Node.js crypto.createHmac() Method

The crypto.createHmac() method is used to create an Hmac object that uses the stated ‘algorithm’ and ‘key’. Syntax:

crypto.createHmac( algorithm, key, options )

Parameters: This method accept three parameters as mentioned above and described below:

• algorithm: It is dependent on the accessible algorithms which are favored by the version of OpenSSL on the platform. It returns string. The examples are sha256, sha512, etc.
• key: It is the HMAC key which is used to create the cryptographic HMAC hash. It returns string, Buffer, TypedArray, DataView, or KeyObject. And if it is a KeyObject, then its type must be secret.
• options: It is optional parameter and used to control stream behavior. It returns an object.

Return Type: It returns Hmac object. Below examples illustrate the use of crypto.createHmac() method in Node.js: Example 1:

javascript

// Node.js program to demonstrate the
// crypto.createHmac() method

// Includes crypto module
const crypto = require('crypto');

// Defining key
const secret = 'GfG';

// Calling createHmac method
const hash = crypto.createHmac('sha256', secret)

                   // updating data
                   .update('GeeksforGeeks')

                   // Encoding to be used
                   .digest('hex');

// Displays output
console.log(hash);

Output:

a08116905e92633e4f30eefd1276206b259305c8783642fc5b7f51c089187939

Example 2:

javascript

// Node.js program to demonstrate the
// crypto.createHmac() method

// Defining myfile
const myfile = process.argv[1];

// Includes crypto and  fs module
const crypto = require('crypto');
const fs = require('fs');

// Creating Hmac
const creathmac = crypto.createHmac('sha1', 'CS-Portal!');

// Creating read stream
const readfile = fs.createReadStream(myfile);

readfile.on('readable', () => {

 // Calling read method to read data
  const data = readfile.read();
  if (data)

    // Updating
    creathmac.update(data);
  else
   {
    // Encoding and displaying filename
    console.log("The hmac object returns:",
    `${creathmac.digest('hex')} ${myfile}`);
  }
});
console.log("Program done!");
console.log();

Output:

Program done!
The hmac object returns: 4605d44703c2620fc2574c9a9216bd3267457324 /run_dir/interp.js

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