Incorrect signer address when verifying signature in Ethereum Solidity
Ethereum is an open-source, decentralized blockchain platform that allows developers to create 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 will explore why you may encounter incorrect signer addresses when verifying a signature using a generated hash of a signed message in Solidity, the programming language used to create Ethereum smart contracts.
Problem: Incorrect signer addresses
When creating a smart contract on Ethereum, the signer variable is expected to contain the private key of the account signing the transaction. However, when verifying a signature generated by a hash of a 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 arises in 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 should 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 generated by a hash of a signed message using the Keccak-256 hash function.
JS code (as suggested by Keira Finlow-Bates)
To illustrate this issue, let’s consider a simple example:
pragma strength^0.8.0;
contract MyContract {
public signer address; // Initialize with default value
public rewards uint256;
function updateSigner(_signer address) public {
signer = _signer;
rewards = 0;
}
function authenticSignature() public view returns (bool) {
bytes of memory msg = abi.encodePacked("Hello, world!");
uint256 hash = keccak256(msg);
return signs[hash] == signer; // Incorrectly storing the wrong signer address
}
}
In this example, we define a contract “MyContract” with a default value for the variable “signer”. When we update the variable `signer'' using theupdateSigner'' function, therewards'' variable is also updated to point to the new signer.
However, when verifying signatures with the generated hash of the signed message using the Keccak-256 hash function (the default hash function used in Ethereum), we are incorrectly storing the wrong signer address. This is because thesigners'' mapping in Solidity stores the mapping from the hash to the corresponding signers, but ourupdateSigner'' function only updates therewards'' variable.
Solution
To resolve this issue, you can use the following approach:
- Update the
rewards'' variable whenever the signer changes.
- Use the correct
signers'' mapping in Solidity to access the correct signer address.
Here is an updated example:
pragma strength^0.8.0;
contract MyContract {
public signer address;
public rewards uint256;
function updateSigner(_signer address) public {
signer = _signer;
rewards = 0;
}
function authenticSignature() public view returns (bool) {
bytes of memory msg = abi.encodePacked("Hello, world!");
uint256 hash = keccak256(msg);
return signers[hash].address == signer; // Correctly stores the correct signer address
}
}
In this updated example, we have added a new variable rewardsto store the private key of the current signer. Whenever the signer changes, we update therewards` variable.