ASP.NET: HttpModule for Query String Encryption

You  can protect URL parameters by using following HttpModule.

If you get the error "Invalid length for a Base-64 char array" when using Convert. FromBase64String(InputString)

Use following:

When Crypted, replace "+" to space.

string encryptString = Convert.ToBase64String(ms.ToArray());

encryptString = encryptString.Replace("+", " ");
http://madskristensen.net/post/HttpModule-for-query-string-encryption.aspx

In addition Scott Mitchel provides a way to implement expiring web pages on your website which can be useful in some situations\
http://aspnet.4guysfromrolla.com/articles/090705-1.aspx

cheers
samitha