Storing and Reading Base64 Encoded Connection String in Web.Config
Introduction
Many people store database connection string in web.config file. However, web.config file being an XML file, the data stored there is in clear text format. This is especially important for connection strings because anybody can easily see your database details including user id and password. In this article we will see how you can encrypt values stored in web.config using Base64 encoding and later on decrypt them in your code. Note that Base64 encoding is not a secure algorithm but it is a quick and easy way to hide the connection string details from casual readers.
Storing custom values in web.config
You store custom configuration values in web.config using section. The section looks like this:
<appSettings>
<add key="connectionstring"
value="data source=.\vsdotnet;initial
catalog=Northwind;user id=sa;password=mypassword"/>
</appSettings>
In short you store key-value pairs inside the section.
Encrypting connection string
In order to encrypt above connection string we will be using System.Convert class. We will build a small console application that allows us to pass plain connection string as command line argument and then displays encrypted version on the console.
The code looks like this:

Public Shared Sub Main(args() As String)
Dim data() As Byte = System.Text.ASCIIEncoding.ASCII.GetBytes(args(0))
Dim str As String = Convert.ToBase64String(data)
Console.WriteLine(str)
End Sub
Here, we are using System.Text.ASCIIEncoding.ASCII class to convert the connection string to an array of bytes. This is necessary because the Convert class function ToBase64String() expects array of bytes and then returns Base64 encoded version of it.
You can invoke above application (I created it as Base64Encrypter.exe) at command prompt like this:

Base64Encrypter.exe "data source=.\vsdotnet;initial catalog=Northwind;user id=sa;password=mypassword"
The output will be:
ZGF0YSBzb3VyY2U9Llx2c2RvdG5ldDtpbml0aWFsIGNhdGFsb2c9Tm9ydGh3aW5kO3VzZXIgaWQ9c2E7
cGFzc3dvcmQ9bXlwYXNzd29yZA==

You can now copy-paste this encoded version of the connection string in the web.config. The new appSettings section will look like this:
<appSettings>
<add key="connectionstring" value="ZGF0YSBzb3VyY2U9Llx2c2RvdG5ldDtpbml0aWFsIGNhdGFsb2c9Tm9ydGh3aW5kO3VzZXIgaWQ9c2E7
cGFzc3dvcmQ9bXlwYXNzd29yZA=="/>
</appSettings>

Reading the encrypted connection string back

Now, let us see how we can read the encrypted connection string and decrypt it so that we can use it further.


Dim data() As Byte = Convert.FromBase64String
(ConfigurationSettings.AppSettings("connectionstring"))
str = System.Text.ASCIIEncoding.ASCII.GetString(data)


Here, we again used the Convert class and called its FromBase64String function. This function accepts Base64 encoded string and returns a byte array. In order to retrieve the appSetting value we used ConfigurationSettings class as shown above. Finally, we used ASCII class again to convert the byte array to a string.