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Outline

• library VerifySignaturePool02
•    - function getMessageHash(
•    - function getEthSignedMessageHash(byte ...
•    - function verify(
•    - function recoverSigner(bytes32 _ethSi ...
•    - function splitSignature(bytes memory ...

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/**
 *Submitted for verification at Etherscan.io on 2022-06-30
*/

// SPDX-License-Identifier: MIT
pragma solidity 0.8.3;

/* Signature Verification

How to Sign and Verify
# Signing
1. Create message to sign
2. Hash the message
3. Sign the hash (off chain, keep your private key secret)

# Verify
1. Recreate hash from the original message
2. Recover signer from signature and hash
3. Compare recovered signer to claimed signer
*/

library VerifySignaturePool02 {
    /* 1. Unlock MetaMask account
    ethereum.enable()
    */

    /* 2. Get message hash to sign
    getMessageHash(
        0x14723A09ACff6D2A60DcdF7aA4AFf308FDDC160C,
        123,
        "coffee and donuts",
        1
    )

    hash = "0xcf36ac4f97dc10d91fc2cbb20d718e94a8cbfe0f82eaedc6a4aa38946fb797cd"
    */
    function getMessageHash(
        address nft,
        uint tokenID,
        uint valuation,
        uint expireAtBlock
    ) public pure returns (bytes32) {
        return keccak256(abi.encodePacked(nft, tokenID, valuation, expireAtBlock));
    }

    /* 3. Sign message hash
    # using browser
    account = "copy paste account of signer here"
    ethereum.request({ method: "personal_sign", params: [account, hash]}).then(console.log)

    # using web3
    web3.personal.sign(hash, web3.eth.defaultAccount, console.log)

    Signature will be different for different accounts
    0x993dab3dd91f5c6dc28e17439be475478f5635c92a56e17e82349d3fb2f166196f466c0b4e0c146f285204f0dcb13e5ae67bc33f4b888ec32dfe0a063e8f3f781b
    */
    function getEthSignedMessageHash(bytes32 _messageHash)
        public
        pure
        returns (bytes32)
    {
        /*
        Signature is produced by signing a keccak256 hash with the following format:
        "\x19Ethereum Signed Message\n" + len(msg) + msg
        */
        return
            keccak256(
                abi.encodePacked("\x19Ethereum Signed Message:\n32", _messageHash)
            );
    }

    /* 4. Verify signature
    signer = 0xB273216C05A8c0D4F0a4Dd0d7Bae1D2EfFE636dd
    to = 0x14723A09ACff6D2A60DcdF7aA4AFf308FDDC160C
    amount = 123
    message = "coffee and donuts"
    nonce = 1
    signature =
        0x993dab3dd91f5c6dc28e17439be475478f5635c92a56e17e82349d3fb2f166196f466c0b4e0c146f285204f0dcb13e5ae67bc33f4b888ec32dfe0a063e8f3f781b
    */
    function verify(
        address nft,
        uint tokenID,
        uint valuation,
        uint expireAtBlock,
        address _signer,
        bytes memory signature
    ) public pure returns (bool) {
        bytes32 messageHash = getMessageHash(nft, tokenID, valuation, expireAtBlock);
        bytes32 ethSignedMessageHash = getEthSignedMessageHash(messageHash);

        return recoverSigner(ethSignedMessageHash, signature) == _signer;
    }

    function recoverSigner(bytes32 _ethSignedMessageHash, bytes memory _signature)
        internal
        pure
        returns (address)
    {
        (bytes32 r, bytes32 s, uint8 v) = splitSignature(_signature);

        return ecrecover(_ethSignedMessageHash, v, r, s);
    }

    function splitSignature(bytes memory sig)
        internal
        pure
        returns (
            bytes32 r,
            bytes32 s,
            uint8 v
        )
    {
        require(sig.length == 65, "invalid signature length");

        assembly {
            /*
            First 32 bytes stores the length of the signature

            add(sig, 32) = pointer of sig + 32
            effectively, skips first 32 bytes of signature

            mload(p) loads next 32 bytes starting at the memory address p into memory
            */

            // first 32 bytes, after the length prefix
            r := mload(add(sig, 32))
            // second 32 bytes
            s := mload(add(sig, 64))
            // final byte (first byte of the next 32 bytes)
            v := byte(0, mload(add(sig, 96)))
        }

        // implicitly return (r, s, v)
    }
}

• No Contract Security Audit Submitted- Submit Audit Here

[{"inputs":[{"internalType":"bytes32","name":"_messageHash","type":"bytes32"}],"name":"getEthSignedMessageHash","outputs":[{"internalType":"bytes32","name":"","type":"bytes32"}],"stateMutability":"pure","type":"function"},{"inputs":[{"internalType":"address","name":"nft","type":"address"},{"internalType":"uint256","name":"tokenID","type":"uint256"},{"internalType":"uint256","name":"valuation","type":"uint256"},{"internalType":"uint256","name":"expireAtBlock","type":"uint256"}],"name":"getMessageHash","outputs":[{"internalType":"bytes32","name":"","type":"bytes32"}],"stateMutability":"pure","type":"function"},{"inputs":[{"internalType":"address","name":"nft","type":"address"},{"internalType":"uint256","name":"tokenID","type":"uint256"},{"internalType":"uint256","name":"valuation","type":"uint256"},{"internalType":"uint256","name":"expireAtBlock","type":"uint256"},{"internalType":"address","name":"_signer","type":"address"},{"internalType":"bytes","name":"signature","type":"bytes"}],"name":"verify","outputs":[{"internalType":"bool","name":"","type":"bool"}],"stateMutability":"pure","type":"function"}]

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ipfs://bf77a0dea2cbcc6ff0d21be1c162d5f7e56a512ed09814937cf5b2bb8614dea4