Create a EOA or SCW signer

This code defines two functions that convert different types of Ethereum accounts—Externally Owned Accounts (EOAs) and Smart Contract Wallets (SCWs)—into a unified Signer interface.

This ensures that both account types conform to a common interface for message signing and deriving shared secrets as per MLS (Message Layer Security) requirements. SigningKey now supports only one sign method: sign(signatureText: String): SignedData.

Create an EOA signer

For an EOA, the convertEOAToSigner function creates a signer that can get the account identity and sign messages and has placeholder methods for chain ID and block number.

Browser

import type { Signer } from "@xmtp/browser-sdk"; 
 
const accountIdentity = { 
  kind: "ETHEREUM", // Specifies the identity type 
  identifier: "0x...", // Ethereum address as the identifier 
}; 
 
const signer: Signer = { 
  getIdentity: () => accountIdentity, 
  signMessage: async (message) => { 
    // return value from a signing method here 
  }, 
};

Create an SCW signer

For an SCW, the convertSCWToSigner function similarly creates a signer but includes a specific implementation for chain ID and an optional block number computation.

Browser

import type { Signer } from "@xmtp/browser-sdk"; 
 
const accountIdentity = { 
  kind: "ETHEREUM", // Specifies the identity type 
  identifier: "0x...", // Smart Contract Wallet address 
}; 
 
const signer: Signer = { 
  getIdentity: () => accountIdentity, 
  signMessage: async (message) => { 
    // return value from a signing method here 
  }, 
  // These methods are required for smart contract wallets 
  getBlockNumber: () => undefined, // Optional block number 
  getChainId: () => BigInt(8453), // Example: Base chain ID 
};