How to Resolve a BadPaddingException in Java's doFinal Method?

What causes BadPaddingException errors in Java's doFinal method, and how can they be resolved?

try {
    Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
    cipher.init(Cipher.DECRYPT_MODE, secretKey, ivParameterSpec);
    byte[] decryptedText = cipher.doFinal(encryptedText);
} catch (BadPaddingException e) {
    System.err.println("Bad padding exception: " + e.getMessage());
}

The BadPaddingException in Java typically arises during cryptographic operations when the padding of input data is incorrect. This often occurs in decryption processes using Cipher's doFinal method.

// Example of proper initialization and decryption:
Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
cipher.init(Cipher.DECRYPT_MODE, secretKey, iv);
// Make sure to use the correct encrypted data
byte[] decryptedData = cipher.doFinal(encryptedData);

Causes

• Incorrect key or initialization vector (IV) used for decryption.
• Data may have been tampered with or corrupted before decryption.
• The padding scheme used for encryption does not match the one expected in decryption.
• Using the wrong mode of operation or Cipher configuration.

Solutions

• Verify that the same key and IV are being used for encryption and decryption.
• Ensure data integrity and check if the encrypted data has been modified after encryption.
• Match the padding scheme across both encryption and decryption processes; for example, both should use PKCS5Padding.
• Check that the cipher instance used for decryption matches the configuration used for encryption.

Mistake: Using different keys for encryption and decryption.

Solution: Always use the same secret key for both operations.

Mistake: Incorrectly setting up the IV or not using it at all.

Solution: Ensure the IV is properly initialized and used consistently.

Mistake: Not validating the integrity of encrypted data.

Solution: Implement checks to verify data has not been altered before decryption.