Encrypting App.config For Multiple Machines

As developers, we should all care about security and how we store and use sensitive data, to either connect to the databases or login to domain accounts etc.

Today, I'm going to discuss how to encrypt usernames and passwords that are stored and saved via an application's app.config. This article will use a custom configuration section called EncryptUserCredentials. I won't discuss here how I created that, but here is a sample app.config showing it. Please note.

• service - key value to the record.
• userName - username.
• password - password.

I will not show you the implementation details and how you would access this in code, until another post. Today, we will discuss how you can encrypt the EncyptedUserCredentials themselves, because at the moment they are plain text for all to see!

The way you accomplish this is, by using aspnet_regiis.exe, which, all you ASP.NET web developers already know, registers your web applications with IIS.

But wait. There are other functions dandy binary brings and that is encrypting sections in web.configs.....

But I'm using an App.Config silly:

That's right. That doesn't matter. They are just config files to .NET, but with different names. So, let me explain what you need to do. But before that, here is where aspnet_regiis is located on your Windows box:

Before we move on, I must tell you we are focusing on a multi-machine configuration file encryption using RSA. If your application is running on one machine only, then you can use DPAPI and its provider DataProtectionConfigurationProvider. DPAPI is handled by Windows itself and uses specific machine keys and containers. These are not transferable to different machines. If you wanted to use the DPAPI method for a multi-machine scenario, aspnet_regiis would need to be run on an app.config on each machine it is deployed on.

Why! Is that a bad thing?

Simple. You would need to store a plain text app.config file as either part of the continuous integration process or someone would need to manually keep a copy and run it on each machine, or even include the plain copy in the installer if that was your method for deploying. This just adds a security weak point. You could include scripts to delete the plain text files, if this is the route you wanted to go down. But, just so you know, DPAPI exists and could be a better option for you.

RSA route

So, aspnet_regiis allows you to create containers of asymmetric private/public keys and export them to other machines, allowing you one global config file to be used.

Step 0 - Preperation is (RSA) key

Yes- yes. Step 0 exits because I got half way and forgot this step. Thank the stars, it was meant to be Step1! Add a configProtectedData section to your config with provider. Please note:

• keyContainerName - should be the name of the RSA container you will create later.
• name - Can be anything. Im naming mine MyEncryptionProvider.