Perfect Forward Secrecy in the Netcraft Extension

Netcraft has added a Perfect Forward Secrecy (PFS) indicator to the Netcraft Extension for Firefox, Chrome and Opera. This lets users see which websites would allow encrypted traffic to be decrypted en mass at a later date if the site's private key were to be compromised — a danger previously highlighted by Netcraft in June.

PFS, when implemented correctly, ensures that if the long-term private key of a site served over SSL is compromised, historical encrypted traffic cannot be decrypted in bulk. Instead, an eavesdropper would have to break each individual connection independently, which would be incredibly time consuming.

With the recent revelations from Edward Snowden that the NSA is able to read encrypted internet traffic, PFS support is very desirable for privacy-conscious internet users, particularly in countries that also have key disclosure laws.

Currently, most of the major web browsers make it difficult to tell whether or not a website supports PFS. For example, Chrome, Opera 15, and Internet Explorer display information about the current cipher suite in a pop-up, but checking for PFS support relies on in-depth knowledge. Firefox and Opera 12 display part of the cipher suite in their user interfaces; however, they crucially lack the key exchange mechanism, which means it is not possible for the user to tell whether the site supports PFS. Safari fares the worst, as it does not display any information at all about the current cipher suite.

The Netcraft Extension — which blocks phishing attacks and displays metadata about visited websites — now clearly indicates whether the site you are visiting supports PFS. This is displayed in the user interface as a green tick if the site supports PFS, and a red cross if it does not. In addition, in both Chrome and Opera, a small indicator is displayed beside the Netcraft badge when visiting an SSL site which does not support PFS.

The following screenshots show the PFS indicator in the Netcraft Extension when visiting the DuckDuckGo search engine, which enabled the use of PFS cipher suites after the lack of PFS was highlighted in Netcraft's previous analysis of PFS support.

PFS indicator in the Netcraft Extension for Google Chrome™
(The Opera version looks similar)

PFS indicator in the Netcraft Extension for Firefox

The Netcraft Extension is available for Firefox, Chrome and Opera, and can be downloaded from toolbar.netcraft.com. More information about the PFS indicator can be found on the Netcraft Extension FAQ page.

Note: The new version of the Firefox extension is currently awaiting approval from Mozilla; however, it can be manually installed from the version history page by selecting version 1.8.1.