Understanding Metamask’s Sign Data Display in Viem
When using MetaMask for signature recovery in a smart contract written in Solidity, it can display incorrect or unexpected character combinations as Unicode question marks and other symbols. This phenomenon occurs when the Ethereum Virtual Machine (EVM) encounters an invalid or malformed signature.
The Issue: Incorrect Sign Signature Format
In Ethereum 2.0, the EVM has introduced changes to the signature format, which requires a specific structure for the signature data. The correct format is represented by the hexadecimal 0x...
. However, when signing a message with MetaMask in Viem, it displays incorrect or missing characters in the signData
field.
Why Does Metamask Display Unicode Question Marks?
The displayed Unicode question marks (?
) are likely due to the following reasons:
- Incompatible Sign Data Format: The EVM expects a specific hexadecimal format for sign data, whereas Viem may be using an alternative representation.
- Lack of Verification: Metamask might not perform proper verification of the signature data before displaying it in the pop-up window.
Fixing the Issue: Correct Signature Format and Verification
To resolve this issue, follow these steps:
- Verify Your Sign Data Format: Ensure that your contract’s
signData
function returns a string containing only hexadecimal characters (e.g.,0x...
). If it contains other characters or non-hexadecimal data, you may need to adjust the contract logic.
- Correctly Displaying Sign Data in Metamask
In Viem, ensure that your signature is displayed correctly by specifying the correct format for sign data when calling the signData
function:
const signer = await ethers.getSigner('0x...'); // Replace '0x...' with your actual sign data
const tx = {
data: signer.signTransaction({
roof,
value: Wei.toWei(amount, 'ether'),
gas: Math.min(400000, (2 * gasLimit) + 100),
gasPrice: ethers.utils.parseUnits(gasPrice, 'web'),
}),
};
const encodedTx = tx.rawTransaction;
console.log(encodedTx);
This corrected example displays the sign data in hexadecimal format using ethers.utils.hexify()
. You can adjust this to match your specific contract’s signature format.
Additional Tips and Considerations
- Ensure that your Solidity contract is well-structured, with proper error handling and validation.
- Verify that your Ethereum network version (EVM) matches the one required by Viem (e.g., Ethereum 2.0).
- If you’re experiencing issues with signature recovery on a specific blockchain or network, consult MetaMask’s documentation and support resources for more detailed guidance.
By following these steps and considering the potential causes of incorrect sign data displays in Metamask, you should be able to resolve this issue and successfully recover signer information in Viem.