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Configuration file - encrypting connection string

I'm trying to develop a C# Winform application, which connects to SQL database.
So far I was able to move the most sensitive data from my XML configuration file to an external XML configuration file, but that's it.
The last thing I have to do is to encrypt that file, as many people will have access to a directory in which application is located.
My main [APP] configuration file looks as follows:
<?xml version="1.0" encoding="utf-8" ?>
<configuration>
<configSections>
</configSections>
<connectionStrings configSource="conn_string.config"/>
<startup>
<supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.7.2" />
</startup>
</configuration>
And there is my [conn_string] external configuration file in which I'm trying to hide a connection string:
<?xml version="1.0" encoding="utf-8" ?>
<connectionStrings>
<add name="myConnectionStringName"
providerName="System.Data.SqlClient"
connectionString="Data Source=ServerName;Initial
Catalog=InitialDatabaseName;User=UserName;Password=MyPassword;Application Name=MyAppName" />
</connectionStrings>
Now when it comes to encryption I have read that asp-netregiis.exe is looking only for file named "web"
so I temporarily renamed my "conn_string" file to "web"
And tried the encryption(via developer command line VS):
aspnet_regiis -pef "connectionStrings" "path_to_my_conn_string_file"
The result is: ~My translation
The web.config file doesn't contain a configuration tag
So I added one like this:
<?xml version="1.0" encoding="utf-8" ?>
<configuration>
<connectionStrings>
<add name="myConnectionStringName"
providerName="System.Data.SqlClient"
connectionString="Data Source=ServerName;Initial
Catalog=InitialDatabaseName;User=UserName;Password=MyPassword;Application Name=MyAppName" />
</connectionStrings>
</configuration>
Now it complains about: ~Again my translation
File format configSource must be an element conatining section name

The steps you are taking that use aspnet_Regiis are really intended for web applications hosted in Internet Information Server (IIS). The file it is looking for is really "web.config." You mentioned that the app being constructed is a winforms application, which isn't a web application. Regular winforms applications are generally configured via a file called "app.config." Visual Studio may have created a base app.config for you depending on the version you're using.
You can "trick" aspnet_Regiis into encrypting your configuration file by temporarily renaming app.config to web.config, and then invoking aspnet_regiis with a flag that points to the exact path of our "phony" web.config:
For simplicity, let's say your initial app.config resides in c:\MyPrograms\MyApp.
Rename app.config to web.config.
From an administrative command prompt, set your current directory to c:\windows\micrsoft.net\framework\v4.0.30319
Invoke aspnet_regiis, using the "-pef" switch to instruct the tool to encrypt a particular section of your web.config:
aspnet_regiis -pef "connectionStrings" c:\MyPrograms\MyApp
If you see a "Succeeded" message, rename your web.config back to app.config, and run your application. .NET should decrypt your connection string automatically at runtime on that machine.
If you need to put this application on other machines, you may need to consider setting up a common encryption key that can be installed on other machines as well as define a provider in web.config that leverages that key. But for now, let's get the basic process working locally, and then worry about the other components once we know this part is working.
Hope this helps!

Connection string in EF

I’m a student. And this is my first production level project. I’m developing a WPF application using Entity Framework, which will be running only on a tab. I have problem in choosing a database. Since this application is going to run only on one device and cloud database cannot be used, what would be the best option?
If I use mssql the connection string in my development environment and production environment differs. Am I wrong? If I’m right what would be the solution for having a connection string that works identically in both environments.
Thanks in advance.

Usually you always end up with a different connection string for development (ex: without password) and for production (ex: long password).
C# handles this with App.config:
<?xml version="1.0" encoding="utf-8"?>
<configuration>
<connectionStrings>
<add name="yourname" connectionString="..." providerName="MySql.Data.MySqlClient" />
</connectionStrings>
</configuration>
And then you'll add a transformation file that changes certain values of your App.config depending on the environment where you'll deploy it.
Typically there is an App.Release.config file that updates the connectionString when built in Release mode (versus Debug mode)
<?xml version="1.0" encoding="utf-8"?>
<configuration xmlns:xdt="http://schemas.microsoft.com/XML-Document-Transform">
<connectionStrings>
<add name="yourname"
connectionString="productionConnectionStringHere"
xdt:Transform="SetAttributes" xdt:Locator="Match(name)"/>
</connectionStrings>
</configuration>
As to which database you're going to use: It doesn't really matter. Have a look at Sqlite. Or Mongo if you don't have tabular data.

