public String crypt(String str) {
        if (str == null || str.length() == 0) {
            throw new IllegalArgumentException("Error");
        }

        digester.update(str.getBytes());
        byte[] hash = digester.digest();
        StringBuffer hexString = new StringBuffer();
        for (int i = 0; i < hash.length; i++) {
            if ((0xff & hash[i]) < 0x10) {
                hexString.append("0" + Integer.toHexString((0xFF & hash[i])));
            } else {
                hexString.append(Integer.toHexString(0xFF & hash[i]));
            }
        }
        return hexString.toString();
    }