MessageEncryption.java

package protocol;

import java.nio.ByteBuffer;
import java.nio.ByteOrder;

public class MessageEncryption {
	
	public byte[] encrypt(byte[] data, int crcSeed) { return encryptWithCRC(data, crcSeed, true); }
	public byte[] decrypt(byte[] data, int crcSeed) { return encryptWithCRC(data, crcSeed, false); }
	private byte[] encryptWithCRC(byte[] data, int crcSeed, boolean out) {

		int startingIndex = 2;
		
		if (data.length < 4)
			return new byte[] { };
		
		if (data[0] > 0x00 && data[0] < 0x10)
			startingIndex = 1;
		
		ByteBuffer sourceByteBuffer = ByteBuffer.wrap(data).order(ByteOrder.LITTLE_ENDIAN);
		ByteBuffer resultByteBuffer = ByteBuffer.allocate(data.length).order(ByteOrder.LITTLE_ENDIAN);

		try {
			resultByteBuffer.put(data[0]);
			if (startingIndex > 1)
				resultByteBuffer.put(data[1]);
			
			if (data.length < 6)
				for (int i = startingIndex; i < data.length; i++)
					resultByteBuffer.put((byte)(data[i] ^ crcSeed));
			else {
				
				resultByteBuffer.putInt(sourceByteBuffer.getInt(startingIndex) ^ crcSeed);
				
				int i = startingIndex + 4;
				
		        for (int j = startingIndex; i <= data.length - 4; i += 4, j += 4)
		        	resultByteBuffer.putInt(sourceByteBuffer.getInt(i) ^ (out ? resultByteBuffer.getInt(j) : sourceByteBuffer.getInt(j)));
		    	for (int j = i - 4; i < data.length; i++)
		    		resultByteBuffer.put((byte) (data[i] ^ (out ? resultByteBuffer.get(j) : sourceByteBuffer.get(j))));
		    	
			}
			
	        return resultByteBuffer.array();
	        
		} catch (java.lang.ArrayIndexOutOfBoundsException e) {
			
			return new byte[] { };
		
		} catch (java.lang.IndexOutOfBoundsException e) {
		
			return new byte[] { };
		
		}
		
	}
	
}