PolyKeyCreator.java

package com.beowulfe.hap.impl.crypto;

import org.bouncycastle.crypto.macs.Poly1305;
import org.bouncycastle.crypto.params.KeyParameter;
import org.bouncycastle.util.Pack;

class PolyKeyCreator {

	public static byte[] create(KeyParameter macKey, byte[] additionalData, byte[] ciphertext) {
		Poly1305 poly = new Poly1305();
        poly.init(macKey);
        
        if (additionalData != null) {
        	poly.update(additionalData, 0, additionalData.length);
        	if (additionalData.length % 16 != 0) {
        		int round = 16-(additionalData.length%16);
        		poly.update(new byte[round], 0, round);
        	}
        }
        
        poly.update(ciphertext, 0, ciphertext.length);
        if (ciphertext.length % 16 != 0) {
        	int round = 16-(ciphertext.length%16);
        	poly.update(new byte[round], 0, round);
        }
        
        //additional data length
        byte[] additionalDataLength;
        if (additionalData != null) {
        	additionalDataLength = Pack.longToLittleEndian(additionalData.length);
        } else {
        	additionalDataLength = new byte[8];
        }
        poly.update(additionalDataLength, 0, 8);
        byte[] ciphertextLength = Pack.longToLittleEndian(ciphertext.length);
        poly.update(ciphertextLength, 0, 8);
        
        byte[] calculatedMAC = new byte[poly.getMacSize()];
        poly.doFinal(calculatedMAC, 0);
        return calculatedMAC;
	}
}