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Node.js hmac.update() Method

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  • Last Updated : 25 May, 2021
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The hmac.update() method is an inbuilt method of class HMAC within the crypto module which is used to update the data of hmac object. 

Syntax:

hmac.update(data[, inputEncoding])

Parameters: This method takes the following two parameters:

  • data: It can be of string, Buffer, TypedArray, or DataView type. It is the data that is passed to this function.
  • inputEncoding: It is an optional parameter. It is the encoding of the data string.

Return Value: This method does not return nothing.

 

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

mkdir hmac && cd hmac
npm init -y

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.update() 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
// Return calculated hash
const result = hmac.digest('base64')
  
// Print the result
console.log(`HMAC hash: ${result}`)

Run the index.js file using the following command:

node index.js

Output:

HMAC hash: yK4+CYVa56w0Ba1g2TdY7cDM68HPXFKb+10FhnRpXFM=

Example 2:

index.js




// Node.js program to demonstrate the    
// crypto hmac.update() 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 
    // Return hash value
    const result = hmac.digest('hex')
  
    // 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: 38f0f975f8964343c24da940188eaeb6bb20842e3c5bf03ccb66773e98beeb73

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


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