Recently I learned how to generate shared secrets using ECDH in Node.JS, but I still had to know how to use this shared secret. Here is one application for it. Use the ECDH to generate a shared secret and then use that shared secret to cipher/decipher messages between both parties, in this case Joe and Zoe. Here is the code:

console.log("\n- ---[ Elliptic Curve Diffie-Hellman and AES Example ]--- -");
console.log("\n");

var crypto = require('crypto');
var assert = require('assert');

var CURVE_ALGORTHM = 'wap-wsg-idm-ecid-wtls11';

console.log("Elliptic Curve Algorithm: " + CURVE_ALGORTHM);
console.log("\n");

// Generate Zoe's keys...
var zoe = crypto.createECDH(CURVE_ALGORTHM);
var zoeKey = zoe.generateKeys();

// Generating Joe's keys...
var joe = crypto.createECDH(CURVE_ALGORTHM);
var joeKey = joe.generateKeys();

// Exchange and generate secret...
var zoeSecret = zoe.computeSecret(joeKey);
var joeSecret = joe.computeSecret(zoeKey);

assert.strictEqual(zoeSecret.toString('hex'), joeSecret.toString('hex'));

console.log("Zoe's Public Key: " + zoe.getPublicKey('hex'));
console.log("Zoe's Private Key: " + zoe.getPrivateKey('hex'));

console.log("\n");

console.log("Joe's Public Key: " + joe.getPublicKey('hex'));
console.log("Joe's Private Key: " + joe.getPrivateKey('hex'));

console.log("\n");

zoeSecret = zoeSecret.toString('hex');
joeSecret = joeSecret.toString('hex');

console.log('Zoe secret: ' + zoeSecret);
console.log('Joe secret: ' + joeSecret);

console.log("\n");

// Using the generated shared Secrets to cipher/decipher messages between Zoe and Joe
var AES256 = "aes256";

var zoeCipher = crypto.createCipher(AES256, zoeSecret);
var zoeDecipher = crypto.createDecipher(AES256, zoeSecret);

var joeCipher = crypto.createCipher(AES256, joeSecret);
var joeDecipher = crypto.createDecipher(AES256, joeSecret);

// Zoe ciphers a message for Joe
var msg1 = "Hey Joe, I'm Zoe";
var eMsg1 = zoeCipher.update(msg1, 'utf8', 'hex');
eMsg1 += zoeCipher.final('hex');
console.log("Zoe says (clear): " + msg1);
console.log("Zoe says (ciphered): " + eMsg1);

console.log('\n');

// Joe deciphers Zoe's message
var dMsg1 = joeDecipher.update(eMsg1, 'hex', 'utf8');
dMsg1 += joeDecipher.final('utf8');
console.log("Joe receives (ciphered): " + eMsg1);
console.log("Joe receives (deciphered): " + dMsg1);

console.log('\n');

// Joe ciphers a message for Zoe
var msg2 = "Hey Zoe, how are you doing?";
var eMsg2 = joeCipher.update(msg2, 'utf8', 'hex');
eMsg2 += joeCipher.final('hex');
console.log("Joe says (clear): " + msg2);
console.log("Joe says (ciphered): " + eMsg2);

console.log('\n');

// Zoe deciphers Joe's message
var dMsg2 = zoeDecipher.update(eMsg2, 'hex', 'utf8');
dMsg2 += zoeDecipher.final('utf8');
console.log("Zoe receives (ciphered): " + eMsg2);
console.log("Zoe receives (deciphered): " + dMsg2);

Your console output should be similar to this:

E:\NodeJS>node ecdh-aes.js

- ---[ Elliptic Curve Diffie-Hellman and AES Example ]--- -


Elliptic Curve Algorithm: wap-wsg-idm-ecid-wtls11


Zoe's Public Key: 040070230a08f8fc62bf2f10430a5a2af6b7c56c931fc191d97e21c72ee32301da452a99347fc1bb13db4ee4f890ca4539025dfa153b2b0086aa4d5e16
Zoe's Private Key: 2b2d30cd93f9a6a20b2ec6c5ef15462e69001c6d56cd600457f47ade70


Joe's Public Key: 0400facfc4a4a2116444aa8f75b3afbf861aa85f4b451f999da94e6ba23b1a008ab778a77578a81cf54760320d0813bf0a855324014fe89501d0273249
Joe's Private Key: 3285f8be0f9c18b65de80aae0103c7d9811ef32decff46f9bfc0925d25


Zoe secret: 01b874f549145a04e6cd75fae7bf22c64a664960b5f0ecd9ddf061de767f
Joe secret: 01b874f549145a04e6cd75fae7bf22c64a664960b5f0ecd9ddf061de767f


Zoe says (clear): Hey Joe, I'm Zoe
Zoe says (ciphered): 5bb662241f3a0b443e11b7162561a059e8a8a6f206569db8d12400a3e7bbb1ef


Joe receives (ciphered): 5bb662241f3a0b443e11b7162561a059e8a8a6f206569db8d12400a3e7bbb1ef
Joe receives (deciphered): Hey Joe, I'm Zoe


Joe says (clear): Hey Zoe, how are you doing?
Joe says (ciphered): c4b53b00b5e93170bb777b4036d377fea509b0c214df9459a5544e22aeb0b18e


Zoe receives (ciphered): c4b53b00b5e93170bb777b4036d377fea509b0c214df9459a5544e22aeb0b18e
Zoe receives (deciphered): Hey Zoe, how are you doing?