Model binder to decrypt string and convert to int

Question

I have a model which has a property id of type int .

I pass the id in the url like Detail/20 for fetching the data. But, now my customer says they don't want to see the id , since any one can modify and see other records.

Now, I've decided to encrypt and decrypt it, and assign it to another property: encId .

public ActionResult List()
{
    foreach(Employee e in empList)
    {
        e.encId = MyUtil.Encrypt(id,"sessionid");    
    }

    return View(empList);
}

Finally, I make my url like Detail/WOgV16ZKsShQY4nF3REcNQ==/ .

Now, all I need is to decrypt it back to the original form and assign it to the property id of type int .

public ActionResult Detail(int id) //don't want (string id)
{

}

How can I write my model binder that decrypt and convert it to valid id ? Also if any error/exception occurs, it has to redirect to 404 Error page. It might happen when user manually edits some useless text in the url (encrypted id).

Answer 1

First, this is not the way to go about securing your website and data. Please take a look at the issues with Security Through Obscurity . You would be better off defining sets of permissions on each employee record and who can or cannot edit them. Such an example could look like this:

public ActionResult Detail(int id)
{
    if(MySecurityProvider.CanView(id, HttpContext.Current.User.Identity.Name){
        return View();
    }
    Return RedirectToAction("PermissionIssue", "Errors");
}

With that said, to continue on the path you are on, simply do the decryption within the action result.

public ActionResult Detail(string Id)
{
    int actualId;
    try{
       actualId = MyUtil.Decrypt(id);
    }catch(Exception e){
         //someone mucked with my encryption string
         RedirectToAction("SomeError", "Errors");
    }
    var employee = MyEmployeeService.GetEmployeeById(actualId);
    if(employee == null){
         //This was a bad id
         RedirectToAction("NotFound", "Errors");
    }
    Return View(employee);
}