Sign In With Ethereum Tutorial

Signing in with Ethereum is revolutionizing how users authenticate online by replacing traditional email and password logins with decentralized, blockchain-based identity verification. Built on the ERC-4361 standard, this method enables Ethereum wallet holders to securely prove ownership of their addresses without surrendering control to centralized platforms. This guide walks you through the mechanics, implementation, and best practices of Sign In With Ethereum (SIWE), empowering developers and users alike to embrace self-sovereign digital identity.

How Sign In With Ethereum Works

Sign In With Ethereum allows users to log in to web applications using their Ethereum wallet—no passwords required. The process follows a standardized message format defined by ERC-4361, ensuring consistency across platforms and improved security.

Here’s how it works:

1. Message Generation: When a user attempts to log in, the application generates a human-readable message containing key details such as:

   • The user’s Ethereum address
   • The requesting domain
   • Chain ID
   • Nonce (to prevent replay attacks)
   • Timestamp of issuance
2. User Signature: This message is sent to the user’s wallet (e.g., MetaMask), where they review and sign it using their private key. Because the message appears in plain text, users can clearly see what they’re approving.
3. Signature Submission: The signed message is sent back to the server or smart contract for verification.
4. Verification: The recipient validates the signature using cryptographic methods like ecrecover or libraries such as ethers.js, confirming that the message was indeed signed by the claimed address.
5. Access Granted: Upon successful verification, the user gains access to the service—authenticated without any third-party identity provider.

This entire flow supports optional fields like expiration time and resource URLs, enhancing flexibility for developers.

👉 Discover how blockchain authentication enhances security and user control

Implementing Sign In With Ethereum: Code Example

Below is a practical implementation using ethers.js, ideal for integrating SIWE into your dApp.

const provider = new ethers.providers.Web3Provider(window.ethereum, 'any');

const connectAndSign = async () => {
  await provider.send("eth_requestAccounts", []);
  const signer = provider.getSigner();

  const domain = 'example.com';
  const userAddress = await signer.getAddress();
  const statement = 'I accept the terms and wish to sign in with Ethereum';
  const uri = 'https://example.com/login';
  const version = '1';
  const chainId = await signer.getChainId();
  const nonce = Math.round(Math.random() * 9999999).toString();
  const issuedAt = new Date().toISOString();

  const message = `${domain} wants you to sign in with your Ethereum account:
${userAddress}
${statement}
URI: ${uri}
Version: ${version}
Chain ID: ${chainId}
Nonce: ${nonce}
Issued At: ${issuedAt}`;

  let flatSignature = await signer.signMessage(message);
  let soliditySignature = ethers.utils.splitSignature(flatSignature);

  console.log('Signature (flat):', flatSignature);
  console.log('Signature (structured):', soliditySignature);

  document.getElementById('output').innerHTML = flatSignature;

  // Send signature and message to backend for verification
};

This code snippet prompts the user to sign a structured message via MetaMask. It returns both a flat hexadecimal signature and a split format (r, s, v) suitable for on-chain verification.

Verifying Ethereum Signatures

Authentication isn’t complete without verification. You can validate signatures either on-chain via smart contracts or off-chain using backend services.

On-Chain Verification (Smart Contract)

Using Solidity, you can verify signatures directly within a contract:

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

contract Verify {
    function recoverSigner(
        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);
    }
}

This function recovers the original signer from the signature components, enabling trustless access control in decentralized applications.

Off-Chain Verification (Backend)

For traditional web servers, use libraries like ethers.js or web3.py to verify signatures before issuing session tokens.

👉 Learn how secure digital signatures protect user identity in Web3

Benefits of Sign In With Ethereum

Adopting SIWE brings several advantages over conventional authentication systems:

• Self-Custody Identity: Users retain full control of their credentials—no reliance on email providers or social logins.
• Enhanced Security: Cryptographic signing prevents phishing and credential theft.
• Interoperability: Standardized messaging improves compatibility across dApps and services.
• Improved UX: One-click login with transparent consent management enhances user experience.

Challenges and Considerations

Despite its promise, SIWE faces adoption hurdles:

• User Education: New users may struggle with signing messages versus familiar password inputs.
• Limited Adoption: Many mainstream platforms still rely on OAuth; widespread SIWE integration remains in progress.
• No Recovery Mechanism: Lost keys mean lost access—there's no "forgot password" option in self-custody systems.

Developers must design intuitive interfaces and educate users about safe signing practices.

Frequently Asked Questions (FAQ)

Q: What is Sign In With Ethereum (SIWE)?
A: SIWE is a decentralized authentication standard (ERC-4361) that lets users log in to apps using their Ethereum wallet instead of passwords.

Q: Is signing a SIWE message safe?
A: Yes—if you only sign on trusted sites and carefully review the message content in your wallet before approving.

Q: Can I use SIWE with any wallet?
A: Most EVM-compatible wallets like MetaMask, WalletConnect, and Coinbase Wallet support SIWE.

Q: Does SIWE work off-chain?
A: Yes—SIWE signatures can be verified by backend servers or smart contracts, making them ideal for hybrid Web2/Web3 applications.

Q: What happens if I lose my wallet?
A: Since SIWE relies on self-custody, there is no recovery option if you lose access to your private keys or seed phrase.

Q: How does SIWE improve privacy?
A: It reduces data exposure—no need to share emails or personal details with every service you join.

👉 Explore tools that support secure Ethereum-based login experiences

Final Thoughts

Sign In With Ethereum represents a foundational shift toward user-owned identity on the internet. By combining cryptographic security with standardized messaging, SIWE empowers individuals to interact with digital services without sacrificing autonomy. While challenges remain in education and adoption, the future of authentication lies in decentralization—and Ethereum is leading the way.

Whether you're building the next generation of dApps or simply exploring Web3 login options, understanding and implementing SIWE is a critical step forward in creating secure, user-centric experiences.