[Ethereum] Python keccak256 hash of uint8 array not matching solidity hash

contract-developmentkeccakpython

I have a function in a smart contract:

  function getNumberHash(uint8[] _numbers) constant public returns (bytes32) {
    return keccak256(_numbers);
}

When I pass [1,2,3,4,5] as the argument it returns:

"0": "bytes32: 0x5917e5a395fb9b454434de59651d36822a9e29c5ec57474df3e67937b969460c"

I have this Python script but it returns a different hash:

import sha3
import numpy as np

a = np.array([1, 2, 3, 4, 5], dtype=np.uint8)

k = sha3.keccak_256()
k.update(a)
print(k.hexdigest())

Which returns the following hash:

0x7d87c5ea75f7378bb701e404c50639161af3eff66293e9f375b5f17eb50476f4

Why aren't the two functions returning the same value since they are both uint8[] and using the same keccak256 algorithm? How can I resolve this issue?

Best Answer

Web3.soliditySha3() will give you the correct hash.

The underlying reason is that solidity 0-pads values in arrays, which you won't get by default in most implementations. web3.py has the convenience method just for this purpose.

In this example, you would use:

from web3 import Web3
hash = Web3.soliditySha3(['uint8[]'], [[1, 2, 3, 4, 5]])
assert hash.hex() == '0x5917e5a395fb9b454434de59651d36822a9e29c5ec57474df3e67937b969460c'

Related Solutions

[Ethereum] How to access the address of a contract created by another contract

Often the contract itself is going to need to store the address for future use. So just store the address in the contract as an attribute, and retrieve it from outside the contract using the usual methods (e.g. call to the default getter ABI if you declare it public scope), after the transaction has been completed: (note, untested pseudo code, but I've done similar stuff a few times)

contract ObjectFactory {
    Object public theObj;

    function createObject(string name) returns (address objectAddress) {
        theObj = address(new Object(name));
        return theObj;
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}

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".

Best Answer

Related Solutions

[Ethereum] How to access the address of a contract created by another contract

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

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