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('w3wiki') 
  
// 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

index.js

index.js

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