Keccak256 – Troubleshooting String Comparison Failures

keccakstring

When trying to compare a string from storage to a string being passed into a function (memory), I am getting the following error when attempting to convert the memory string using keccak256(). What am I supposed to be doing differently?

TypeError: Invalid type for argument in function call. Invalid implicit conversion from string memory to bytes memory requested. This function requires a single bytes argument. Use abi.encodePacked(...) to obtain the pre-0.5.0 behaviour or abi.encode(...) to use ABI encoding.

Best Answer

You should first convert the strings to bytes using abi.encode():

pragma solidity 0.5.4;

contract Test {
    string public constant text = "Hello world!";

    function isEqualTo(string memory myString) public pure returns(bool) {
        return (keccak256(abi.encode(text)) == keccak256(abi.encode(myString)));
    }
}

Related Solutions

Keccak256 – How to Pass a String to be Hashed Using Keccak256

try this snipet

function bytes32ToString(bytes32 x) constant returns (string) {
    bytes memory bytesString = new bytes(32);
    uint charCount = 0;
    for (uint j = 0; j < 32; j++) {
        byte char = byte(bytes32(uint(x) * 2 ** (8 * j)));
        if (char != 0) {
            bytesString[charCount] = char;
            charCount++;
        }
    }
    bytes memory bytesStringTrimmed = new bytes(charCount);
    for (j = 0; j < charCount; j++) {
        bytesStringTrimmed[j] = bytesString[j];
    }
    return string(bytesStringTrimmed);
}

 function someFunction(bytes32 _string) returns(bool){
    bool result = false;
    bytes32 hashparameter = sha3(bytes32ToString(_string));
    bytes32 hashstring = sha3("hello");
    if(hashstring == hashparameter) {
        result = true;
    }

    return result;

}

the first function converts bytes32 to string then passes the result to hashing function. I've tried it gives true for "hello".

[Ethereum] How to generate keccak256(STRING,INTEGER) from Javascript

Simple convert your integer into base 16, and append to original string finally calculate hash. It will be same.

function solSha3 (...args) {
    args = args.map(arg => {
        if (typeof arg === 'string') {
            if (arg.substring(0, 2) === '0x') {
                return arg.slice(2)
            } else {
                return web3.toHex(arg).slice(2)
            }
        }

        if (typeof arg === 'number') {
            return leftPad((arg).toString(16), 64, 0)
        } else {
          return ''
        }
    })

    args = args.join('')

    return '0x' + web3.sha3(args, { encoding: 'hex' })
}

For more details refer Github link

Best Answer

Related Solutions

Keccak256 – How to Pass a String to be Hashed Using Keccak256

[Ethereum] How to generate keccak256(STRING,INTEGER) from Javascript

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