Signature Mismatch In Hedera Wallet Connect: A Solution

by Alex Johnson 56 views

Understanding the Signature Mismatch Issue in Hedera Wallet Connect

When working with blockchain technologies like Hedera, ensuring the integrity and security of transactions is paramount. One common challenge developers face is a signature mismatch between the frontend and backend when using the sign(...) function with Hedera Wallet Connect. This issue can lead to failed transactions, security vulnerabilities, and a frustrating debugging experience. In this comprehensive guide, we'll delve into the intricacies of this problem, explore potential causes, and provide a step-by-step solution to resolve it effectively.

The signature mismatch typically arises from inconsistencies in how the message is prepared for signing on the frontend and how it's verified on the backend. These inconsistencies can stem from various factors, including differences in hashing algorithms, message formatting, or even subtle variations in the libraries used for cryptographic operations. To effectively troubleshoot this issue, it's crucial to understand the underlying cryptographic principles and the specific requirements of the Hedera network.

Key areas to investigate when facing a signature mismatch:

  1. Hashing Algorithms: Ensure that both the frontend and backend use the same hashing algorithm (e.g., Keccak-256) to generate the message digest. Discrepancies in the hashing algorithm will inevitably lead to signature mismatches.
  2. Message Formatting: Pay close attention to how the message is formatted before hashing. This includes encoding (e.g., UTF-8), prefixing, and any other transformations applied to the message. Inconsistencies in message formatting will result in different hash values and, consequently, signature mismatches.
  3. Library Versions: Ensure that the cryptographic libraries used on the frontend and backend are compatible and up-to-date. Outdated or incompatible libraries may have subtle differences in their implementation of cryptographic functions, leading to signature mismatches.
  4. Data Types: Verify that the data types used for cryptographic operations are consistent across the frontend and backend. For example, ensure that byte arrays are handled correctly and that there are no implicit type conversions that could alter the data.
  5. Asynchronous Operations: When dealing with asynchronous operations, such as signing messages with a wallet, ensure that the signing process is completed before attempting to verify the signature. Race conditions or incomplete signatures can lead to signature mismatches.

By carefully examining these areas, you can systematically identify the root cause of the signature mismatch and implement the necessary corrections.

Detailed Problem Breakdown

Let's analyze the provided code snippets to pinpoint the exact location of the signature mismatch. The frontend code uses ethers.keccak to hash the payload, while the backend code uses ethers.keccak256. Although both are Keccak-based hashing algorithms, ethers.keccak256 is the standard and recommended one. The frontend code then takes a slice .slice(2) after hashing, which removes the 0x prefix, and converts it into a Uint8Array. The backend code correctly hashes the message using ethers.keccak256 but introduces a prefix using the addPrefix function, which is crucial for Hedera's signing process.

The core issue lies in the discrepancy in how the message is prepared for signing on the frontend and backend. The frontend signs the raw Keccak hash, while the backend signs a Keccak hash with a Hedera-specific prefix and further hashes the prefixed message. This difference in the input to the signing process results in the signature mismatch.

Frontend Code Analysis:

  • Hashes the payload using ethers.keccak.
  • Slices the hash, removing the 0x prefix.
  • Converts the hash to a Uint8Array.
  • Signs the raw Keccak hash.

Backend Code Analysis:

  • Hashes the payload using ethers.keccak256.
  • Adds a Hedera-specific prefix to the message.
  • Hashes the prefixed message again using ethers.keccak256.
  • Signs the double-hashed, prefixed message.

The key difference is the prefixing and double-hashing step on the backend, which is not performed on the frontend. This discrepancy is the primary cause of the signature mismatch.

Step-by-Step Solution to Fix the Mismatch

To resolve the signature mismatch, we need to ensure that the message preparation steps on the frontend and backend are consistent. The most reliable approach is to align the frontend signing process with the backend's requirements, which include adding the Hedera-specific prefix and double-hashing the message.

Here's a detailed, step-by-step solution:

1. Modify the Frontend Code:

The frontend code needs to be updated to include the Hedera-specific prefix and double-hashing steps, mirroring the backend's process. This ensures that the message signed on the frontend is identical to the message expected by the backend for signature verification.

import { ethers } from 'ethers';

// Function to add a standard prefix to the message to be signed
const addPrefix = (input: Uint8Array): string => {
    return ethers.concat([
        ethers.toUtf8Bytes('\x19Hedera Signed Message:\n'),
        ethers.toUtf8Bytes(`${input.length}`),
        input
    ])
}

async function signMessage(payload: string, signer: any): Promise<string> {
    // 1. Hash the payload using keccak256
    const keccakHex = ethers.keccak256(ethers.toUtf8Bytes(payload)).slice(2);
    const keccak = Buffer.from(keccakHex, 'hex');

    // 2. Add the Hedera-specific prefix
    const keccakPrefixed = addPrefix(new Uint8Array(keccak));
    const keccakPrefixedHex = ethers.hexlify(keccakPrefixed).slice(2);

    // 3. Hash the prefixed message again
    const keccakPrefixedHashedHex = ethers.keccak256(keccakPrefixed);

    // 4. Sign the double-hashed, prefixed message
    const sig = (await signer.signMessage(ethers.getBytes(keccakPrefixedHashedHex)));

    return sig;
}

// Example usage:
const payload = 'Hello Hedera';
// Assuming signerZero is an ethers.Signer instance
// const sig = await signMessage(payload, signerZero!);
// console.log(sig); // Prints the signature

2. Ensure Consistent Hashing:

Both the frontend and backend should use ethers.keccak256 for hashing. This consistency is crucial for generating the same hash value from the same input message.

