Understanding Metamask’s Signal Data Display in Viem

When using MetaMask for signature retrieval in a smart contract written in Solidity, it may display incorrect or unexpected character combinations such as Unicode question marks and other symbols. This phenomenon occurs when the Ethereum Virtual Machine (EVM) encounters an invalid or malformed signature.

The Problem: Incorrect Signal Signature Format

In Ethereum 2.0, the EVM introduced changes to the signature format, which requires a specific structure for signal 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 signal data format: EVM expects a specific hexadecimal format for signal data, while Viem may be using an alternative representation.

• Missing verification: Metamask may 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:

• Check the format of your signal data

  

  : Make sure 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 your contract logic.

• Displaying signal data correctly in Metamask

In Viem, make sure your signature is displayed correctly by specifying the correct format for the signal data when calling the signData function:

const signer = await ethers.getSigner('0x...'); // Replace '0x...' with your actual signal 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 corrected example displays the token data in hexadecimal format using ethers.utils.hexify(). You can adjust this to match the signature format of your specific contract.

Additional Tips and Considerations

• Ensure that your Solidity contract is well structured, with proper error handling and validation.

• Ensure that your Ethereum network (EVM) version matches the one required by Viem (e.g. Ethereum 2.0).

• If you are experiencing issues with signature retrieval on a specific blockchain or network, please refer to MetaMask’s documentation and support resources for more detailed guidance.

By following these steps and considering the possible causes of incorrect signature data displays in Metamask, you should be able to resolve this issue and successfully retrieve signer information in Viem.