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Comment by matthewaveryusa | Hacker News Reader

>the Mullvad Browser applies a "hide-in-the-crowd" approach to online privacy by creating a similar fingerprint for all of its users. The browser's 'out-of-the-box' configurations and settings will mask many parameters and features commonly used to extract information from a person's device that can make them identifiable, including fonts, rendered content, and several hardware APIs.

What does masking specifically mean? Is it returning pre-canned responses to those queries that match non mullvad browser users. Because otherwise the absence of these APIs basically fingerprints the user to the Mullvad Browser which, realistically, will always be a small fraction of total browser sessions.

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It is using the same profile as Tor Browser which will broaden the group a little. There has been effort to upstream many of these fingerprinting resistance changes to Firefox, which would broaden the group even more, but I don't know if they are on par yet.

I don't understand why TOR Browser thought that was a good idea either. It seems extremely risky to try to make every browser appear the same and simply hope that they've managed to cover every single means to fingerprint an individual. It's a game of Whac-A-Mole where your adversary is constantly exploring new fingerprinting techniques so TOR/Mullvad has to invest their time and effort into doing the same just so they can counter them all. If they miss anything or don't catch it before or as soon as anyone else does they lose the ability to hide in the crowd entirely.

Some amount of research into fingerprinting techniques will always be needed but it seems to me that a far simpler solution would be to randomize the fingerprint for each connection. It doesn't matter if your browser fingerprint is unique as long as it's always changing. That would also make it harder to detect TOR/Mullvad users since they'll look exactly the same as anyone else with a unique fingerprint. It also gives users the ability to modify some of their fingerprint according to their needs without losing protection. For example, they could freely change their useragent for certain websites/requests while still having a unique fingerprint.

Honest question, what's the upside of not doing this? You're already identified as a Tor user via the IP address. But wouldn't a unique, for example, canvas fingerprint just deanonymize you further? A shared fingerprint just makes you indistinguishable from others Tor users. Which you're already being classified as and can't escape that printing.

IP addresses won't necessarily ID a TOR user unless all exit nodes are known and being checked for. The TOR browser fingerprint stands out like a sore thumb though.

The shared fingerprint makes TOR users indistinguishable from other TOR users unless/until a single identifying factor isn't accounted for at which point all TOR users are identifiable on every connection, across time, different domains, etc. The sameness of TOR user's fingerprints + even just one consistent identifying feature means TOR users could be individually tracked.

A unique canvas fingerprint can be used to track you, but as long as it's differently unique on every request it can't be used to track you because the resulting fingerprint will always be different.

The "hide in the crowd" trick of trying to make a bunch of different people's browsers look identical isn't a bad thing, it's just extremely fragile. Still, it's better than nothing. Making all browsers randomize their fingerprint every time defeats tracking just as well as the "hide in the crowd" trick does (when that trick is 100% perfect) but also adds resilience and flexibility

Tor exit nodes are self-identifying. There’s a DNS-based reverse-IP API you can use to ask if an IP address is a Tor exit node.

Good to know! Weird that stuff like https://www.dan.me.uk/tornodes and https://www.ipqualityscore.com/tor-ip-address-check are still around.

> IP addresses won't necessarily ID a TOR user unless all exit nodes are known and being checked for.

Forgive my naivety, I don't really know Tor that well or even use it, but aren't nearly all exit nodes known and aren't they routinely checked for? It does not seem like a difficult thing to check for. I mean when I googled to check it seems like it is easy and Tor even provides a tool and publishes the 2188 addresses[0,1,2]. So... I'm quite confused about your assumption because a quick googling is leading me to believe that this is a rather known thing and doesn't require anywhere near state level action. I mean people routinely scan the entire internet and those posts don't even make it to HN anymore because they are so easy.

> The shared fingerprint makes TOR users indistinguishable from other TOR users unless/until a single identifying factor isn't accounted for at which point all TOR users are identifiable on every connection, across time, different domains, etc. The sameness of TOR user's fingerprints + even just one consistent identifying feature means TOR users could be individually tracked.

This is a great point, and I get it. But I'm not sure how this is different from normal situation. Doesn't this mean a misconfiguration of the Tor browser? One or two metrics may not be enough entropy to have confidence in an identity, though certainty you're right that it is of concern. I'm just trying to intuit the entropy difference. I'd wager it matters which metric is broken. But the question is when we start undoing Tor fingerprint overrides, at what point does the entropy decease before it starts increasing again? (as you're suggesting) Is that enough information to confidently identify a person? I honestly have no idea. This is a question since you're stating this is a cause for concern.

> A unique canvas fingerprint can be used to track you, but as long as it's differently unique on every request it can't be used to track you because the resulting fingerprint will always be different.

Is that true? I heard that Canvas Fingerprint randomizers actually decrease anonymity for the average user (i.e. done without other measures such as what Tor and Mullvad are doing). Due to noise being information itself, and is thus itself a fingerprint. You just call the function multiple times and look for differences or call different functions and look for similarities (i.e. the return const value). Maybe not as clear of an identifier as a normal canvas fingerprint, but it does constitute good information as most browsers aren't randomizing. I mean one piece of information alone isn't enough, that is why they collect several. You aren't being identified by only your canvas fingerprint.

> isn't a bad thing, it's just extremely fragile. Still, it's better than nothing.

I'm just asking what your alternative is. Btw, Tor and Mullvad __are__ randomizing[3]. So what is your complaint and what is your suggestion?

[0] https://metrics.torproject.org/exonerator.html

[1] https://2019.www.torproject.org/projects/tordnsel.html

[2] https://ipdata.co/blog/tor-detection/

[3] https://mullvad.net/en/browser/hard-facts

> privacy.resistFingerprinting.autoDeclineNoUserInputCanvasPrompts set to true

> privacy.resistFingerprinting.randomDataOnCanvasExtract set to true

> Doesn't this mean a misconfiguration of the Tor browser?

