AES 256 GCM and ECDH | Authenticated Encryption and Decryption

ecdh-aes256-gcm.mjs

/** 
 * @see https://www.youtube.com/watch?v=M7M3qeQxTq4
*/

import { createECDH, randomBytes, createCipheriv, createDecipheriv } from 'crypto';


const alice = createECDH('secp256k1');
alice.generateKeys();

const bob = createECDH('secp256k1');
bob.generateKeys();

const alicePublicKeyBase64 = alice.getPublicKey().toString('base64');
const bobPublicKeyBase64 = bob.getPublicKey().toString('base64');

const aliceSharedKey = alice.computeSecret(bobPublicKeyBase64, 'base64', 'hex');
const bobSharedKey = bob.computeSecret(alicePublicKeyBase64, 'base64', 'hex');

console.log('aliceSharedKey === bobSharedKey: ', aliceSharedKey === bobSharedKey);
console.log('Alice shared key: ', aliceSharedKey);
console.log('Bob shared key: ', bobSharedKey);

const MESSAGE = 'this is some random message...';

const IV = randomBytes(16);
const cipher = createCipheriv(
    'aes-256-gcm',
    Buffer.from(aliceSharedKey, 'hex'),
    IV
);

let encrypted = cipher.update(MESSAGE, 'utf8', 'hex');
encrypted += cipher.final('hex');

const auth_tag = cipher.getAuthTag().toString('hex');

console.table({
    IV: IV.toString('hex'),
    encrypted: encrypted,
    auth_tag: auth_tag
});

const payload = IV.toString('hex') + encrypted + auth_tag;

const payload64 = Buffer.from(payload, 'hex').toString('base64');

console.log({ payload64 });

// Bob will do from here
const bob_payload = Buffer.from(payload64, 'base64').toString('hex');

const bob_iv = bob_payload.substr(0, 32);
const bob_encrypted = bob_payload.substr(32, bob_payload.length - 32 - 32);
const bob_auth_tag = bob_payload.substr(bob_payload.length - 32, 32);

console.table({ bob_iv, bob_encrypted, bob_auth_tag });

try {
    const decipher = createDecipheriv(
        'aes-256-gcm',
        Buffer.from(bobSharedKey, 'hex'),
        Buffer.from(bob_iv, 'hex')
    );

    decipher.setAuthTag(Buffer.from(bob_auth_tag, 'hex'));

    let decrypted = decipher.update(bob_encrypted, 'hex', 'utf8');
    decrypted += decipher.final('utf8');

    console.table({ decrypted });
} catch (error) {
    console.log(error.message);
}