javax.crypto.BadPaddingException: Given final block not properly padded...tried using getbytes("UTF")

Question

I have tried adding getbytes("UTF") or getbytes("UTF-8"), since it was suggested in a similar question. It said we need to try UTF while converting bytes to string and vice a versa. But still it is not working for my code...please help

public class Password1 {

    private static final String ALGO = "AES";
    private static byte[] keyValue = new byte[]{'t','h','y','u','e','f','z','s','y','k','f','l','d','a','b','m'};

    public static void main(String[] args) {
        //Password1 p = new Password1();
        Scanner sc = new Scanner(System.in);
        String i = sc.nextLine();
        System.out.println("Password = "+i);

        try {
            String en = encrypt(i);
            System.out.println(en);
            String dec = decrypt(en);

            System.out.println("Encrypted = " + en);
            System.out.println("Decrypted = " + dec);
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    public static String encrypt(String Data) throws Exception {
        Key key = generateKey();
        Cipher c = Cipher.getInstance(ALGO);
        c.init(Cipher.ENCRYPT_MODE, key);
        byte[] encVal = c.doFinal(Data.getBytes("UTF-8"));
        String encrypted = new BASE64Encoder().encode(encVal);

        return encrypted;
    }

    public static String decrypt(String encrypted) throws Exception {
        Key key = generateKey();
        Cipher c = Cipher.getInstance(ALGO);
        c.init(Cipher.DECRYPT_MODE, key);
        //Byte bencrypted = Byte.valueOf(encrypted);
        byte[] decoded = new BASE64Decoder().decodeBuffer(encrypted);

        byte[] decValue = c.doFinal(decoded);
        String decrypted = new String(decValue);
        return decrypted;
    }

    private static Key generateKey() throws Exception {
        MessageDigest sha = MessageDigest.getInstance("SHA-1");
        keyValue = sha.digest(keyValue);
        keyValue = Arrays.copyOf(keyValue, 16);
        SecretKeySpec key = new SecretKeySpec(keyValue, ALGO);
        return key;
    }

}

Answer 1

When you call encrypt() you replace the password by its hash, and then use the hash as a key.

Then you call decrypt(), and rehash the hash, and use the hashed hash as the key. So you're not using the same key for encryption and decryption.

Generate the key once in main(), and pass it as parameter to encrypt() and decrypt(). Make keyValue final. Or even better, make it a local variable of main.