Here is an article about integrating Metamask with Ethers signed data:

KMS Integration with Ethers: A Step-by-Step Guide to Signed Data

The use of key management systems (KMS) in blockchain development has become increasingly popular in recent years. One such system is Amazon KMS (Amazon Web Services Key Management Service), which provides secure key management and encryption services for a variety of applications.

One common requirement when developing smart contracts on Ethereum is the ability to sign the data being written 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 data being written.

Why Sign Data?

Before we delve into the integration process, let’s briefly discuss why signed data (EIP712) is important:

• Unambiguous: A signature proves 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

Environment variables should be used to securely store private keys. This approach allows users to manage their keys without exposing them in code.

// Setting the 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 ether @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 using KMS. First, create a contract with a function that generates signed typed data:

// Example of EIP-712 structure definition for typed data
const Struct = {
fields: [
{name: 'name', type: 'string'},
{name: 'version', type: 'number'}
]
};
export const typedDataStruct = Structure;
export function generSignedTypedData(data) {
// Generate a random signature
const sig = crypto.createSign('SHA256');
sig.update(Buffer.from(typedDataStruct, 'utf8'));
// Signing data using a private key (environment variable)
const signature = sig.sign(privateKey);
return {signature};
}

Signing typed data using metamask

Now that we have the function "generateSignedTypedData", let's integrate it with your contract. First, create an interface for signed typed data:

// EIP-721 structure definition for a sample contract
const Struct = {
fields: [
{name: 'name', type: 'string'},
{name: 'version', type: 'number'}
]
};
export const EIP721 = Structure;
export function generateSignedTypedData(data) {
return generateSignedTypedData({name: data.name, version: data.version});
}

Finally, we can use the "EIP721" interface to sign the recorded 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: 'Sample 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 private key setup, you can compile your EIP-721 contract and use it with Metamask.

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