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There’s been a number of articles recently about perfect forward secrecy (PFS). The main aim of PFS is to ensure that even if the private SSL/TLS key for www.fastmail.fm was ever compromised, it would still be impossible to decrypt any existing captured traffic between users and our server. If you’re looking for more information, the linked articles above are worth reading to get a better overview. For PFS to work, both the server (us) and the client (your web browser) must support it.
Fastmail has supported PFS via ECDHE for some time now (since July 2012). Unfortunately a few browsers don’t support ECDHE.
Today we’ve updated our ciphers to the best practice recommended by SSL Labs. Using the SSL Labs site tester on www.fastmail.fm shows that we now support PFS on all major browsers except for IE 8 on Windows XP, which has no support for PFS and so can never support it.
We’re pretty sure that this change won’t have any compatibility issues with old clients (which should fall back to older ciphers), but we’ll keep an eye out in case there’s any reported problems.