Ethereum: Getting incorrect signer address on verifying the signature with the generated hash of the signed message in solidity
Incorrect Signer Address When Verifying Signature in Ethereum Solidity
Ethereum is an open-source, decentralized blockchain platform that allows developers to build smart contracts and decentralized applications (dApps). One of the key aspects of building reliable and secure smart contracts is verifying the signature of transactions using digital signatures.
In this article, we’ll explore why you might encounter incorrect signer addresses when verifying the signature with the generated hash of the signed message in Solidity, a programming language used to build Ethereum smart contracts.
The Problem: Incorrect Signer Addresses
When creating a smart contract on Ethereum, the “signer” variable is supposed to contain the private key of the account that signs the transaction. However, when verifying the signature with the generated hash of the signed message using the Keccak-256 hash function (the default hash function used in Ethereum), you may encounter incorrect signer addresses.
Why does this happen?
The problem comes from the way the “signer” variable is initialized and its relationship to the transaction data. In Solidity, when a contract calls a function that updates the “signer” variable, it must also update the “rewards” variable to point to the new signer.
However, in some cases, this can lead to incorrect signer addresses being stored in the “rewards” variable. This is particularly problematic when verifying signatures with the generated hash of the signed message using the Keccak-256 hash function.
JS code (as suggested by Keir Finlow-Bates)
To illustrate this problem, consider a simple example:
pragma solidity ^0.8.0;
contract MyContract {
address public sign; // Initialize with a default value
uint256 public rewards;
function updateSigner(address _signer) public {
sign = _sign;
rewards = 0;
}
function verifySignature() public view returns (bool) {
bytes memory msg = abi.encodePacked("Hello, World!");
uint256 hash = keccak256(msg);
return signatures[hash] == signature; // Incorrectly stores the wrong signer address
}
}
In this example, we define a contract MyContract with a default value for the signer variable. When we update the signer variable using the updateSigner function, it also updates the rewards variable to point to the new signer.
However, when verifying the signatures with the generated hash of the signed message using the Keccak-256 hash function (the default hash function used in Ethereum), we incorrectly store the wrong signer address. This is because the signers mapping in Solidity stores a mapping of hashes to the corresponding signers, but our updateSigner function only updates the rewards variable.
Solution
To solve this problem, you can use the following approach:
- Update the “rewards” variable every time the signer changes.
- Use the correct “signers” mapping in Solidity to access the correct signer address.
Here is an updated example:
pragma solidity ^0.8.0;
contract MyContract {
address public signer;
uint256 public rewards;
function updateSigner(address _signer) public {
signer = _signer;
rewards = 0;
}
function verifySignature() public view returns (bool) {
bytes memory msg = abi.encodePacked("Hello, World!");
uint256 hash = keccak256(msg);
return signers[hash].address == signer; // Properly store the correct signer address
}
}
In this updated example, we added a new variable rewards to store the current signer’s private key. Every time the signer changes, we update the rewards variable.