C# how to compute Keccak256 to match Solidity?

Question

I have a simple Solidity function as below:

function testKeccak(uint8[] buffer) public pure returns (bytes32) {
    return keccak256(abi.encodePacked(buffer));
}

Testing the keccak256 hash using library from: https://github.com/modulexcite/CEX

But they yield different results.

var In = "54686973206973206A75737420612074657374"; // Assume this is a byte[], otherwise the code won't compile
Web3 w = new Web3("http://localhost:8545/");
Contract c = w.Eth.GetContract("My ABI", " My Contract Address");
var r = c.GetFunction("testKeccak").CallAsync<byte[]>(In).Result;

//Expected = 68D0D86DF8DCA7ABDAD4DA5986F7E33FA7637EE85775A64AE965E10E3841923E
//Received = FC3B317A9FB7A02E6FF7A1839EEA04A21C30D9CD15B3414FA7431F09DEEC9D9D

May I know if there is any C# library out there which can get the correct Keccak256 hash when compared to Solidity?

Answer 1

Tested:

using System;
using System.Linq;
using Org.BouncyCastle.Crypto.Digests;

namespace myNamespace
{
    public static class TransactionTool
    {
        public static string GetTransactionHash(string rawTransaction)
        {
            var offset = rawTransaction.StartsWith("0x") ? 2 : 0;

            var txByte = Enumerable.Range(offset, rawTransaction.Length - offset)
                             .Where(x => x % 2 == 0)
                             .Select(x => Convert.ToByte(rawTransaction.Substring(x, 2), 16))
                             .ToArray();

            //Note: Not intended for intensive use so we create a new Digest.
            //if digest reuse, prevent concurrent access + call Reset before BlockUpdate
            var digest = new KeccakDigest(256);

            digest.BlockUpdate(txByte, 0, txByte.Length);
            var calculatedHash = new byte[digest.GetByteLength()];
            digest.DoFinal(calculatedHash, 0);

            var transactionHash = BitConverter.ToString(calculatedHash, 0, 32).Replace("-", "").ToLower();

            return transactionHash;
        }
    }
}

Answer 2

I found that this C# lib implement keccak256

https://github.com/multiformats/cs-multihash

Answer 3

It is likely that there is a padding version mismatch. You can use https://www.nuget.org/packages/SHA3/1.0.0-rc to choose which padding version you'd like, the official SHA3 is now the default. Setting UseKeccakPadding to true enables original Keccak padding.