Shamir's secret sharing using node.js

index.js

const crypto = require('crypto');
// All by chatgpt4 except this shim line below
global.window = {};
const secrets = require('secrets.js');

// Function to generate RSA key pair
function generateKeyPair() {
    return crypto.generateKeyPairSync('rsa', {
        modulusLength: 2048,
        publicKeyEncoding: { type: 'spki', format: 'pem' },
        privateKeyEncoding: { type: 'pkcs8', format: 'pem' }
    });
}

// Function to split the private key using Shamir's Secret Sharing
function splitPrivateKey(privateKey, totalShares, threshold) {
    // Convert the private key to a hex string
    const hexPrivateKey = Buffer.from(privateKey).toString('hex');

    // Generate the shares
    return secrets.share(hexPrivateKey, totalShares, threshold);
}

// Function to reconstruct the private key from shares
function reconstructPrivateKey(shares) {
    const combinedHex = secrets.combine(shares);
    return Buffer.from(combinedHex, 'hex').toString();
}

// Main function to demonstrate the process
function main() {
    const totalShares = 5;   // Total number of shares to split the private key into
    const threshold = 3;     // Minimum number of shares required to reconstruct the key

    // Generate RSA key pair
    const { publicKey, privateKey } = generateKeyPair();

    // Split the private key into shares
    const shares = splitPrivateKey(privateKey, totalShares, threshold);

    // Display the public key and shares
    console.log('Public Key:', publicKey);
    shares.forEach((share, index) => console.log(`Share ${index + 1}:`, share));

    // Example of reconstructing the private key (using the first 'threshold' shares)
    const reconstructedPrivateKey = reconstructPrivateKey(shares.slice(0, threshold));
    console.log('Reconstructed Private Key:', reconstructedPrivateKey);
}

main();