title: simple yet secure encrypt / decrypt asp to asp.net
body: <p>I have a ASP/VB6 web-app that logs in a user. I want to encrypt the users identity field and pass(querystring) it to a asp.net app and then decrypt it to do a db lookup.</p>
  
  <p>I've googled it and found rot13, albeit not secure enough. I've also found some hits on MD5 / RC4, but did not find any good examples of encrypt / decrypt.</p>
  
  <p>Any ideas on how to implement secure encryption/description logic?</p>