Node.js ecdh.setPrivateKey() Method

The ecdh.getPrivateKey() method is an inbuilt application programming interface of class ECDH within the crypto module which is used to set the private key of the Elliptic Curve Diffie-Hellman (ECDH) object. The encoding of the key can be specified using the encoding parameter.

An error would be thrown if the private key is not valid for the specified curve. The setting of the private key using this method will automatically generate and set the corresponding public key in the ECDH object.

Syntax:

ecdh.setPrivateKey( privateKey, encoding )

Parameters: This method accepts two parameters as mentioned above and described below:

• privateKey: This is the private key that needs to be set. It can be given in the format of a string, ArrayBuffer, Buffer, TypedArray, or DataView.
• encoding: In encoding string value that specifies the encoding of the returned value. It is an optional parameter.

Return Value: It returns the Elliptic Curve DiffieHellman public key in the specified encoding. When the encoding is not provided, it is returned as a Buffer, otherwise, a String is returned.

The examples below demonstrate this method:

Example 1:

Javascript

const crypto = require('crypto');

// Generate an ECDH object for geekA
const geekA = crypto.createECDH('secp521r1');

// Generate an ECDH object for geekB
const geekB = crypto.createECDH('secp521r1');

// Create a private key of geekA
geekA.setPrivateKey("thisisasecretkey!");

// Create a private key of geekB
geekB.setPrivateKey("thisisanotherkey!");

// Get the private keys of both the geeks
let geekAPrivateKey = geekA.getPrivateKey();
let geekBPrivateKey = geekB.getPrivateKey();

console.log("Private Key of Geek A is:",
  geekAPrivateKey);
console.log("Private Key of Geek B is:",
  geekBPrivateKey);

Output:

Private Key of Geek A is: <Buffer 74 68 69 73 69 73 61 73 65 63 72 65 74 6b 65 79 21>
Private Key of Geek B is: <Buffer 74 68 69 73 69 73 61 6e 6f 74 68 65 72 6b 65 79 21>

Example 2:

Javascript

const crypto = require('crypto');

// Generate an ECDH object for geekA
const geekA = crypto.createECDH('secp521r1');

// Generate an ECDH object for geekB
const geekB = crypto.createECDH('secp521r1');

// Create a private key of geekA
// with "hello" in hex format
geekA.setPrivateKey("68656c6c6f", "hex");

// Create a private key of geekB
// with "world" in base64 format
geekB.setPrivateKey("d29ybGQ=", "base64");

// Get the private keys of both the geeks
// in 'utf-8' encoding
let geekAPrivateKey =
  geekA.getPrivateKey('utf-8');
let geekBPrivateKey =
  geekB.getPrivateKey('utf-8');

console.log("Private Key of Geek A is:",
  geekAPrivateKey);
console.log("Private Key of Geek B is:",
  geekBPrivateKey);

Output:

Private Key of Geek A is: hello
Private Key of Geek B is: world

Reference: https://nodejs.org/api/crypto.html#crypto_ecdh_setprivatekey_privatekey_encoding