Not necessarily. It'd just mean that someone figured out a novel way to coax some bit of data from the browser that hadn't been considered or adequately accounted for.

> One or two metrics may not be enough entropy to have confidence in an identity, though certainty you're right that it is of concern.

It'd be less worrying if TOR users were more common, but since so few people use TOR at all, and fewer still will use it for any given site/service it means that what would be a low confidence metric for normal traffic might be all you need to track a TOR user.

> I heard that Canvas Fingerprint randomizers actually decrease anonymity for the average user...You aren't being identified by only your canvas fingerprint.

Canvas randomizations are likely to increase uniqueness which is different from increasing the ability to be tracked. If it's implemented in a way that makes it detectable and/or predictable it could increase the likelihood of being trackable depending on the situation. Canvas randomization is useful, just less useful for easily identifiable browsers which document that they do it since it can just be ignored in those cases.

> I'm just asking what your alternative is.

I think it'd be a robust system where many values were randomized in ways that were logical and consistent. For example, a user agent that implies a certain OS would expose a randomized set of values typical to that OS (fonts, drivers, add-ons, GPU, etc) and randomizations would be appropriate (even customizable) by context (session, window, tab, domain, request) so a website making multiple calls to a function would see consistent results while another (unrelated) website would see you as someone else entirely.

This way you'd always appear as a new unique visitor and if someone comes up with some clever trick to expose some new bit of data you'd still be indistinguishable from every other unique visitor with that bit of data. The vast majority of users on the internet are basically always showing up as "randomized" on first visit. It'd mean you could visit the same website 4 days in a row, but each time you'd just show up as someone new who stopped by, browsed around a bit maybe, and then never came back.

The devil's in the details though I guess.

Forgive my pedantry but it's not TOR[1] and never was, this is bordering on painful to read.

[1]: https://support.torproject.org/#about_why-is-it-called-tor

I appreciate the pedantry! It's a habit I should break from. Can we agree at least that it's not as bad as ToR?

As a side note, Tor Browser/Mullvad Browser does randomize canvas (and this changes every time you restart the browser or press New Identity). I don't remember what the reason for randomizing this specific feature is for, maybe it had better compatibility.

Were you intending to respond to me or the parent to my comment. They are the one that said Tor doesn't randomize.

It seems to me whether you're going to make fingerprintable properties be the same or randomize them, you're always going to need to explore every angle. Otherwise a bad actor can just ignore all the properties you randomize and focus on what's left.

Very few data points used in browser fingerprinting are 100% unique to an individual. Multiple data points are combined to form a hash that is unique to an individual. Most people have a unique fingerprint.

You can sort out your TOR browser traffic by user agent then focus on a single data point to track a small number of those users (probably to the individual level because TOR browser traffic is uncommon) but a website can't always know what's been/being randomized and can't separate out the randomized users from everyone else with a unique fingerprint.

The Whac-A-Mole game still exists when you randomize values, right?

To a certain extent. You don't have to make sure you're catching and accounting for 100% of every possible data point that might be collected by a browser if you're randomizing everything else though. Random value + consistent individual value will always produce a changed hash.

Fair enough, it may be more reliable against general/naive approaches like commercial uses though a sufficiently skilled adversary may only consider the fingerprinting techniques they have missed (one specifically targeting TB users).

If you randomize everything that sounds like a pretty identifiable signal tbh. Unless a very large number of people are also performing that randomization. A large number of people specifically in whichever discriminating group you belong to, which might be something out of your control.

You can already tell Mullvad users from their IP address. If their browser only reveals that much, that sounds like a win to me.

good point!

"a similar fingerprint for all of its users", to me, makes it sound like they accept the fact that users will be fingerpritable as Mullvad Browser users (but not more precise than that).

Actually, which other crowd could they even be referring to with "hide-in-the-crowd"?

let's say windows 11 users who use google chrome

Not sure if you're being sarcastic or not, but Windows 11 users who use Google chrome are only really a crowd at the User Agent string level. Chrome allows much deeper fingerprinting.

It's going to be extremely difficult to imitate another browser like that, especially one of a different codebase. Chrome is extremely fingerprintable too.

> What does masking specifically mean?

Here's a complete list of settings and modifications:

https://mullvad.net/en/browser/hard-facts

They seem to be basing the behavior on the Tor Browser which is described here:

https://blog.torproject.org/browser-fingerprinting-introduct...

The Mullvad Browser download page has this to say:

"Strong anti-fingerprinting from the Tor Project

The Tor Project has a proven track record of building a privacy-focused browser. The Mullvad Browser has the same fingerprinting protection as the Tor Browser – it just connects to the internet with (or without) a VPN instead of the Tor Network."

The alternative (faking Chrome or something) is extremely difficult, especially with a different codebase. There's going to be differences. You can tell if someone is using this browser if they're using Tor/Mullvad too. It's just a better option to create a new identity (TB/Mullvad) and put everyone behind that.

considering the difference between the words mask and hide, i would assume it's replacing them with canned values.

Hopefully the values rotate randomly through a common set of values, rather than just making everyone Windows 11/Chrome.

the 'scanner darkly' method, i think xxxterm used to do that

probably more annoying to fingerprint in general, but its own signal in another way

well, each individual browser should not rotate the values to often, every few weeks or months maybe, if at all, or when sessions are cleared. or they could differ per site. but across all browser instances a statistical distribution of values that is similar to the existing distribution would help to ensure that no particular value stands out. given that it is firefox this should also mean that only average firefox values should be used because the browser itself can be detected through checking feature differences which can't be masked as easily.

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