Here is the source code to encrypt and decrypt <connectionString> section in Web.config using RSA Protected Configuration provider model.

Note that below source code is from class library file. It is quite feasible to edit the code and use within a button click event as you wish.

Hope you find it useful!!

using System;
using System.Collections.Generic;
using System.Text;
using System.Web;
//specific to configuration
using System.Configuration;
using System.Web.Configuration;
using System.Web.Security;
namespace WebUtils
{
/// <summary>
/// Contains methods for Encrypting and decrypting connectionStrings
/// section in web.config
/// current encryption configuration model is Rsa,
/// it is feasible to change this to DataProtectionConfigurationProvider
/// </summary>
/// <author>Raju Golla</author>
public class EncryptDecrypt
{
//Get Application path using HttpContext
public static string path = HttpContext.Current.
Request.ApplicationPath;
/// <summary>
/// Encrypt web.config connectionStrings
/// section using Rsa protected configuration
/// provider model
/// </summary>
#region Encrypt method
public static void EncryptConnString()
{
Configuration config = WebConfigurationManager.
OpenWebConfiguration(path);
ConfigurationSection section =
config.GetSection("connectionStrings");
if (!section.SectionInformation.IsProtected)
{
section.SectionInformation.ProtectSection
("RsaProtectedConfigurationProvider");
config.Save();
}
}
#endregion
/// <summary>
/// Decrypts connectionStrings section in
///web.config using Rsa provider model
/// </summary>
#region Decrypt method
public static void DecryptConnString()
{
Configuration config = WebConfigurationManager.
OpenWebConfiguration(path);
ConfigurationSection section =
config.GetSection("connectionStrings");
if (section.SectionInformation.IsProtected)
{
section.SectionInformation.UnprotectSection();
config.Save();
}
}
#endregion
}
}

References:

http://msdn.microsoft.com/en-us/library/ms998280.aspx