title: ASP.net ViewState encryption and decryption
body: <p>I heard that .NET framework will encrypt the ViewState using SHA1 or some other algorithm.
  So if i know the SHA1 encryption and decryption algorithm can i tamper a ViewState?I mean<br>
  a malicious user studies SHA1 encryption algorithm,if he understand that algorith and develops decryption algorithm ,will it open the road of viewstate tampering? or SHA1 or other algorithm uses any random tricks for encryption and decryption?</p>