Node.js hmac.digest() Method

The hmac.digest() method is an inbuilt application programming interface of class hmac within crypto module which is used to return the hmac hash value of inputted data.  

Syntax:

hmac.digest([encoding])

Parameter: This method takes encoding as a parameter which is an optional parameter.

Return Value: This method calculates the hmac digest of all data pass using hmac.update(). If no encoding provided then Buffer is returned, otherwise String is returned. 

Note: The hmac.digest() performs final operations. So, hmac object become unusable after calling hmac.digest(). Calling multiple hmac.digest() causing error. 

Project Setup: Create a new NodeJS project and name it hmac

mkdir hmac && cd hmac
npm init -y
npm install crypto

Now create a .js file in your project root directory and name it index.js

Example 1: 

index.js

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

// Importing crypto module
const { createHmac } = require('crypto')

// Creating and initializing algorithm
// and password
const algo = 'sha256'
const secret = 'GFG Secret Key'

// Create an HMAC instance
const hmac = createHmac(algo, secret)

// Update the internal state of
// the hmac object
hmac.update('GeeksForGeeks')

// Perform the final operations
// No encoding provided
// Return calculated hmac hash
// value as Buffer
let result = hmac.digest()

// Check whether returns value is
// instance of buffer or not
console.log(Buffer.isBuffer(result)) // true

// Convert buffer to string
result = result.toString('hex')

// Print the result
console.log(`HMAC hash: ${result}`)

Run the index.js file using the following command:

node index.js

Output:

true
HMAC hash: c8ae3e09855ae7ac3405ad60d93758edc0ccebc1cf5c529bfb5d058674695c53

Example 2:

index.js

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

// Defining myfile
const myfile = process.argv[2];

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

// Creating and initializing
// algorithm and password
const algo = 'sha256'
const secret = 'GFG Secret Key'

// Creating Hmac
const hmac = crypto.createHmac(algo, secret);

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

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

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

    if (data) {

        // Updating
        hmac.update(data);
    } else {

        // Perform the final operations
        // Encoding provided
        // Return hmac hash value
        const result = hmac.digest('base64')

        // Display result
        console.log(
    `HMAC hash value of ${myfile}: ${result}`);
    }
});

Run the index.js file using the following command:

node index.js package.json

Output:

HMAC hash value of package.json: 
L5XUUEmtxgmSRyg12gQuKu2lmTJWr8hPYe7vimS5Moc=

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