How to encrypt/decrypt the url in C#

I have a URL www.site-address/site-page/page1.aspx?username=deepu&password=deepu
how can i change the URL to
www.site-address/site-page/page1.aspx?username=232322323232&password=2323232322323
ie i want to encrypt the fields i pass through the URL please help me to encrypt and decrypt the URL in C# using .net,now i am using response.redirect and pass these values as query string….pls help….

Navigate back & reload page

I have a problem with the navigation in my ASP.NET (Framework 4) web project. I have a login field on the master-page. The master-page contains also one ContentPlaceHolder which dynamically includes other aspx pages. I start on page “a” and navigate to page “b”. When I log in on page “b”, an additional node in my navigation becomes visible. Now to my problem: When I push the “history-back”-button from the browser the additional node disappears on page “a”.