AES encryption with NoPadding in blackberry

Question

I am new to blackberry development and got to complete a task of encryption and decryption with AES/ECB/NoPadding. I used below code, from internet.

Encryption method:

public static byte[] encrypt( byte[] keyData,String message )
    throws Exception
{


        byte[] data = message.getBytes("UTF-8");

        // Create the AES key to use for encrypting the data.
        // This will create an AES key using as much of the keyData
        // as possible.


        if ((data.length % 16) != 0 ) {
            StringBuffer buffer = new StringBuffer(message);
            int moduleOut = data.length % 16;
            int padding =  16 - moduleOut;
            for(int i = 0 ; i < padding; i++){
                buffer.append(" ");
            }
            data = buffer.toString().getBytes("UTF-8");
        }

        AESKey key = new AESKey( keyData);

        NoCopyByteArrayOutputStream out = new NoCopyByteArrayOutputStream(data.length);
        AESEncryptorEngine engine = new AESEncryptorEngine(key);
        BlockEncryptor encryptor = new BlockEncryptor(engine, out);


        encryptor.write(data,0,data.length);
        int finalLength = out.size();
        byte[] cbytes = new byte[finalLength];
        System.arraycopy(out.toByteArray(), 0, cbytes, 0, finalLength);
//      encryptor.close();
//      out.close();
        return cbytes;

    }

Decryption method:

    public static byte[] decrypt(byte[] keyData, byte[] base64EncodedData)
    throws CryptoException, IOException 
    {

//      String base64EncodedData=new String(base64EncodedData);

        byte[] cipherText =Base64ToBytes(new String(base64EncodedData));
        // First, create the AESKey again.
        AESKey key = new AESKey(keyData);

        // Now, create the decryptor engine.
        AESDecryptorEngine engine = new AESDecryptorEngine(key);

        // Create the BlockDecryptor to hide the decryption details away.
        ByteArrayInputStream input = new ByteArrayInputStream(cipherText);
        BlockDecryptor decryptor = new BlockDecryptor(engine, input);

        // Now, read in the data.
        byte[] temp = new byte[100];
        DataBuffer buffer = new DataBuffer();

        for (;;) 
        {
            int bytesRead = decryptor.read(temp);
            buffer.write(temp, 0, bytesRead);

            if (bytesRead < 100) 
            {
                // We ran out of data.
                break;
            }
        }

        byte[] plaintext = buffer.getArray();       
        return plaintext;

        }

Base64 to Bytes convert method:

private static byte[] Base64ToBytes(String code) {

        byte[] aesString = null;
        try 
        {
            aesString = Base64InputStream.decode(code);
        }
        catch (IOException ioe)
        {
        }
        return aesString;
    }

Now the problem is when i encrypt my string with above method i get padded unicodes at the end of the string, which is not tolerable at Server side.

I know it is due to PKCS5FormatterEngine and its normal to have characters appended at end of the string while using this class.

But what if i want to encrypt and decrypt string with AES/ECB method and that too with NoPadding. I know ECB is not a secure mode and all that but server is with PHP and ready, works great in Android, and J2ME.

Please guide. How to bypass PKCS5FormatterEngine or encrypt without any padding.

Update:

I tried to use Cipher class in Blackberry as i used in Android and J2ME but it seems unavailable in net_rim_api.jar, even i tried downloading bouncy castle jar file and dependent class NoSuchAlogrithmException so java.security jar (org.osgi.foundation-1.0.0.jar), compiles but when i try to run it stops saying duplicate classes found. It has a problem with few duplicate classes in jar i have kept for java.security.

If you have solution towards this, please let me know.

Update for Answer: I have update my code with full encryption and decryption code and also check the answer for better understanding.

Answer 1

Not sure this is really an answer in general, but it might help in this specific case, so I am adding it as such.

You can't really use AES without some padding, because the AES processing does not wish to assume the data you supply will be a multiple of 16 bytes. However if you actually always supply a buffer that is a multiple of 16 bytes, then you can just encrypt your data with code like this:

        AESEncryptorEngine engine = new AESEncryptorEngine( key );
        for ( int j = 0; j < ciphertext.length - 15;  ) {
            engine.encrypt(plainText, j, ciphertext, j);
            j = j+16;
        }

So how do you make sure this works OK at the other end? It may or may not be possible to do this - it actually depends on what is being transferred.

But if, for example, you were passing XML data, then you can append spaces to make the data up to a 16 byte boundary and these will be decrypted as spaces by the Server, and then ignored by the parsing. You can add redundant padding bytes to a variety of file formats and the padding will be ignored, it all depends on the file format being processed.

Update

Given that the actual data is JSON and that I believe that JSON will ignore trailing spaces, the approach I would take is append spaces to the JSON data before encrypting it.

So convert the JSON string to bytes:

byte [] jsonBytes = jsonString.getBytes("UTF-8");

pad this if you need too:

if ( (jsonBytes.length % 16) != 0 ) {
// Now pad this with spaces
}

and you can encrypt the result with no worries about padding bytes.