encryption/decryption using AES/ECB/NoPadding

Question

Following are my encrypt/decrypt methods:

private String decrypt_data(String encData) 
                throws NoSuchAlgorithmException, NoSuchPaddingException, InvalidKeyException, IllegalBlockSizeException, BadPaddingException
    {
        String key = "bad8deadcafef00d";
        SecretKeySpec skeySpec = new SecretKeySpec(key.getBytes(), "AES");
        Cipher cipher = Cipher.getInstance("AES/ECB/NoPadding");

        cipher.init(Cipher.DECRYPT_MODE, skeySpec);

        System.out.println("Base64 decoded: "+Base64.decode(encData.getBytes()).length);
        byte[] original = cipher.doFinal(Base64.decode(encData.getBytes()));
        return new String(original).trim();     
    }

    private String encrypt_data(String data) 
                throws NoSuchAlgorithmException, NoSuchPaddingException, InvalidKeyException, IllegalBlockSizeException, BadPaddingException
    {
        String key = "bad8deadcafef00d";
        SecretKeySpec skeySpec = new SecretKeySpec(key.getBytes(), "AES");
        Cipher cipher = Cipher.getInstance("AES/ECB/NoPadding");

        cipher.init(Cipher.ENCRYPT_MODE, skeySpec);

        System.out.println("Base64 encoded: "+ Base64.encode(data.getBytes()).length);

        byte[] original = cipher.doFinal(Base64.encode(data.getBytes()));
        return new String(original);
    }

So now when I am trying to encrypt, I am getting this exception:

javax.crypto.IllegalBlockSizeException: Input length not multiple of 16 bytes
    at com.sun.crypto.provider.CipherCore.finalNoPadding(CipherCore.java:854)
    at com.sun.crypto.provider.CipherCore.doFinal(CipherCore.java:828)
    at com.sun.crypto.provider.CipherCore.doFinal(CipherCore.java:676)
    at com.sun.crypto.provider.AESCipher.engineDoFinal(AESCipher.java:313)
    at javax.crypto.Cipher.doFinal(Cipher.java:2087)

I have tried with cipher instance AES/ECB/PKCS5Padding in both encrypt and decrpt. It works only for encryption and not for decryption. I suppose padding is needed as data size is not multiple of 16bytes. 'data' byte length was printed as 152 so tried appending eight \0 characters to data and then encrypt, it didn't work either.

Answer 1

I saw another mistake in your code :

Even if your encyption method get working, you're decryption method is not going to work. Indeed you are encrypting using Base64 followed bye AES. And you decrypt the whole thing using Base64 followed by AES.

I am almost sure that this two type of encryption are not exchangeables. (you must decrypt AES then Base64).

Considering this answer : javax.crypto.IllegalBlockSizeException : Input length must be multiple of 16 when decrypting with padded cipher , without the use of padding (NoPadding arg), you have to use an input String with a length multiple of 16.

If we correct your code with my remark and if we let the cipher manage the padding, we get the following code, which works well :

private static String decrypt_data(String encData)
        throws NoSuchAlgorithmException, NoSuchPaddingException,
        InvalidKeyException, IllegalBlockSizeException, BadPaddingException {
    String key = "bad8deadcafef00d";
    SecretKeySpec skeySpec = new SecretKeySpec(key.getBytes(), "AES");
    Cipher cipher = Cipher.getInstance("AES");

    cipher.init(Cipher.DECRYPT_MODE, skeySpec);

    System.out.println("Base64 decoded: "
            + Base64.decode(encData.getBytes()).length);
    byte[] original = cipher
            .doFinal(Base64.decode(encData.getBytes()));
    return new String(original).trim();
}

private static String encrypt_data(String data)
        throws Exception {
    String key = "bad8deadcafef00d";
    SecretKeySpec skeySpec = new SecretKeySpec(key.getBytes(), "AES");
    Cipher cipher = Cipher.getInstance("AES");

    cipher.init(Cipher.ENCRYPT_MODE, skeySpec);

    System.out.println("Base64 encoded: "
            + Base64.encode(data.getBytes()).length);

    byte[] original = Base64.encode(cipher.doFinal(data.getBytes()));
    return new String(original);
}

Answer 2

To address your specific problem, I think you just need to add the 8 bytes padding like you tried, but use something that is valid in a java string (like spaces) instead.