Here is an article about Metamask integration with Ethers for signed typed data:
KMS Integration with Ethers: A Step-by-Step Guide to Signed Typed Data
In recent years, the use of Key Management Systems (KMS) has become increasingly popular in blockchain development. One such system is Amazon KMS (Amazon Web Services Key Management Service), which provides secure key management and encryption services for various applications.
A common requirement in developing smart contracts on Ethereum is the ability to sign typed data using a private key stored in an environment variable. In this article, we will explore how to integrate KMS with Ethers to achieve verification of signed typed data.
Why Sign Typed Data?
Before diving into the integration process, let’s briefly discuss why signed typed data (EIP712) is essential:
- Tamper-proof
: The signature provides proof that the data was created and signed by the holder.
- Non-repudiation: Ensures that the sender cannot deny that they created the data.
Environment variables for private keys
To store private keys securely, you should use environment variables. This approach allows users to manage their keys without exposing them in code.
// Setting environment variable
const privateKey = process.env.KEY_PRIVATE;
Setting up KMS with Ethers
To integrate Metamask with Ethers, we will use the ethers and ethers.js packages. First, install the required packages:
npm install ethers @types/ethers
Next, set up your Ethereum wallet and account. For this example, let’s assume you have a MetaMask wallet.
Generating Signed Typed Data
We will use the ethers/web3 package to generate signed typed data via KMS. First, create a contract with a function that generates signed typed data:
// Example of EIP-712 struct definition for typed data
const Struct = {
fields: [
{ name: 'name', type: 'string' },
{ name: 'version', type: 'number' }
]
};
export const typedDataStruct = Struct;
export function generateSignedTypedData(data) {
// Generate a random signature
const sig = crypto.createSign('SHA256');
sig.update(Buffer.from(typedDataStruct, 'utf8'));
// Sign data using private key (environment variable)
const signature = sig.sign(privateKey);
return { signature };
}
Signing Typed Data with Metamask
Now that we have a generateSignedTypedData function, let’s integrate it with your contract. First, create an interface for signed typed data:
// EIP-721 structure definition for the example contract
const Struct = {
fields: [
{ name: 'name', type: 'string' },
{ name: 'version', type: 'number' }
]
};
export const EIP721 = Struct;
export function generateSignedTypedData(data) {
return generateSignedTypedData({ name: data.name, version: data.version });
}
Finally, we can use the EIP721 interface to sign the typed data in our contract:
// Example contract code snippet (Node.js)
import { EIP721 } from './interface';
const contract = new ethers.Contract('0x... contract address...', EIP721);
async function function1() {
const data = { name: 'Example Contract', version: 1 };
try {
const signature = await contract.generateSignedTypedData(data);
console.log(Signature: ${signature});
} catch (error) {
console.error(error);
}
}
Running the Code
To run this code, you will need to set up a local Ethereum blockchain using MetaMask or another compatible wallet. Once you have a valid account and a private key set up, you can compile your EIP-721 contract and use it with Metamask.
“`bash
hardhat development npx.