Internet Explorer 11 and Perfect-Forward-Secrecy

In case you missed it, the recent Windows 8.1 Update update adds four new ciphersuites (including two supported by Chrome32) and changes the ciphersuite order to prefer algorithms that offer Perfect-Forward-Secrecy. You can read more about this update here.

Wikipedia has a nice article on PFS, but the short summary is as follows:

When your browser makes a HTTPS connection, typically, two keys are used: the client generates a random secret key that is used by a fast, symmetric (“bulk”) encryption algorithm, and it encrypts that secret using the public asymmetric key (slow) provided by the server. The problem is that if the server’s private key is ever compromised, an attacker who had previously recorded your traffic could then decrypt the secret symmetric key and turn the “gibberish” he had recorded back into the plaintext of your web session’s traffic, even if it took place months or years ago.

In PFS, each connection to the server generates a new asymmetric key pair specific to that session, such that if the server’s private key is compromised, only future traffic is at risk of disclosure.

The Windows 8.1 Update isn’t the first time that IE has supported PFS, but the new ciphersuites added in this update have performance characteristics that make servers more likely to use them.