Encrypting or Hiding Strings sent in the url

[mizlfhb]

I am trying to send a Topic name in the URL like,\[code\]<a href="http://stackoverflow.com/questions/3620473/hello?TopicN=blahblahblha">\[/code\]and then output the topic name as the Forum topic title. But the problem is the user can just change the name if they want which doesnt do any harm since I dont really do anything with teh name but I was wondering is there a way to encrypt or swap the letters so its not so obvious what the topicN is ?I also tried md5 encryption but, md5 is only 1 way so that doesnt help. Could use sessions, not sure since i store user login details in sessions,any ideas and examples would be helpful,Thank you