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Overview

Message signing allows you to apply a unique cryptographic signature to verify your identity on EVM networks. Using the CDP-SDK, developers can enable signing of messages with the EIP-191 standard, which prepends messages with a standard prefix before signing. This ensures messages are easily distinguishable from transaction data and provides a secure way to prove ownership of an address. In this guide, you will learn how to:
  • Create an EVM account
  • Sign a message using EIP-191 standard

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Prerequisites

It is assumed you have already completed the Quickstart guide.

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1. Create an account

To create an account, see below: 
import { CdpClient } from "@coinbase/cdp-sdk";
import "dotenv/config";
  
const cdp = new CdpClient();
  
const account = await cdp.evm.createAccount();
  
console.log("Successfully created account: ", account.address);
After running the above snippet, you should see output similar to the following: 
Successfully created account: 0x6aAEc7535706ce8B36ea184B2236D53702c1F06A

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2. Sign message

The v2 Server Wallet supports EIP-191 message signing, which provides a standardized way to sign messages on Ethereum. Per the specification, the message is prepended with \x19Ethereum Signed Message:\n followed by the message length before being signed.

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What is EIP-191?

EIP-191 is a standard for signing messages in Ethereum that helps prevent signed messages from being confused with signed transactions. It defines a structured format for signed data that includes:
  • A magic byte 0x19 to ensure the data could never be a valid RLP-encoded transaction
  • The string “Ethereum Signed Message:\n”
  • The length of the message
  • The actual message content

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Use Cases

EIP-191 signed messages are commonly used for:
  • Authentication: Proving ownership of an address without making a transaction
  • Off-chain agreements: Signing terms of service or other agreements
  • Message verification: Allowing others to verify that a specific address signed a message
  • Login systems: Implementing “Sign in with Ethereum” functionality

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Security Benefits

  • Messages cannot be replayed as transactions
  • Clear separation between transaction signing and message signing
  • Human-readable messages instead of raw hashes
  • Protection against phishing attacks by showing users what they’re signing
Here is a complete example showing how to sign a message using EIP-191: 
import { CdpClient } from "@coinbase/cdp-sdk";  
import "dotenv/config";  
  
const cdp = new CdpClient();
  
const account = await cdp.evm.createAccount();
console.log("Created account:", account.address);
  
const message = "Hello, Coinbase Developer Platform!";
const signature = await cdp.evm.signMessage({
  address: account.address,
  message
});
  
console.log("Message:", message);
console.log("Signature:", signature);

// The signature can be verified by anyone to prove the account signed the message
After running the above snippet, you should see output similar to the following: 
Created account: 0x2Ae896e791c9596c7beDeCC3E06Fa6DA9aE2B193  
Message: Hello, Coinbase Developer Platform!
Signature: 0x1b0c9cf8cd4554c6c6d9e7311e88f1be075d7f25b418a044f4bf2c0a42a93e212ad0a8b54de9e0b5f7e3812de3f2c6cc79aa8c3e1c02e7ad14b4a8f42012c2c01b
To summarize, in the example above, we:
  • Created an EVM account
  • Signed a plain text message using EIP-191 standard
  • The message was automatically prepended with the EIP-191 prefix before signing
  • Generated a cryptographic signature that can be used to verify the signer’s identity
The EIP-191 standard ensures that signed messages cannot be confused with transaction data, providing a secure way to prove ownership of an address.

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Verifying Signatures

Once you have a signature, it can be verified by anyone to confirm that the message was signed by the claimed address. This is useful for authentication systems, proving ownership, or validating off-chain agreements.
  • EIP-712 Signing: Learn about signing structured typed data with EIP-712.
  • v2 Security: Learn about the security features of v2 Server Wallet.
  • API Reference: Explore the complete API reference for EIP-191 message signing.
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