4

The documentation says that sha3 calculates the hash of the tightly packed arguments. Numbers seem to be converted to ASCII chars.

Consider using sha3(values) in Solidity with the type int8[3] values, and the Javascript array let values = [-1, 0, 1];, how can I calculate the web3.sha3(...) hash in Javascript to get the same result as in Solidity?

What I tried so far:

web3.sha3(values.map((x) => String.fromCharCode(x)).join(''))

Also, why are these two different:

> sha3([int8(-1), int8(0), int8(1)])
0x485d3017777c5ed1be9073116ba54b48f208c386ab83497d9c3a015a8382849e
> sha3(int8(-1), int8(0), int8(1))
0x8404dcb0a81bbb8eccbf96f10e1874b12380080d2143c02c8e44db200aaff384

I found this issue on Github, which doesn't seem to handle my case of negative numbers. Maybe I should convert to uint in Javascript?

4

I finally found the solution.

The function given in this issue was the starting point. To make it work with negative numbers, I had to change it to this:

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') {
            if (arg < 0) {
              return leftPad((arg >>> 0).toString(16), 64, 'F');
            }
            return leftPad((arg).toString(16), 64, 0);
        } else {
          return '';
        }
    });

    args = args.join('');

    return '0x' + web3.sha3(args, { encoding: 'hex' });
}
  • Thanks, really helped. Update: web3.sha3 to web3.utils.sha3 – Senju Jun 17 '19 at 15:42
0

if you can to specify the types of the values you're on the safe side

given the solidity function

    function getHash(
        bytes32 bidID,
        uint256 date,
        int256[] volumes_Wh,
        uint256[] prices_mCent) public view returns (bytes32) {
        return keccak256(abi.encodePacked(bidID, date, volumes_Wh, prices_mCent));
    }
  async function hashIt () => {
    const bid = {
       bidID: (() => {
         let s = ''
         const bytes = randombytes(32)
         for (let i = 0; i < 32; i++) {
           s += ('0' + (bytes[i] & 0xFF).toString(16)).slice(-2)
         }
         return s
       })(),
       date: (new Date()).getTime(),
       volumes_Wh: [111, 222, 333, 444, 555],
       prices_mCent: [111, 222, 333, 444, 555]
     }
    console.log(await bids.getHash(`0x${bid.bidID}`, bid.date, bid.volumes_Wh, bid.prices_mCent))
    console.log(web3.utils.soliditySha3(
      {t: "bytes32", v: `0x${bid.bidID}`},
      {t: "uint256", v: bid.date},
      ... bid.volumes_Wh.map(vol => ({t: "int256", v: vol})),
      ... bid.prices_mCent.map(price => ({t: "uint256", v: price}))
    ).toString('hex'))
    assert.equal(true, true)
  }

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