# Cover Your Tracks 'randomized fingerprint' is the wrong goal > Cover Your Tracks praises a randomized fingerprint, but values that change on every load are a signal too. Profiles need one stable, normal browser each. Source: https://mosaicbrowser.com/blog/cover-your-tracks-randomized ## 'Randomized fingerprint' is the wrong goal on Cover Your Tracks Cover Your Tracks praises a randomized fingerprint, but values that change on every load are a signal too. Profiles need one stable, normal browser each. ![18.28: 18.28 bits, and the same 18.28 next time](https://mosaicbrowser.com/covers/cover-your-tracks-randomized.webp) Cover Your Tracks, the EFF's fingerprint test, gives its friendliest label to a browser with a randomized fingerprint. That label is right for what the EFF is testing: whether a tracker can follow one person across the web. It is the wrong goal if you run separate browser profiles, because a fingerprint that changes on every load is something a site can see, and an account whose browser never looks the same twice stands out. For profiles, aim for a normal-looking browser that stays the same. ## What Cover Your Tracks is measuring The test, the successor to the EFF's Panopticlick, runs in two parts. One checks whether your browser blocks tracking ads and invisible trackers. The other reads your fingerprint, the screen, fonts, canvas, WebGL, timezone, language and the rest, and compares it with the browsers it has seen. It reports how many bits of identifying information your fingerprint carries and puts you in one of a few groups: unique, nearly unique, or randomized. Randomized means the test found values that change. Brave is the usual example: its fingerprinting protection adds small changes to values such as canvas and audio readouts, seeded per site and per session, so the same script on two different sites gets two different answers. A tracker that relies on a canvas hash to join a visit to a news site with a visit to a shop gets two hashes and nothing to join. For a single person browsing as themselves, that is a sound defence, and the EFF is right to reward it. The Tor Browser takes the opposite route to the same end, making every copy look alike so that nobody stands out. Both strategies answer "can someone follow me around". Mosaic is a desktop app Email yourself the link and open it on your computer. [How it works: Machines that exist](https://mosaicbrowser.com/features/real-fingerprints) ## A profile is asking a different question A browser profile in an anti-detect browser is meant to be one account's computer. The site that account logs in to is supposed to see the same browser every time it comes back, just as it would if the account really had its own laptop. The question is not "can I be followed" but "do these two accounts look like two different people, and does each one look like the same person tomorrow". Randomization fails the second half. A site that reads canvas twice in one page load and gets two answers has learned that something is rewriting canvas. A site that sees one logged-in account arrive with a new fingerprint on every visit has a fact no ordinary computer produces. FingerprintJS's demo shows the same rule from the other side, and we wrote about it as [a pass with two halves](https://mosaicbrowser.com/blog/fingerprintjs-visitor-id-two-halves): a different visitor ID per profile, and the same ID across two launches of one profile. Profiles that collide can be linked, and a profile whose ID changes every launch looks like a spoofer. The same goes for blocking a value outright. An extension that returns a blank canvas or a fixed fake one is easy to read, as [canvas blocker extensions](https://mosaicbrowser.com/blog/canvas-blocker-extensions) shows: a fresh iframe asks the browser directly and gets the real answer beside the fake one. ## What we count as a pass Cover Your Tracks is one of the public detectors in Mosaic's detection catalogue, in the uniqueness group. The pass we wrote for it says that a "randomized fingerprint" verdict is the wrong goal for us, because randomisation is itself detectable, and asks for a normal-looking browser with entropy in line with a real one: roughly 16 to 18 bits. The measured row read **pass, 18.28 bits of entropy, fingerprint unique**. "Unique" sounds bad and is not: on Cover Your Tracks most desktop browsers come out unique among the browsers the EFF has seen, because a few dozen ordinary values multiply out quickly. What matters is that the number is in the range a real browser produces, and that the next launch of the same profile produces the same browser. Getting that row to read anything at all took two fixes, which is worth knowing if you automate the test yourself. The landing page runs nothing until its