Securing sensitive parts of App.config/web.config

As a developer, you will undoubtedly work with sensitive information such as passwords. How you handle this information during development is very important. In the past, I have received copies of a client's live database to use for testing. This does pose a very real security risk for your client.

Often, we keep settings in a web.config file (when working with web applications). For this example, though, I will be demonstrating a console application that uses an App.config file. The same logic can be applied to a web.config file too.

Getting ready

Creating a console application is the quickest way to demonstrate this recipe. If, however, you want to follow along using a web application (and securing a web.config file), you can do so.

How to do it…

  1. In the console application, locate the App.config file. This is the file that contains the sensitive data:
    How to do it…
  2. If you open the App.config file, you will see that within the appSettings tag there is a key added called Secret. This information should probably not be in the App.config to start off with. The problem here is that it might be checked into your source control. Imagine that on GitHub?
    <?xml version="1.0" encoding="utf-8"?>
<configuration>
    <startup> 
        <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.6.1"/>
    </startup>
    <appSettings>
      <add key="name" value="Dirk"/>
      <add key="lastname" value="Strauss"/> 
      <add key="Secret" value="letMeIn"/>
    </appSettings>
</configuration>
  3. To overcome this vulnerability, we need to move the sensitive data out of the App.config file into another file. To do this, we specify a path to a file that will contain the sensitive data we want to remove from the App.config file:
    <appSettings file="C:	empsecretsecret.config">

    Note

    You might be wondering, why not simply just encrypt the information? Well, that is a given really. The reason this value is in plain text is just to demonstrate a concept here. You would probably encrypt this value anyway in a real-world situation. You would not, however, want this sensitive information sitting on a server in a code repository somewhere, even if it is encrypted. Be safe, move it out of your solution.

  4. When you have added the path to the secure file, remove the key containing the sensitive information:
    How to do it…
  5. Navigate to the path you specified in the App.config file property. Create your secret.config file and open it up for editing:
    How to do it…
  6. Inside this file, repeat the appSettings section and add the Secret key to it. What happens now is that when your console application runs, it reads the appSettings section in your solution and finds the reference to the secret file. It then looks for the secret file and merges it with the App.config in your solution:
    How to do it…
  7. To see that this merge works, add a reference to your console application:
    How to do it…
  8. Search for and add System.Configuration to your references:
    How to do it…
  9. When you have added the reference, your solution references should look something like this:
    How to do it…
  10. To the top of your Program.cs file, add the following using statement:
    using System.Configuration;
  11. Add the following code to read the Secret key setting from your App.config file. Only this time, it will read the merged file, which is made up of your App.config and your secret.config file:
    string sSecret = ConfigurationManager.AppSettings["Secret"];
Console.WriteLine(sSecret);
Console.ReadLine();
  12. Run your console application and you will see that the sensitive data has been read from the secret.config file, which was merged with the App.config file at runtime:
    How to do it…

How it works…

Something I need to point out here is that this technique will also work for web.config files. If you need to remove sensitive information from your configuration file, move it to another file so that it doesn't get included in your source control check-in or deployment.

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