To protect a web application from query string manipulation, I was considering adding a query string parameter to every url which stores a SHA1 hash of all the other query string parameters & values, then validating against the hash on every request.

Does this method provide strong protection against user manipulation of query string values? Are there any other downsides/side-effects to doing this?

I am not particularly concerned about the 'ugly' urls for this private web application. Url's will still be 'bookmarkable' as the hash will always be the same for the same query string arguments.

This is an ASP.NET application.