Perfect Forward Secrecy - Protecting the gateway to your world

Created on Jul 31 2014, 10:25 AM by Robert Lin

Remember the movie "The Truman Show", where Jim Carrey played the main character of a TV show that chronicled the life of a man who was initially unaware that he was living in a constructed reality television show, broadcast around the clock to billions of people around the globe. Imagine that your organisation is chronicled the same way. Every online transaction, secured or not.

That's what Heartbleed can do.  Fortunately most systems using OpenSSL libraries have been patched (hopefully) to counter this. What if there is another way that this can be done. That this could be happening right now, on a  daily basis and that this is not a vulnerability, but is actually how most clients connect to organisations during SSL/TLS negotitaions for the past decade?

Fristly have a look at how SSL/TLS handshake works. 

Consider this scenario:

A script kiddie downloads Wireshark and uses it to track network activities within your organisation. Entire transations are recorded, including SSL sessions.  Several years later, after gaining much experience, he can now gain access to the servers and the expired Private Key pairs that were once used to encrypt these sessions. These sessions were encrypted with RSA key exchange. He emails the CSO, "I know what you did last summer".

OK. A bit too dramatic and over the top, but perfectly possible. This is the flaw (not vulnerability) when using RSA Key Exchange in SSL/TLS negotiations without proper Key Management. As each session is related to the RSA private key used, recorded sessions can be decrypted later.

An alternative to the RSA key exchange is to use another algorithm, Diffie-Hellman, which creates sessions that are not associated with the private key. Even if the session information is recorded there is no easy way to decipher the computations. With proper Diffie-Hellman implementation, encrypted information cannot be deciphered in the future. This is called Forward Secrecy.

To see how Perfect Forward Secrecy can be be achieved, ready your coffee, get your thinking cap on and start reading the document attached. 

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