title: How does perfect forward secrecy (PFS) work
body: <p>I'm in an infosec class and I stumbled upon this concept online and it intrigued me.  I've also looked at a few websites and wikipedia that explain the concept, as well as a few posts on stackoverflow, but I'm still getting confused.  From what I understand is in a typical HTTPS public key exchange, a browser and a server come together with keys to create a session key...if someone ever obtained a private key that derived the session key, they could see all the data that was sent between this connection, even in the past.  </p>
  
  <p>My understanding is that with PFS, the 'session key' is never sent , even in encrypted form.  It is kept secret so that even if someone found a private key, they wouldn't be able to access encrypted recorded information from the past.  Is this correct?</p>
  
  <p>I also was wondering, If I am partaking in a PFS exchange  call me "A", with a server "B", PFS is supposed to work with the fact that if my key becomes compromised, A and B's conversation wont become compromised because they don't know the session key.  But how does "B" authenticate me as "A", if my key has in fact became compromised...e.g. how would it know the difference between me (A) or another user (C) using my key attempting to access the data.</p>