transfer hash verification on contract side

Question

I want to verify if message-hash has a particular contract method.

Like below web3 code generates a rawTransaction having,messageHash,v, r, s, rawTransaction

let rawTransaction = {
        'from': fromAddress,
        'gasLimit': web3js.utils.toHex(310000),
        'to': contractAddress,
        'gasPrice': web3js.utils.toHex(20 * 1e9),
        'value': "0x0",
        'data': contract.methods.transfer(toAddress, amount).encodeABI(),
        'nonce': web3js.utils.toHex(count),
    }
  web3js.eth.accounts.signTransaction(rawTransaction, PK);

i.e if message hash from the above signed transaction is 0x9de6f7321d6374c8e26a1cd043daa71719175af97ed0f098260bf117db48dcbf

How can I create same hash in contract by passing above data for verification that given transaction hash is for transfer with all given values?

I have tried keccak256(abi.encodePacked()) using above data but it is generating different hash, may be I am doing something wrong.

Answer 1

Make sure of these 2 ponits:

1. While singing transaction, make sure to add leading 0x in the private key.
2. Add "\x19Ethereum Signed Message:\n32 before msg in the smart contract.

   bytes32 hash = keccak256(abi.encodePacked(
        "\x19Ethereum Signed Message:\n32",
        keccak256(abi.encodePacked(_data)))   
   )