code: public static byte[] add(byte[] b1, int off1, int len1, byte[] b2, int off2, int len2) {
  		byte[] b = new byte[len1 + len2];
  		System.arraycopy(b1, off1, b, 0, len1);
  		System.arraycopy(b2, off2, b, len1, len2);
  		return b;
  	}
docs: Concatenate 2 byte arrays