Viem SIWE

This skill provides expertise in implementing Sign-In with Ethereum (SIWE) adhering to EIP-4361 using viem.

Reference Implementation

For a complete, copy-pasteable implementation of a SIWE auth module, refer to references/implementation.md.

This implementation includes:

• siwe.ts: Core logic for nonce generation, message creation, parsing, and verification.
• index.ts: Public API for the auth module.

API Documentation

For detailed API documentation of viem's SIWE utilities (createSiweMessage, verifySiweMessage, etc.), refer to references/api-docs.md.

Critical Implementation Details

Nonce Management

• Always generate a unique nonce for every login attempt.
• Store nonces with an expiration (TTL) on the backend.
• Verify and consume the nonce upon signature validation to prevent replay attacks.

Message Verification

• Verify Domain: Ensure the domain in the message matches the host to prevent phishing.
• Verify Chain ID: Ensure the chainId matches the expected network.
• Check Expiration: Respect expirationTime and notBefore fields.

Smart Contract Wallets (ERC-1271)

When verifying signatures from smart contract wallets:

• Use a PublicClient instance in verifySiweMessage.
• Do not rely solely on verifyMessage which only works for EOAs.