C# – 安全地连接到远程SQL Server？

SqlConnection sqlConnection = this.sqlcon();

SqlCommand insertCommand = new SqlCommand("use " + database_telecaster.ToString() + " SELECT Top 1  sid from dbo.Item order by sid desc",sqlConnection);

sqlConnection.Open();
insertCommand.ExecuteNonQuery();

SqlDataReader reader = insertCommand.ExecuteReader();

while (reader.Read())
{
    MaxSid = (reader.GetInt64(0) + 100).ToString();
}
reader.Close();
sqlConnection.Close();

SQL Server con函数：

public SqlConnection sqlcon()
{
    var doc = new XPathDocument(Application.StartupPath + "/DBConn.xml");
    var navigator = doc.CreateNavigator();

    var serverName = navigator.SelectSingleNode("//appsettings/servername");

    var username = navigator.SelectSingleNode("//appsettings/username");
    var password = navigator.SelectSingleNode("//appsettings/password");
    var database = navigator.SelectSingleNode("//appsettings/database");

    object[] objArray = new object[] {
            serverName,database,username,password 
    };

    return new SqlConnection(string.Format("Data Source={0};Initial Catalog={1};User Id={2};Password={3};MultipleActiveResultSets = True",objArray));
}

假设SQL Server安装在Windows VPS上,我将把我的软件提供给不同的人,我希望他们都能访问该SQL服务器……如何在不打开SQL Server端口的情况下做到这一点？因为据我所知,打开端口会导致被黑客入侵,因为所有人都可以远程连接到该服务器.