Fingerprinting v3: Dark Mode detection

[pes10k]

New CSS features allow sites to determine if your OS or environment is configured for Dark Mode (or similar names). See CSS Media Queries Level 5

We should disable this detection for users wanting the highest level of fingerprinting protection ("strict").

default protections: no changes
max protections: always report that the user prefers "light"

[stephendonner]

@ShivanKaul @pes10k when you get a chance, can you add a testcase/testplan to brave/brave-core#8832? Thanks!

[pes10k]

No problem, here ya go: https://dev-pages.brave.software/fingerprinting/strict-mode.html

The values for the strict mode row should accurately report whether the system has dark mode enabled with default fingerprinting protections, and should always report "dark mode not detected" (regardless of system settings) in strict mode

[stephendonner]

Verified PASSED using

Brave	1.27.65 Chromium: 91.0.4472.101 (Official Build) nightly (x86_64)
Revision	af52a90bf87030dd1523486a1cd3ae25c5d76c9b-refs/branch-heads/4472@{#1462}
OS	macOS Version 11.4 (Build 20F71)

Steps:

1. enabled Dark mode via System Preferences -> General -> Appearance
2. loaded https://dev-pages.brave.software/fingerprinting/strict-mode.html
3. clicked on Generate Values
4. clicked on This Frame, Local Frame and Remote Frame hash values
5. confirmed detected dark mode displayed for Shields off/Allow all fingerprinting, and standard fingerprinting settings
6. confirmed dark mode not detected displayed for strict fingerprinting setting
7. repeated the above for https://dev-pages.bravesoftware.com/fingerprinting/strict-mode.html

https://dev-pages.brave.software/fingerprinting/strict-mode.html

standard fingerprinting	strict fingerprinting

https://dev-pages.bravesoftware.com/fingerprinting/strict-mode.html

standard fingerprinting	strict fingerprinting

---

Verification passed on

Brave | 1.27.78 Chromium: 91.0.4472.114 (Official Build) beta (64-bit)
-- | --
Revision | 4bb19460e8d88c3446b360b0df8fd991fee49c0b-refs/branch-heads/4472@{#1496}
OS | Windows 10 OS Version 2004 (Build 19041.1052)

https://dev-pages.brave.software/fingerprinting/strict-mode.html

standard fingerprinting	strict fingerprinting

https://dev-pages.bravesoftware.com/fingerprinting/strict-mode.html

standard fingerprinting	strict fingerprinting

---

Verified passed with

Brave	1.27.89 Chromium: 91.0.4472.124 (Official Build) beta (64-bit)
Revision	7345a6d1bfcaff81162a957e9b7d52649fe2ac38-refs/branch-heads/4472_114@{#6}
OS	Linux

https://dev-pages.brave.software/fingerprinting/strict-mode.html

This Frame - Std FP	Local Frame - Std FP	Remote Frame - Std FP	This Frame - Strict FP	Local Frame - Strict FP	Remote Frame - Strict FP

https://dev-pages.bravesoftware.com/fingerprinting/strict-mode.html

This Frame - Std FP	Local Frame - Std FP	Remote Frame - Std FP	This Frame - Strict FP	Local Frame - Strict FP	Remote Frame - Strict FP

[iam-cult]

I don't know how others feel, but personally I would not appreciate this feature. Detecting dark mode seems like an overall good thing, as a site can adjust to your preferences, and serve the right favicon for best visibility. It's one of the reasons I don't use Firefox's RFP (That and the timezone spoofing), and it doesn't seem like it's that big of a deal. Sure, it can factor in to your fingerprint. But it's a binary measurement, on or off, and from what I've seen, it's fairly 50/50. If you're faking everything else, this seems like something you can let slide, as, by itself, it provides very little fingerprintable surface.

[srirambv]

Verification passed on OnePlus 6T with Android 10 running 1.27.75 x64 Beta build

• Verified dark mode is detected when fingerprint is set to standard
• Verified dark mode is not detected when fingerprint is set to strict
• Verified setting theme to dark manually works fine
• Verified setting device theme to dark and browser theme to use system default, sets browser to dark theme and dark theme recognition works fine as expected

https://dev-pages.bravesoftware.com/fingerprinting/strict-mode.html

Fingerprint (Strict)	Fingerprint (Standard)

https://dev-pages.brave.software/fingerprinting/strict-mode.html

Fingerprint (Strict)	Fingerprint (Standard)

---

Verification passed on Samsung Tab A with Android 10 running 1.27.75 x64 Beta build

• Verified dark mode is detected when fingerprint is set to standard
• Verified dark mode is not detected when fingerprint is set to strict
• Verified setting theme to dark manually works fine
• Verified setting device theme to dark and browser theme to use system default, sets browser to dark theme and dark theme recognition works fine as expected

https://dev-pages.bravesoftware.com/fingerprinting/strict-mode.html

Fingerprint (Strict)	Fingerprint (Standard)

https://dev-pages.brave.software/fingerprinting/strict-mode.html

Fingerprint (Strict)	Fingerprint (Standard)