Fonts

1. What is Font Fingerprinting

Font fingerprinting refers to the technique of enumerating and identifying the list of fonts available in a user’s system through methods like:

• document.fonts API
• Font size/width rendering consistency (timing or pixel-based detection)
• Flash or CSS-based font probing
• Font support detection using Canvas and measuring text rendering differences

While not tied to a particular API (unlike WebGL or Battery), font availability can vary significantly between devices, making it a soft indicator of user uniqueness.

It’s commonly used in combination with other fingerprints (Canvas, User-Agent, OS, Language) to improve browser matching accuracy, especially in:

• KYC and identity platforms
• Multi-accounting detection systems
• Web session collusion detection

2. How Platforms Fingerprint Font Availability

Anti-fraud and ad-tech systems often hook into one or multiple of the following:

• document.fonts.keys() and check(): Enumerates whether a font is supported and ready to use in the browser.
• Canvas Font Rendering: By drawing text with specific fonts and measuring rendered output, fonts can be indirectly identified.
• System Font Injection Detection: Some heuristics detect whether fonts were injected by tools like Puppeteer, via font names or family accessibility.
• Font Subsetting & Loading Timing: The timing of when a font becomes “available” or “unavailable” can be used to detect browser automation footprints.
• CSS @font-face Probing: Systems may load a known webfont and inspect how the browser handles fallback rendering or timing to infer internal browser configurations.

Websites can build a derived profile from fonts to enhance device uniqueness — detecting anomalies such as:

• “Too many system fonts” or “None”
• Fonts inconsistent with location or reported OS
• Unusual blacklisted or flagged fonts (like helper fonts used in spoofers)

3. How FlashID Makes Font Fingerprints Safe and Consistent

FlashID controls and fingerprints all aspects of font rendering behavior to ensure browser profiles appear consistent, realistic, and unique.

Here’s how FlashID masks or simulates fonts:

1. Font List Isolation: Each browser profile maintains its own font list independent of the underlying host system. Hidden system fonts can be mimicked to reflect any geo or OS region.
2. Canvas Text Spoofing Algorithm: FlashID precisely alters text width and glyph style fallback values during Canvas rendering to simulate specific font lists — even in headless or protected profiles.
3. document.fonts Control:

• Simulated FontFaceSet signatures
• Control over check() return values
• Mocking of font load timing / delays

4. Font Name Obfuscation: FlashID may rename system fonts (e.g., “Arial” to “Calibri”) to avoid deterministic matching while ensuring realistic distribution and rendering behavior.
5. Cross-OS Font Mimicking: FlashID allows font lists that mimic other operating systems, helping break platform-font correlations.
6. Font Order Randomization: Font query order is randomized per browser instance to avoid statistical re-identification through sorting or accessibility patterns.
7. No Glyph Drawing Protection: Some platforms detect active browser automation by observing whether glyph drawing happens in background mode. FlashID emulates correct drawing behavior and font permissions live.

By offering full control of font fingerprinting surfaces, FlashID ensures browser profiles remain safe from unified identification triggered by passive font analysis and backend collusion models.

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