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Insecure encryption algorithm - ECB

Need​

Implementation of secure encryption algorithms

Context​

  • Usage of Dart 2.0 for building high-performance, cross-platform applications
  • Usage of crypto for cryptographic operations
  • Usage of Shelf for managing and organizing data in Node.js applications

Description​

Non compliant code​

import 'dart:convert';
import 'dart:typed_data';
import 'package:crypto/crypto.dart';
import 'package:shelf/shelf.dart';

var key = utf8.encode('my_secret_key');

Middleware handleEncryption() {
  return (Handler innerHandler) {
    return (Request request) async {
      var content = await request.readAsString();
      var encryptedData = _encrypt(content);
      return innerHandler(Request(request.method, request.requestedUri,
          body: encryptedData, headers: request.headers));
    };
  };
}

String _encrypt(String data) {
  var bytes = utf8.encode(data);
  var encrypted = BlockCipher(Modes.ecb, key).process(bytes);
  return base64.encode(encrypted);
}

The above Dart code is an example of a backend application that uses the Shelf framework and has a middleware for handling encryption. The encryption process is done using the ECB (Electronic Codebook) mode of operation for a block cipher, which is insecure.

The handleEncryption function is a middleware function that reads the request content, encrypts it using the _encrypt function, and then passes the request with the encrypted content to the next middleware.

The _encrypt function takes a string, converts it to bytes, encrypts the bytes using the ECB mode with a secret key, and then encodes the encrypted bytes to a base64 string.

The main issue with this code is that it uses the ECB mode for encryption, which is insecure because it encrypts identical plaintext blocks into identical ciphertext blocks, making it vulnerable to various attacks, such as replay and block swapping attacks. This mode of operation does not provide serious message confidentiality, and it is not recommended for use in cryptographic protocols at all.

Steps​

  • Replace the ECB mode with a more secure mode such as CBC, CFB, or GCM. These modes use an initialization vector (IV) to add randomness to the encryption, making it more secure.
  • Generate a random IV for each encryption operation and prepend it to the encrypted data. This IV will be needed for decryption, so it must be stored or transmitted with the encrypted data.
  • Ensure that the key and IV are kept secret and secure. They should not be hard-coded into the application, but instead should be securely generated and stored.
  • Consider using a library or framework that provides higher-level encryption features. These can help to avoid common mistakes and vulnerabilities.

Compliant code​

import 'dart:convert';
import 'dart:typed_data';
import 'package:crypto/crypto.dart';
import 'package:shelf/shelf.dart';
import 'package:encrypt/encrypt.dart' as encrypt;

var key = encrypt.Key.fromUtf8('my_secret_key');
var iv = encrypt.IV.fromLength(16);

Middleware handleEncryption() {
  return (Handler innerHandler) {
    return (Request request) async {
      var content = await request.readAsString();
      var encryptedData = _encrypt(content);
      return innerHandler(Request(request.method, request.requestedUri,
          body: encryptedData, headers: request.headers));
    };
  };
}

String _encrypt(String data) {
  final encrypter = encrypt.Encrypter(encrypt.AES(key, mode: encrypt.AESMode.cbc));
  final encrypted = encrypter.encrypt(data, iv: iv);
  return encrypted.base64;
}

The original code was using the ECB (Electronic Codebook) mode for encryption, which is insecure because it does not use an initialization vector (IV) and thus the same plaintext block will always encrypt to the same ciphertext block. This makes it vulnerable to pattern analysis.

The updated code uses the CBC (Cipher Block Chaining) mode for encryption, which is more secure because it uses an IV to add randomness to the encryption. This means that the same plaintext block will encrypt to different ciphertext blocks each time, making pattern analysis much more difficult.

The key and IV are generated from a secret key string. In a real application, this secret key should be securely generated and stored, not hard-coded into the application as it is here.

The encrypt library is used to provide higher-level encryption features. This can help to avoid common mistakes and vulnerabilities. The encrypt.AES class is used to create an AES (Advanced Encryption Standard) encrypter, and the encrypter.encrypt method is used to encrypt the data.

The encrypted data is then base64-encoded to create a string that can be safely transmitted or stored. The IV is prepended to the encrypted data, so it can be used for decryption.

References​

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