Share config file with multiple project in same solution

My project use Entity Framework 6 Database First for the DAL, and it need to have a connectionString in every project's config file.
As I have multi project in solution, I found that it can be a problem if I need to modify connection string, which I need to check every config file.
So I come up an idea, create a Share config file under the solution directory.
The structure:
+ Solution
- CommonConfig
- Share.Debug.config
- Share.Release.config
- Project1
- web.config
- web.Debug.config
- web.Release.config
- Share.Debug.config (Add with Link)
- Share.Release.config (Add with Link)
- Project2
...
And I have move the connectionString section to Share.xxx.config
<connectionStrings>
<add name="db" connectionString="..." />
</connectionStrings>
First test with configSource, it work without problem
<?xml version="1.0" encoding="utf-8"?>
<configuration>
...
<connectionStrings configSource="bin\Share.Debug.config"/>
...
</configuration>
Then I have remove whole section for connectionString
And modify the web.Debug.config
<?xml version="1.0"?>
<configuration xmlns:xdt="http://schemas.microsoft.com/XML-Document-Transform">
<connectionStrings configSource="bin\Share.Debug.config" xdt:Transform="InsertIfMissing" />
<system.web>
</system.web>
</configuration>
But it doesn't work, the EF cannot find the connectionString with this setting.
Will it a problem if I want to add a whole section instead of a node?
EDIT
After read several post, some said the transform only work when I publish the website, so I try to publish it to my local IIS.
When I create and preview the publish profile, it return error
A section using 'configSource' may contain no other attributes or elements.

app.config file C# winforms preserve the connection string

I have an app.config file in Winforms application that holds a connection string. This is to go out to multiple tenant (clients) as a separate file. These clients have different database sources. This config file also holds other version information such as EF, Telerik reporting etc...
<supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.5.1" />
and
<section name="Telerik.Reporting"
type="Telerik.Reporting.Configuration.ReportingConfigurationSection, Telerik.Reporting, Version=8.1.14.804, Culture=neutral, PublicKeyToken=a9d7983dfcc261be"
allowLocation="true" allowDefinition="Everywhere" />
The problem I have is when we have an updated version of EF or Telerik reporting with our application and we deploy (auto-deploy) this we need to overwrite the app.config file in the client directory to update the versions in the client config file. They then lose their connection setting and I do not want the client to have to go and re-enter it.
My question:
Is there a best practice to overcome this issue? Should I hold the connection string somewhere else?

Yep, the best thing to do is to move your connection strings section to an another config file and reference that file within your app.config.
For example create a new file called connectionStrings.config:
<connectionStrings>
<add name="Default" connectionString="[client_connection_string] "/>
</connectionStrings>
And in your app.config file:
<?xml version="1.0" encoding="utf-8" ?>
<configuration>
<connectionStrings configSource="connectionStrings.config" />
</configuration>
A full example can be found here.

Use an external configuration file that is referenced from the application config file. E.g. include this section in your config file.
<configuration>
<connectionStrings configSource="connections.config"/>
</configuration>
The external config file is described http://msdn.microsoft.com/en-us/library/ms254494(v=vs.110).aspx
Note that storing connection settings in plaintext on a workstation is still a bad idea.
Using Windows registry for stuff like this is a definite no-no these days.

you can try to hold all connection data that you need in separate xml file so it dont get overwrite when you preform a deploy of updated version.

ConfigurationManager does not point to correct app.config

I am trying to use ConfigurationManager to get the connection string from a project call FileShareAccessLibrary.
This is the code I am writting in order to do this:
ConfigurationManager.ConnectionStrings["FileShareAccessLibrary"].ConnectionString
This is the content of app.Config
<?xml version="1.0" encoding="utf-8"?>
<configuration>
<configSections></configSections>
<connectionStrings>
<add name="FileShareAccessLibrary" connectionString="......"
providerName="System.Data.SqlClient" />
<add name="FileShareAccessLibrary.Properties.Settings"
connectionString="..."
providerName="System.Data.SqlClient" />
</connectionStrings>
</configuration>
When I run my app I get a NullReferenceException because ConfigurationManager.ConnectionStrings["FileShareAccessLibrary"] returns null.
While debugging I noticed that none of the two connection strings are stored inside ConfigurationManager.ConnectionStrings so I figured that the ConfigurationManager is pointing to another file.
In my project I have not other app.config file.
Is there something I am doing wrong here?
Why is ConfigurationManager not getting my connection string?

If your FileShareAccessLibrary project is a class library rather than a windows forms application or console application then you will need to move the connection strings (and app settings if you have any) from the FileShareAccessLibrary config file to the config file of the application(s) that reference the FileShareAccessLibrary dll.