3. Verify Prefixing Logic:

Double-check the addPrefix function to ensure it correctly adds the Hedera-specific prefix to the message. The prefix includes the string \x19Hedera Signed Message:\n followed by the length of the message. Any discrepancy in this prefix will lead to a signature mismatch.

4. Test with the Same Payload:

Use the same payload (Hello Hedera in this case) for testing on both the frontend and backend. This eliminates any potential issues related to payload differences.

5. Inspect the Signature:

After implementing the changes, log the signature on both the frontend and backend to verify that they match. This is the ultimate confirmation that the signature mismatch issue has been resolved.

Comprehensive Code Example

To illustrate the solution, here's a comprehensive code example that incorporates the necessary changes on both the frontend and backend.

Frontend Code (TypeScript):

import { ethers } from 'ethers';

// Function to add a standard prefix to the message to be signed
const addPrefix = (input: Uint8Array): string => {
    return ethers.concat([
        ethers.toUtf8Bytes('\x19Hedera Signed Message:\n'),
        ethers.toUtf8Bytes(`${input.length}`),
        input
    ]);
};

async function signMessage(payload: string, signer: any): Promise<string> {
    // 1. Hash the payload using keccak256
    const keccakHex = ethers.keccak256(ethers.toUtf8Bytes(payload)).slice(2);
    const keccak = Buffer.from(keccakHex, 'hex');

    // 2. Add the Hedera-specific prefix
    const keccakPrefixed = addPrefix(new Uint8Array(keccak));
    const keccakPrefixedHex = ethers.hexlify(keccakPrefixed).slice(2);

    // 3. Hash the prefixed message again
    const keccakPrefixedHashedHex = ethers.keccak256(keccakPrefixed);

    // 4. Sign the double-hashed, prefixed message
    const sig = await signer.signMessage(ethers.getBytes(keccakPrefixedHashedHex));

    return sig;
}

// Example usage:
async function main() {
    const payload = 'Hello Hedera';
    // Replace with your actual signer
    const provider = new ethers.BrowserProvider(window.ethereum)
    const signer = await provider.getSigner()
    const sig = await signMessage(payload, signer);
    console.log('Frontend Signature:', sig);
}

main().catch(console.error);

Backend Code (TypeScript):

import { ethers } from 'ethers';

// Function to add a standard prefix to the message to be signed
const addPrefix = (input: Uint8Array): string => {
    return ethers.concat([
        ethers.toUtf8Bytes('\x19Hedera Signed Message:\n'),
        ethers.toUtf8Bytes(`${input.length}`),
        input
    ]);
};

async function verifySignature(payload: string, publicKeyHex: string, signature: string): Promise<boolean> {
    // 1. Hash the payload using keccak256
    const keccakHex = ethers.keccak256(ethers.toUtf8Bytes(payload)).slice(2);
    const keccak = Buffer.from(keccakHex, 'hex');

    // 2. Add the Hedera-specific prefix
    const keccakPrefixed = addPrefix(new Uint8Array(keccak));
    const keccakPrefixedHex = ethers.hexlify(keccakPrefixed).slice(2);

    // 3. Hash the prefixed message again
    const keccakPrefixedHashedHex = ethers.keccak256(keccakPrefixed);

    // 4. Recover the address from the signature
    const recoveredAddress = ethers.recoverAddress(keccakPrefixedHashedHex, signature);

    // 5. Convert the public key hex to an address
    const publicKey = ethers.computeAddress(`0x${publicKeyHex}`);

    // 6. Compare the recovered address with the public key
    return recoveredAddress.toLowerCase() === publicKey.toLowerCase();
}

// Example usage:
async function main() {
    const payload = 'Hello Hedera';
    const publicKeyHex = '302a300506032b65700321004c192b1e7959d2449d777af56f7243a217c4fc146972c641707b987c4a9e16c7'; // Replace with the actual public key
    const signature = '0x...'; // Replace with the signature from the frontend

    const isValid = await verifySignature(payload, publicKeyHex, signature);
    console.log('Signature is valid:', isValid);
}

main().catch(console.error);

This comprehensive code example demonstrates the complete process of signing a message on the frontend and verifying it on the backend, ensuring consistency in the message preparation steps.

Additional Tips for Debugging

If you continue to experience signature mismatches, consider the following additional debugging tips:

  • Log Intermediate Values: Log the intermediate values of the hash, prefixed message, and signature on both the frontend and backend. This helps identify any discrepancies in the message preparation process.
  • Use a Debugger: Use a debugger to step through the code and inspect the values of variables at each step. This can help pinpoint the exact location where the signature mismatch occurs.
  • Simplify the Payload: Start with a simple payload and gradually increase its complexity. This helps isolate any issues related to the payload itself.
  • Consult Documentation: Refer to the documentation for the specific libraries and tools you are using. The documentation may contain valuable information about signature generation and verification.

Conclusion

Signature mismatches in Hedera Wallet Connect can be a challenging issue, but by understanding the underlying causes and following a systematic approach to troubleshooting, you can effectively resolve them. The key is to ensure consistency in the message preparation steps on the frontend and backend, including using the same hashing algorithm, applying the Hedera-specific prefix, and double-hashing the message.

By implementing the solution outlined in this guide, you can ensure the integrity and security of your Hedera transactions and provide a seamless user experience.

For more information on Hedera and related technologies, visit the official Hedera Hashgraph website.