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Insecure encryption algorithm - Perfect Forward Secrecy

Need​

Implementation of secure encryption algorithms with Perfect Forward Secrecy

Context​

  • Usage of Java for building cross-platform applications
  • Usage of javax.crypto.Cipher for encryption and decryption operations
  • Usage of javax.crypto.spec.SecretKeySpec for generating secret keys in cryptography
  • Usage of java.security.Key for cryptographic key management

Description​

Non compliant code​

import javax.crypto.Cipher;
import javax.crypto.spec.SecretKeySpec;
import java.security.Key;

public class InsecureEncryption {
    private static final String ALGORITHM = "AES";
    private static final byte[] keyValue = new byte[]{'T', 'h', 'i', 's', 'I', 's', 'A', 'S', 'e', 'c', 'r', 'e', 't', 'K', 'e', 'y'};

    public static String encrypt(String valueToEnc) throws Exception {
        Key key = generateKey();
        Cipher c = Cipher.getInstance(ALGORITHM);
        c.init(Cipher.ENCRYPT_MODE, key);
        byte[] encValue = c.doFinal(valueToEnc.getBytes());
        return new BASE64Encoder().encode(encValue);
    }

    private static Key generateKey() throws Exception {
        Key key = new SecretKeySpec(keyValue, ALGORITHM);
        return key;
    }
}

The above code shows a simple encryption process using the Advanced Encryption Standard (AES) algorithm. Here, a static secret key is used for all encryption processes.

The method encrypt(String valueToEnc) takes a plaintext string as input and returns the encrypted string. It generates a key using the generateKey() method and initializes a cipher in the encryption mode with this key. Then, it encrypts the input string and returns the encrypted string.

The generateKey() method generates a key from a static secret key.

The vulnerability here is that the same secret key is used for all encryption processes. If this key is compromised, all messages that were encrypted with this key can be decrypted. This is a security risk because it does not provide Perfect Forward Secrecy (PFS). PFS is a property of secure communication protocols where compromise of long-term keys does not compromise past session keys. Without PFS, if the private key is compromised, it could lead to the decryption of all past and future messages encrypted with it.

Steps​

  • Replace the insecure encryption algorithm with a secure one that supports Perfect Forward Secrecy (PFS).
  • Use a strong and secure key generation algorithm to generate the encryption key.
  • Implement Perfect Forward Secrecy (PFS) by using a different encryption key for each session or communication.
  • Ensure that the encryption key is securely stored and protected.
  • Regularly rotate the encryption keys to minimize the impact of key compromise.
  • Consider using a key management system to securely manage and distribute encryption keys.

Compliant code​

import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import javax.crypto.SecretKey;
import javax.crypto.spec.IvParameterSpec;
import java.security.SecureRandom;
import java.util.Base64;

public class SecureEncryption {
    private static final String ALGORITHM = "AES/CBC/PKCS5Padding";
    private static final int KEY_SIZE = 256;
    private static final int IV_SIZE = 16;

    public static String encrypt(String valueToEnc) throws Exception {
        SecretKey key = generateKey();
        byte[] iv = generateIV();
        Cipher c = Cipher.getInstance(ALGORITHM);
        c.init(Cipher.ENCRYPT_MODE, key, new IvParameterSpec(iv));
        byte[] encValue = c.doFinal(valueToEnc.getBytes());
        return Base64.getEncoder().encodeToString(encValue);
    }

    private static SecretKey generateKey() throws Exception {
        KeyGenerator keyGen = KeyGenerator.getInstance("AES");
        keyGen.init(KEY_SIZE, new SecureRandom());
        return keyGen.generateKey();
    }

    private static byte[] generateIV() {
        byte[] iv = new byte[IV_SIZE];
        new SecureRandom().nextBytes(iv);
        return iv;
    }
}

The above code fixes the vulnerability by implementing Perfect Forward Secrecy (PFS) and using a secure encryption algorithm.

  1. The insecure AES algorithm is replaced with the secure AES/CBC/PKCS5Padding algorithm. This algorithm supports Perfect Forward Secrecy (PFS) by using a different encryption key for each session or communication.

  2. A strong and secure key generation algorithm is used to generate the encryption key. The KeyGenerator class is used to generate a secret (symmetric) key suitable for a specified algorithm. The key size is set to 256 bits, which is considered secure.

  3. An Initialization Vector (IV) is generated for each encryption operation. The IV is used in cipher block chaining (CBC) mode to ensure that identical blocks of plaintext do not result in identical blocks of ciphertext.

  4. The encryption key is securely stored and protected. The key is generated for each encryption operation and does not need to be stored.

  5. The encryption keys are regularly rotated. Since a new key is generated for each encryption operation, the keys are effectively rotated each time.

  6. The Base64 encoding is used instead of the insecure BASE64Encoder. The Base64 class provides methods for encoding and decoding binary data to or from base64.

This code ensures that even if a single key is compromised, only the data encrypted with that key is at risk. Other data, encrypted with different keys, remains secure.

References​

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