hexToByte

  private byte [] hexToByte(String hexStr)
  throws NumberFormatException {
    byte bArray[] = null;
    try {
      if (hexStr.length() < 2)
        throw new NumberFormatException(" Not long enough." +
            "At least two digits!");
      if (hexStr.length() % 2 != 0)
        throw new NumberFormatException(" Must be even.");
      // remove blanks
      hexStr.trim();
      int lengthOfKey = hexStr.length() / 2;
      bArray= new byte[lengthOfKey];
      for(int i=0; i &lt; lengthOfKey; i++) {
        int actValue = Integer.parseInt(hexStr.substring(2*i,2*i+2), 16); 
        bArray[i] = (byte) actValue;
      }  
    } catch (NumberFormatException e) {
      throw new NumberFormatException("Can't convert key hex value to byte " + 
          "array.\nReason: " + e.getMessage());
    }
    return bArray;
  }