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A window wider than the screen it claims
ARMANOS टीम6 min
One line finds it
A page can read the screen a browser claims and the window it is looking through. Both are ordinary properties, available to any script without a permission prompt.
On a page that declares a viewport, a window wider than the screen describes a machine that does not exist. Without that line a real phone lays out wider than its screen too, so the comparison is only worth making after it.
- 1
Asks for the screen
Width and height of the display the browser reports.
- 2
Asks for the window
Width and height of the area the page is drawn in.
- 3
Compares them
A window larger than the display is a contradiction inside one browser.
What we measured
Screens are drawn from the profile seed, so we drew 900 desktop profiles of the current fingerprint generation and counted what came out.
Eighteen distinct screens appeared, from 1280 by 720 to 3840 by 2160. That spread is the whole point: a pool of one size would be a signal of its own.
| Measured on 900 draws | Share |
|---|---|
| Screens narrower or shorter than 1920 by 1080 | 64 percent |
| Screens shorter than a 820 point window | 16 percent |
| Distinct screens in the pool | 18 |
| Narrowest and widest | 1280 by 720 and 3840 by 2160 |
Why the numbers land where they do
A person works on the display they own, and a common one is 1920 by 1080. Maximise a window there and it fills that size regardless of what the profile inside it claims.
So the share that disagrees is simply the share of the pool smaller than the display in front of the person. On a larger display it is higher, on a smaller one lower.
A phone makes it obvious
On a phone profile the gap is impossible to miss: a handset claims 360 points across, and a window stretched by hand would be three times that.
That is why a phone window is sized to the handset and a remembered size is not restored for it. The desktop case is the same contradiction with smaller numbers.
What the app does with it
The size a window opens at is capped by the screen the profile claims. A smaller window stays small: the cap is a ceiling, not a requirement.
The outer window is what gets capped, and a page reads the inner area, which is always smaller. The margin works in the profile's favour.
- 1
One function decides
Every window of a profile asks the same code for its size.
- 2
The claim is the ceiling
Width and height are cut down to the screen the profile reports.
- 3
A phone is exact
A handset window equals the handset screen rather than merely fitting inside it.
How to check your own
Open any browser console and read the screen and the window side by side. The comparison takes one line and needs nothing installed.
Do it in a maximised window and in a small one. A profile that answers honestly gives a window no larger than the screen in both.
What this does not claim
- It does not claim that matching sizes make a profile safe. It removes one contradiction out of many, and behaviour, payment details and the history of the account remain untouched by any browser.
- It does not claim that every site checks this. Some do, some never look, and none of them publish what they check.
- The self-test inside the app runs this comparison for a profile with touch, not for a desktop one. Extending it to desktop changes the number of checks the app reports, so it waits for the next acceptance run on a built engine.
- The numbers above describe our pool of screens, drawn on the generation current today. A different pool gives different shares.
Where you can see this yourself
Every number above comes out of code you can open and run.
- The screens are drawn from the profile seed
- packages/shared/src/index.js
- The size of a profile window is decided in one place
- apps/desktop/src/lib/окноПрофиля.js
- The rule is executed against real fingerprints, not read as text
- apps/desktop/test/окно-не-шире-экрана.js
- A phone window is sized to the handset
- apps/desktop/src/lib/mobileEmulation.js · apps/desktop/src/lib/mobileWindow.js
Questions
- Why not give every profile the largest screen?
- One size for everyone is a signal of its own, and a screen far from the machines a platform usually sees stands out on its own.
- Does the person lose the window size they chose?
- Only the part above the claimed screen. A window smaller than the screen opens exactly as it was left.
- Is this about full screen mode?
- No. Full screen makes the window equal to the display, and the contradiction appears only when the window is larger than what the profile claims.
- Can a site tell how the numbers were capped?
- It reads two ordinary values and cannot see what produced them. What it can see is whether they agree.
- Does a proxy change any of this?
- No. The address arrives from elsewhere, and both of these numbers are produced on the machine in front of you.
See what your own browser answers
The check reads 12 values and sends nothing anywhere.