Sign In With Ethereum Tutorial

To sign in with Ethereum using MetaMask, we leverage the ERC-4361 specification, which enables Ethereum accounts to authenticate with off-chain services via a standardized message format.

This technology offers a self-custodial alternative to centralized identity providers (e.g., email/password logins). For Web3 applications, it enhances user experiences and empowers users to control their digital identities.

How Sign In With Ethereum Works

1. Message Presentation: The wallet displays a plaintext message for signing, including:

   • User’s Ethereum address
   • Requesting domain
   • Chain identifier
   • Nonce & issued-at timestamp
2. Signing: The message is signed using ERC-191 and sent to the relying party.
3. Verification: The relying party validates the signature and message content before granting access.
4. Optional Fields: Expiration time, resources, or request IDs may be added.
5. Data Fetching: The relying party can fetch blockchain data (e.g., balances, assets) tied to the address.

Sign In With Ethereum Example

Below is a boilerplate message format:

${domain} wants you to sign in with your Ethereum account:  
${address}  
${statement}  
URI: ${uri}  
Version: ${version}  
Chain ID: ${chainId}  
Nonce: ${nonce}  
Issued At: ${issuedAt}  

👉 Explore MetaMask integration examples

Demo Code Using Ethers.js

const connectAndSign = async () => {  
  const provider = new ethers.providers.Web3Provider(window.ethereum, 'any');  
  await provider.send("eth_requestAccounts", []);  
  const signer = provider.getSigner();  
  const message = `...`; // Construct message as above  
  const flatSignature = await signer.signMessage(message);  
  console.log('Signature:', flatSignature);  
};  

Output:

• flatSignature: A hexadecimal string (e.g., 0x0eb1...e2615).
• soliditySignature: Split into r, s, and v for on-chain verification.

Verifying Signatures

Smart Contract Example

// SPDX-License-Identifier: MIT  
pragma solidity >=0.8.0;  

contract Verify {  
  function verifySignature(  
    bytes32 _hashedMessage,  
    uint8 _v,  
    bytes32 _r,  
    bytes32 _s  
  ) public pure returns (address) {  
    bytes memory prefix = "\x19Ethereum Signed Message:\n32";  
    bytes32 prefixedHash = keccak256(abi.encodePacked(prefix, _hashedMessage));  
    return ecrecover(prefixedHash, _v, _r, _s);  
  }  
}  

👉 Learn more about signature security

FAQ

1. Is Sign-In with Ethereum secure?

Yes, but always verify messages in MetaMask before signing. Use testnet wallets for experimentation.

2. Can I recover lost credentials?

No. Self-custody means users alone manage access—no centralized recovery exists.

3. What’s the advantage over traditional logins?

Eliminates password breaches and phishing risks via cryptographic signing.

4. Are there adoption challenges?

Yes. Off-chain services must support ERC-4361, which is still emerging.

Pros and Cons

| Pros | Cons |
|-------------------------------------------|-------------------------------------------|
| ✅ Self-custodial identity control | ❌ Technical complexity for developers |
| ✅ High security (cryptographic proofs) | ❌ Limited off-chain service adoption |
| ✅ Standardized workflow | ❌ No credential recovery options |

Conclusion

Sign-In with Ethereum pioneers decentralized authentication, prioritizing user control and security. While adoption hurdles remain, its potential to redefine digital identity in Web3 is significant.

Ready to implement? Start with the provided code snippets and always prioritize security.

👉 Discover advanced Ethereum tools