custom private key with crypto in node.js - node.js

Question

from: https://nodejs.org/api/crypto.html#crypto_class_ecdh
const alice_key = alice.generateKeys();
will generate a random private key and the corresponding public key.
But I would like to set my own private key: e8f32e723decf...
If I use :
alice.setPrivateKey("e8f32e723decf");
the object alice_key is not affected, so later:
const bob_secret = bob.computeSecret(alice_key, 'hex', 'hex');
will be wrong. Is there a way to do something like:
const alice_key = alice.generateKeys("e8f32e723decf");

Answer 1

First of all I suppose your hex string is missing a leading 0, so it should be 0e8f32e723decf.
Then it depends on your node.js version, the implementation of ECDH.setPrivateKey() changed from 5.1 to 5.2
node.js 5.0
You need to generate the keys and override them
You need to have the public and the private key
Working online example
const crypto = require('crypto');
// this is just to generate a private/public key pair
const warmup = crypto.createECDH('secp521r1');
warmup.generateKeys();
const warmup_private_key = warmup.getPrivateKey();
const warmup_public_key = warmup.getPublicKey();
// convert it to hex string to match the example
// you would store these strings somewhere I guess
private_key = warmup_private_key.toString('hex');
public_key = warmup_public_key.toString('hex');
// now let's create the ciphers
const alice = crypto.createECDH('secp521r1');
const bob = crypto.createECDH('secp521r1');
----------
// Bob gets created keys
bob.generateKeys();
// Generate Alice's keys - that's really annoying since you will override it
alice.generateKeys();
// now set the keys:
alice.setPrivateKey(private_key, "hex");
alice.setPublicKey(public_key, "hex");
// Exchange and generate the secret...
const alice_secret = alice.computeSecret(bob.getPublicKey());
const bob_secret = bob.computeSecret(alice.getPublicKey());
console.log("alice's shared secret: " + alice_secret.toString('hex') + "\n");
console.log("bob's shared secret: " + bob_secret.toString('hex') + "\n");
console.log('shared secrets match: ' + alice_secret.equals(bob_secret));
node.js >= 5.2
const crypto = require('crypto');
const alice = crypto.createECDH('secp256k1');
const bob = crypto.createECDH('secp256k1');
bob.generateKeys();
alice.setPrivateKey('0e8f32e723decf', 'hex');
const alice_secret = alice.computeSecret(bob.getPublicKey());
const bob_secret = bob.computeSecret(alice.getPublicKey());
console.log(alice_secret.equals(bob_secret));