title: HMACSHA1.ComputeHash() thread-safety question
body: <p>i am asking myself if it would be dangerous on a asp.net page´s codebehind to use an static (Shared) variable which holds an HMACSHA1-instance. the problem is that the same HMACSHA1-instance would be used by all the asp.net worker-process´ threads when processing multiple simultaneous requests on the same asp.net-page. 
  all (HMACSHA1)instance- and ComputeHash()-method variables which are used/modified by ComputeHash() would be shared (= could be modified) by all the threads?! is that assumption correct? 
  as a result the return value of ComputeHash would not be guaranteed to be correct?!?!
  thus i am not allowed to use an static/Shared HMACSHA1-instance over all the asp.net-threads..</p>
  
  <p>i am just wondering what you think about this problem. </p>
  
  <p>the only solution to this would be sth like an critical path etc in the ComputeHash()-method. but that is "out of our reach"..</p>
  
  <p>regards,
  kris</p>