, first value in leasepublic.json is Lessee's credit rating, second value is the roothash of SMT of Lessee's data from lessee-data.json, third is Lessee's Ethereum address and fourth is time

To verify ZK proof, run

yarn verifylease

To make offer from Lessor to Lessee taking into account rating of Lessee, run

yarn offer	

The result of the offer will be in data/offer.json

To accept the offer and mint NFT on Lease contract, run

yarn accept

There will be minted NFT like https://testnets.opensea.io/assets/0x68db2cf0e076e3ddbdb66179760da4a9bb232d33/0

NFT

Using as example Ultrasonido LOGIQ P9 (USD 19000)

https://xrgmed.com.mx/producto/logic-p9/

https://www.ultrasoundsupply.com/products/ultrasound-machines/ge-ultrasound/ge-logiq-p9/

Equipment NFTs: https://testnets.opensea.io/collection/equipment-9w1atiw3ed

Lease NFT: https://testnets.opensea.io/assets/0x68db2cf0e076e3ddbdb66179760da4a9bb232d33/0

TODO

• NFT and IPFS creation cli