button is pressed, so a reader that only loads the page records a poster. And the results page prints a "How to read your report" section before any measurement arrives, so a check that waits for the words "bits of identifying information" fires too early. We wait for a number in front of the word "bits", which only the real result has. ## How Mosaic keeps a profile stable Each profile is drawn from one real device record and keeps it: the same GPU, screen and fonts every launch, with canvas, audio and WebGL noise derived from the profile's own seed rather than drawn per page load. Two profiles differ from each other. One profile does not differ from itself. Repairing a profile's hardware redraws the machine from its own seed and keeps its canvas identity, cookies and locale, so a repair does not turn it into a stranger to the sites it already uses. The values are changed in C++ inside Tesseract Chrome, our own Chromium, so a second read from an iframe or a worker gets the same answer as the first. [Real fingerprints](https://mosaicbrowser.com/features/real-fingerprints) covers how a profile is drawn, and [what a browser fingerprint is](https://mosaicbrowser.com/glossary/browser-fingerprint) lists the values a page can read. ## Questions ### What does "your browser has a randomized fingerprint" mean on Cover Your Tracks? The test read some values twice, or compared them against what it expected, and found that they change. Brave's fingerprinting protection does this on purpose, adding small per-site, per-session changes to values such as canvas and audio. ### Is a randomized fingerprint good for privacy? For one person who wants not to be followed from site to site, it is a reasonable defence. A tracker that sees a new fingerprint on every site cannot join the visits by fingerprint alone. ### Why is a randomized fingerprint bad for separate browser profiles? A profile has to be recognised as the same returning browser by the site it logs in to. If its values change on every load, the site sees one account arriving from a browser that never looks the same twice, which real machines do not do. ### How many bits of identifying information is normal? An ordinary desktop browser usually lands in the high teens on Cover Your Tracks. We aim for a profile that reads like one of those, roughly 16 to 18 bits, and that reads the same on the next launch. ## Related [A FingerprintJS pass has two halves](https://mosaicbrowser.com/blog/fingerprintjs-visitor-id-two-halves): A FingerprintJS visitor ID should differ per profile and hold across launches of one. Colliding ids link profiles; ids that change flag a spoofer. [Why canvas blocker extensions can make you easier to spot](https://mosaicbrowser.com/blog/canvas-blocker-extensions): A canvas blocker extension hides your canvas fingerprint by rewriting methods in page JavaScript, and a fresh iframe reads the rewrite: 33 leaked on one probe. [Machines that exist: fingerprints drawn from real hardware](https://mosaicbrowser.com/features/real-fingerprints): Mosaic draws each profile's GPU, screen, CPU, memory and fonts from one real device, so the parts of a fingerprint agree with each other and with the host. [Browser fingerprint: what a site can read about your machine](https://mosaicbrowser.com/glossary/browser-fingerprint): A browser fingerprint is the set of values a site reads about your browser and computer, which together recognize you without cookies. What goes into one. [Why hCaptcha gives some browsers a puzzle every time](https://mosaicbrowser.com/blog/hcaptcha-image-challenge-every-time): hCaptcha's challenge is its score. A puzzle every time usually means blocked cookies, a crowded VPN exit or a browser whose values disagree with each other. [Why every Mac's Chrome says Mac OS X 10_15_7](https://mosaicbrowser.com/blog/mac-os-x-10-15-7): Chrome froze the macOS version in its User-Agent, so every Mac claims 10.15.7. The real one is in Sec-CH-UA-Platform-Version, a hint sites must ask for. [Why the User-Agent says Windows 10 on Windows 11](https://mosaicbrowser.com/blog/windows-11-user-agent-windows-10): Windows 11 and 10 both send Windows NT 10.0 in the User-Agent. Only the platformVersion client hint, 13 or higher, says Windows 11. [Why Chrome's User-Agent says 0.0.0](https://mosaicbrowser.com/blog/chrome-user-agent-0-0-0): Chrome zeroes everything after the major, so the User-Agent says 0.0.0 and the build moves to Sec-CH-UA-Full-Version-List. A real build in the UA is a tell. ## Mosaic, on your own computer The browser this blog is about: its own Chromium, fingerprints from real machines and a proxy exit per profile. Free holds 3 profiles. Pro is $49 a month for any number. Mosaic is a desktop app Email yourself the link and open it on your computer.