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Insecure generation of random numbers - Static IV

Need​

Secure generation of random numbers and dynamic initialization vectors

Context​

  • Usage of Node.js v14.0.0 for server-side JavaScript development
  • Usage of Express for building web applications and APIs
  • Usage of crypto for cryptographic operations and secure data handling

Description​

Non compliant code​

import express from 'express';
import crypto from 'crypto';

const app = express();

// Insecure generation of static IV
const staticIV = Buffer.from('0123456789abcdef', 'hex');

app.get('/', (req, res) => {
  // Generate a random number using the static IV
  const cipher = crypto.createCipheriv('aes-256-cbc', 'mySecretKey', staticIV);
  const encryptedData = cipher.update('Sensitive data', 'utf8', 'hex') + cipher.final('hex');

  res.send(encryptedData);
});

app.listen(3000, () => {
  console.log('Server is running on port 3000');
});

The vulnerability in this code is the insecure generation of random numbers, specifically the use of a static, hardcoded value for the initialization vector (IV).

In the code, a static IV is defined as a Buffer object with the value '0123456789abcdef' in hexadecimal format. This IV is then used in the creation of a cipher object using the 'aes-256-cbc' algorithm and a static secret key. The cipher object is used to encrypt the string 'Sensitive data' and send the encrypted data as a response.

The problem with using a static IV is that it allows an attacker to perform a reverse engineering attack. By knowing the initialization vector, an attacker can analyze the encrypted data and potentially predict the random values that should remain as secrets. This knowledge can then be used to craft new attack vectors.

To mitigate this vulnerability, it is recommended to generate initialization vectors randomly using mechanisms with secure randomness and high entropy. This ensures that the IVs are unpredictable and cannot be easily reverse engineered by an attacker.

Steps​

  • Replace the static IV with a randomly generated IV
  • Use a secure random number generator to generate the IV
  • Ensure the IV has high entropy
  • Update the code to use the randomly generated IV in the cipher
  • Remove the static IV from the code

Compliant code​

import express from 'express';
import crypto from 'crypto';

const app = express();

app.get('/', (req, res) => {
  // Generate a random IV
  const iv = crypto.randomBytes(16);

  // Generate a random number using the random IV
  const cipher = crypto.createCipheriv('aes-256-cbc', 'mySecretKey', iv);
  const encryptedData = cipher.update('Sensitive data', 'utf8', 'hex') + cipher.final('hex');

  res.send(encryptedData);
});

app.listen(3000, () => {
  console.log('Server is running on port 3000');
});

The fixed code addresses the vulnerability by generating random initialization vectors (IV) using a secure mechanism. Here's how the code achieves this:

  1. The code imports the necessary modules, express and crypto, to create a web server and perform cryptographic operations.

  2. The code creates an instance of the Express application by calling express() and assigns it to the app variable.

  3. The code defines a route for the root URL ("/") using app.get(). This route handles incoming GET requests.

  4. Inside the route handler function, the code generates a random IV using the crypto.randomBytes() function. The crypto module provides cryptographic functionality, and randomBytes() generates random data of the specified length.

  5. The code then creates a cipher object using crypto.createCipheriv(). It uses the AES-256-CBC encryption algorithm and the 'mySecretKey' as the encryption key. The IV generated in the previous step is passed as the initialization vector to the cipher.

  6. The code encrypts the string 'Sensitive data' using the cipher object. It calls cipher.update() with the input data, encoding type ('utf8'), and output format ('hex'). The result is concatenated with the output of cipher.final('hex') to get the encrypted data.

  7. Finally, the code sends the encrypted data as the response to the client using res.send().

  8. The code starts the server by calling app.listen() and specifying the port number (3000). A log message is printed to the console to indicate that the server is running.

By generating a random IV using crypto.randomBytes(), the code ensures that each encryption operation uses a unique and unpredictable IV. This prevents attackers from predicting the random values and crafting new attack vectors.

References​

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