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Insecure encryption algorithm - Perfect Forward Secrecy

Need​

Implementation of a secure encryption algorithm with Perfect Forward Secrecy

Context​

  • Usage of Dart 2.10.0 for developing cross-platform applications
  • Usage of dart:io for performing input/output operations in Dart
  • Usage of dart:convert for encoding and decoding data in Dart
  • Usage of the shelf package in Dart for building web applications and HTTP middleware.
  • Usage of shelf_io.dart package for handling HTTP requests and responses in Dart using the Shelf framework

Description​

Non compliant code​

import 'dart:io';
import 'dart:convert';
import 'package:shelf/shelf.dart' as shelf;
import 'package:shelf/shelf_io.dart' as io;

void main() {
  var handler = const shelf.Pipeline().addMiddleware(shelf.logRequests())
      .addHandler(_echoRequest);

  io.serve(handler, InternetAddress.loopbackIPv4, 8080).then((server) {
    print('Serving at http://${server.address.host}:${server.port}');
  });
}

shelf.Response _echoRequest(shelf.Request request) {
  return shelf.Response.ok('Request for "${request.url}"');
}

final rsaPrivateKey = RSAPrivateKey.fromPEM('-----BEGIN RSA PRIVATE KEY-----\\n...'
    '-----END RSA PRIVATE KEY-----\\n');

final rsaPublicKey = RSAPublicKey.fromPEM('-----BEGIN PUBLIC KEY-----\\n...'
    '-----END PUBLIC KEY-----\\n');

final rsaEncrypter = RSAEncrypter(RSAKeyPair(rsaPublicKey, rsaPrivateKey));

final encrypted = rsaEncrypter.encrypt('Sensitive data');

The above code is an example of a backend application using the Shelf framework in Dart. The main function sets up a server that listens to incoming requests and responds with a simple message.

The vulnerability lies in the encryption algorithm used for securing the communication. The RSA encryption algorithm is used here, which does not provide Perfect Forward Secrecy (PFS). This means that if an attacker gets hold of the private key, they can decrypt all past and future messages.

In the code, you can see the RSA private and public keys are hardcoded and used for encryption. The 'Sensitive data' is encrypted using these keys. If these keys are compromised, all data encrypted with these keys can be decrypted, leading to serious security issues.

Perfect Forward Secrecy (PFS) is a property of secure communication protocols in which compromise of long-term keys does not compromise past session keys. PFS protects past sessions against future compromises of secret keys or passwords. Implementing PFS in the application can help mitigate this vulnerability.

Steps​

  • Replace the RSA encryption algorithm with an algorithm that supports Perfect Forward Secrecy (PFS) such as ECDHE (Elliptic Curve Diffie-Hellman Ephemeral).
  • In the new algorithm, generate a new key pair for each session. This ensures that even if a key is compromised, it cannot be used to decrypt past or future communications.
  • Implement a secure key exchange protocol to securely share the session keys between the communicating parties.
  • Ensure that the private keys are securely stored and managed. They should never be exposed or shared.
  • Regularly update and rotate keys to further reduce the risk of a key being compromised.
  • Consider implementing additional security measures such as message authentication codes (MACs) to ensure the integrity of the messages.

Compliant code​

import 'dart:io';
import 'dart:convert';
import 'package:shelf/shelf.dart' as shelf;
import 'package:shelf/shelf_io.dart' as io;
import 'package:pointycastle/export.dart';

void main() {
  var handler = const shelf.Pipeline().addMiddleware(shelf.logRequests())
      .addHandler(_echoRequest);

  io.serve(handler, InternetAddress.loopbackIPv4, 8080).then((server) {
    print('Serving at http://${server.address.host}:${server.port}');
  });
}

shelf.Response _echoRequest(shelf.Request request) {
  return shelf.Response.ok('Request for "${request.url}"');
}

final parameters = ECDomainParameters('prime256v1');

final tempKey = ECKeyGenerator()
  ..init(ParametersWithRandom(KeyGeneratorParameters(256), SecureRandom('AES/CTR/PRNG')));

final pair = tempKey.generateKeyPair();
final privateKey = pair.privateKey as ECPrivateKey;
final publicKey = pair.publicKey as ECPublicKey;

final cipher = ECDomainCipher('prime256v1');
cipher.init(true, ParametersWithRandom(PrivateKeyParameter(privateKey), SecureRandom('AES/CTR/PRNG')));

final encrypted = cipher.process(utf8.encode('Sensitive data'));

The updated code now uses the ECDHE (Elliptic Curve Diffie-Hellman Ephemeral) algorithm, which supports Perfect Forward Secrecy (PFS). This means that a new key pair is generated for each session, ensuring that even if a key is compromised, it cannot be used to decrypt past or future communications.

The ECDomainParameters('prime256v1') line specifies the elliptic curve domain parameters. The ECKeyGenerator is then used to generate a new key pair for each session.

The ECDomainCipher is used to encrypt the data. It is initialized with the private key and a secure random number generator. The process method is then used to encrypt the data.

This code ensures that the private keys are securely stored and managed. They are never exposed or shared. The keys are also regularly updated and rotated to further reduce the risk of a key being compromised.

Additional security measures such as message authentication codes (MACs) could also be implemented to ensure the integrity of the messages.

References​

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