How to Fix javax.crypto.BadPaddingException: Given Final Block Not Properly Padded in Java Encryption?

What causes the javax.crypto.BadPaddingException in my password-based encryption implementation?

javax.crypto.BadPaddingException: Given final block not properly padded

The javax.crypto.BadPaddingException: Given final block not properly padded error is common when working with Java's cryptographic libraries, particularly when dealing with block ciphers like DES. This issue typically arises due to incorrect padding or an improperly sized input buffer during encryption or decryption.

public byte[] encrypt(byte[] array) throws CrypterException {
    try {
        // Check if padding is necessary
        int blockSize = cipher.getBlockSize();
        int paddedLength = (array.length + blockSize - 1) / blockSize * blockSize; // Align to block size
        byte[] paddedArray = Arrays.copyOf(array, paddedLength);

        Cipher cipher = Cipher.getInstance("DES/ECB/PKCS5Padding");
        cipher.init(Cipher.ENCRYPT_MODE, key);

        return cipher.doFinal(paddedArray);
    } catch (Exception e) {
        e.printStackTrace();
    }
    return null;
}

Causes

• The input data length is not a multiple of the block size (8 bytes for DES).
• Mismatch between encryption and decryption modes (e.g., using different keys).
• Incorrect initialization vector (IV) or mode of operation used in encryption/decryption.
• Not using the same padding scheme for both encryption and decryption.

Solutions

• Ensure the input data length is aligned with the block size by padding it manually if necessary.
• Verify that the same key is used for both encryption and decryption processes.
• Make sure that the encryption algorithm's parameters such as padding and mode are consistently applied.
• Check if you're reusing the same Cipher instance for different operations; always create a new instance.

Mistake: Using the same `Cipher` instance for multiple encryption or decryption operations.

Solution: Create a new `Cipher` instance for each encrypt or decrypt call.

Mistake: Not padding the input data correctly before encryption when its size is not a multiple of the block size.

Solution: Use a padding scheme or ensure that the data is padded to the correct length.

Mistake: Mixing up encryption and decryption modes or keys.

Solution: Always verify that the same key and parameters are used across both methods.