Node.js crypto.createHmac() Method

Last Updated : 08 Jan, 2025

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 accepts 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.

Features

Generates a unique hash based on the content and a secret key.
Supports various cryptographic algorithms such as 'sha256', 'sha1', 'md5', etc.
Can be used with streams for processing large amounts of data.

Below examples illustrate the use of crypto.createHmac() method in Node.js:

Example 1: This example demonstrates using the crypto.createHmac() method to generate an HMAC hash of the string "GeeksforGeeks" using the SHA-256 algorithm and a secret key, then outputting the hash in hexadecimal format.

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)
					.update('GeeksforGeeks')  // updating data
                    .digest('hex');           // Encoding to be used

// Displays output
console.log(hash);

Output:

a08116905e92633e4f30eefd1276206b259305c8783642fc5b7f51c089187939

Example 2: This example demonstrates using the crypto.createHmac() method to generate an HMAC hash of the contents of the current file, read via a stream, and then outputs the hash along with the filename.

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

Summary

The crypto.createHmac() method in Node.js is a powerful tool for generating HMACs, ensuring the integrity and authenticity of data. It supports various algorithms and integrates seamlessly with other Node.js modules, making it a versatile choice for secure data handling in your applications.

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