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 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.

// 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.

// 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