Understanding MetaMask Sign Data Display in Viem
When using MetaMask to recover a signature in a smart contract written in Solidity, it may display invalid or unexpected character combinations as Unicode question marks and other symbols. This phenomenon occurs when the Ethereum Virtual Machine (EVM) encounters an invalid or improperly formatted signature.
Issue: Invalid Sign Data Format
In Ethereum 2.0, the EVM introduced changes to the signature format that require a specific structure for the sign data. The correct format is represented by hexadecimal 0x.... However, when signing a message using MetaMask in Viem, it displays invalid or missing characters in the signData field.
Why does Metamask display Unicode question marks?
The Unicode question marks (?) that are displayed are likely due to the following reasons:
- Incompatible character data format: EVM expects a specific hexadecimal format for the character data, while Viem may use an alternate representation.
- Lack of verification: Metamask may not properly verify the signature data before displaying it in the popup.
Troubleshooting: Valid signature format and verification
To resolve this issue, follow these steps:
- Verify the character data format: Make sure that your contract’s
signDatafunction returns a string containing only hexadecimal characters (e.g.0x...). If it contains other characters or non-hexadecimal data, you may need to adjust your contract logic.
- Properly displaying sign data in Metamask
In Viem, make sure the signature is displayed correctly by specifying the correct sign data format when calling the signData function:
const signer = await ethers.getSigner('0x...'); // Replace '0x...' with the actual sign data
const tx = {
data: signer.signTransaction({
to,
value: Wei.toWei(amount, 'ether'),
gas: Math.min(400000, (2 * gasLimit) + 100),
gasPrice: ethers.utils.parseUnits(gasPrice, 'gwei'),
}),
};
const encodedTx = tx.rawTransaction;
console.log(encodedTx);
This improved example displays the sign data in hexadecimal format using ethers.utils.hexify(). You can customize this to match your specific contract’s signature format.
Additional Tips and Notes
- Make sure your Solidity contract is well-structured, with proper error handling and validation.
- Check that your Ethereum network version (EVM) matches the version required by Viem (e.g. Ethereum 2.0).
- If you are having trouble recovering a signature on a specific blockchain or network, please refer to the MetaMask documentation and support resources for more detailed guidance.
By following these steps and considering the potential causes of incorrect sign data display in Metamask, you should be able to resolve the issue and successfully recover signer information in Viem.