Hi,
I don't know what is exactly your problem? If you want to encrypt web.config section you can do that easily.
Just use
aspnet_regiis.exe[
^] tool provided with .NET framework...
If you use
google[
^] you can find several solutions on first results page and use any solution to solve your task...
If you want to do that from your code then use methods listed
here[
^] in paragraph named "Programmatically Encrypting Configuration Sections"...
Notice: Make a backup of your web.config before you try this. Just in case... ;)