demos/quickstart/protected/pages/Security/ViewState.page


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<com:TContent ID="body" >

<h1>Viewstate Protection</h1>
<p>
Viewstate lies at the heart of PRADO. Viewstate represents data that can be used to restore pages to the state that is last seen by end users before making the current request. By default, PRADO uses hidden fields to store viewstate information.
</p>
<p>
It is extremely important to ensure that viewstate is not tampered by end users. Without protection, malicious users may inject harmful code into viewstate and unwanted instructions may be performed when page state is being restored on server side.
</p>
<p>
To prevent viewstate from being tampered, PRADO enforces viewstate HMAC (Keyed-Hashing for Message Authentication) check before restoring  viewstate. Such a check can detect if the viewstate has been tampered or not by end users. Should the viewstate is modified, PRADO will stop restoring the viewstate and return an error message.
</p>
<p>
HMAC check requires a private key that should be secret to end users. Developers can either manually specify a key or let PRADO automatically generate a key. Manually specified key is useful when the application runs on a server farm. To do so, configure <tt>TSecurityManager</tt> in application configuration,
</p>
<com:TTextHighlighter Language="xml" CssClass="source">
&lt;modules&gt;
    &lt;module id="security"
        class="TSecurityManager"
        ValidationKey="my private key" /&gt;
&lt;/modules&gt;
</com:TTextHighlighter>
<p>
HMAC check does not prevent end users from reading the viewstate content. An added security measure is to encrypt the viewstate information so that end users cannot decipher it. To enable viewstate encryption, set the <tt>EnableStateEncryption</tt> of pages to true. This can be done in <a href="?page=Configurations.PageConfig">page configurations</a> or in page code. Note, encrypting viewstate may degrade the application performance. A better strategy is to store viewstate on the server side, rather than the default hidden field.
</p>
</com:TContent>