Canvas fingerprinting and Evercookies are two relatively unknown methods for spying on the surfing habits of Internet users. We asked Florian Drechsler, eCommerce expert, web designer, and co-owner of headtrip.io GbR from Nuremberg, Germany, [12], for his assessment of future developments and how to best protect yourself as an Internet surfer.

Linux Magazine: Canvas fingerprinting on web pages first attracted greater attention last summer, when researchers at the universities of Leuven and Princeton provided evidence of this tracking method on almost six percent of all surveyed web sites. Since then, public interest in this technique has again waned somewhat. Based on your experience, are there signs that canvas fingerprints are increasingly being used to identify surfers and their surfing habits on the Internet?

Florian Drechsler: Definitely, yes. The registered percentage of affected websites at that time was attributed to a large extent to advertising service provider AddThis, who apparently used canvas fingerprints to deliver personalized ads. But, AddThis quickly responded to the criticism and removed the canvasing code. In my experience, canvas fingerprinting has definitely spread – simply because many eCommerce companies and advertising platforms see it as a possibility to boost conversion rates through personalized content.

LM: The Tor Browser warns users about canvas fingerprints on many web pages. Often, also the Firefox CanvasBlocker extension indicates that canvas elements are trying to extract image files that could be used for spying on surfers. Analysis of the source code on most affected web pages show that the canvas code causing the alert was attributable to a small script introduced in WordPress 4.2 that checks to see whether emojis are available. Do such extensions that allow visitors to websites to be spied on cause any real danger?

FD: The Emoji script itself is harmless. Instead, the danger lies in the fact that the user approves this innocuous usage of the canvas element, and thus allows other potentially malicious elements.

LM: How can surfers tell, when they are notified of canvas fingerprints, whether those elements are used for tracking?

FD: If you cannot analyze the code yourself, your only option – as is so often the case in Internet security – is to rely on common sense. To do this, however, you need to know how a canvas element works. Canvas elements are used by websites for drawing, say, 3D animations or for browser games. In case of doubt, you should block the canvas element and then try to use the site: Are you missing some elaborate graphics? If so, switch the canvas back on. But if the site works without a canvas element, then it was at least superfluous, or it was actually used to track users.

LM: Evercookies are a tracking method that is as difficult to control as canvas fingerprints. How can I protect myself against Evercookies?

FD: By installing the Firefox BetterPrivacy [13] extension, which deletes Flash cookies and runs the browser in private browsing mode. If you do not need plugins like Silverlight and Flash, you should turn them off – and not only because of the Evercookies. The safest method, however, is the use of a specially hardened Linux distribution such as Tails [14].

LM: How do you see future developments: Are Evercookies and canvas fingerprints likely to spread?

FD: The final version of HTML5 is now only a few months old, and it might take some time until all clients can use canvas elements at all. The more frequently canvas elements are used, the more attractive options for using canvas fingerprinting will become. Evercookies have been around for over five years and are still in active development. Other methods that allow storage of user data might also arise through exploiting new browser technologies. Online traders, in particular, benefit from Evercookies and canvas fingerprinting, which let them trace the surfing behavior of potential customers. I would assume this option is used by increasing numbers of eCommerce companies.