API

1. What is API in Browser Fingerprinting

In browser fingerprinting, “API” refers to the collection of JavaScript interfaces and method outputs, which can be uniquely attached to different browsers, versions, extensions, restrictions, or even system-specific behaviors.

Examples include:

• navigator.mediaDevices
• navigator.getBattery()
• window.RTCPeerConnection
• CanvasRenderingContext2D
• WebGLRenderingContext
• AudioContext

These APIs expose:

• Supported capabilities
• Available features
• Whether they are enabled or altered
• Deterministic but sensitive return values — which make them exploitable for browser identification

API-based fingerprinting strategies often bridge the gap between hardware detection and software environments, particularly on site-utils like fingerprintjs.com, major ad platforms, or anti-scraping tools using JS API introspection to detect automation and spoofing.

2. How Platforms Detect API Fingerprints

Each API exposes not just surface-level feature sets but also internal execution results or toString() traces. Some of the most popular methods used in API fingerprint detection include:

1. Function Override Detection: Real browsers return native functions like CanvasRenderingContext2D.prototype.fillText.toString() as '[native code]'. Tools detecting overridden methods may flag spoofed or masked APIs.
2. DOM API Stereotyping: API responses like navigator.userAgent or window.chrome might be checked for expected patterns — even across platforms or contexts.
3. API Accessibility Mapping: Platforms audit which APIs are accessible, non-null, or return cached/system-specific data in order to build a “normative browser behavior model”.
4. System Behavior Reflections:

• AudioContext.sampleRate might reflect real audio output capabilities.
• window.devicePixelRatio might cross-check with display/viewport-related spoofing.

5. API Instance Signatures: Each instance of an API (e.g., new AudioContext()) may generate subtle randomness or uniquely structured contexts which are fingerprinted.

Websites can build high-efficiency fingerprint models by combining results from multiple API calls to reinforce confidence in user identity, especially in scenarios like programmatic advertising, KYC verification, and SaaS security.

3. How FlashID Masks API Fingerprints

FlashID intervenes at the JavaScript API surface layer, allowing not just spoofing values, but the entire semantic tree of browser-exposed API behavior.

FlashID’s API masking includes:

1. Native Code Simulation:

• It replaces overridden functions like fillText or getCurrentPosition with bridges that return 'function fillText() { [native code] }', fooling many basic detection systems.

2. Selective API Access Control:

• FlashID allows customization per profile for which APIs should appear supported, restricted, failed, or masked with simulated response.

3. Instance-Level API Consistency:

• Every API — even on session restore — persists behavior to ensure reproducibility across profiles.

4. Custom Stack Injection & ToString Spoofing:

• toStringTag, Symbol.toStringTag, and target origins are overwritten to maintain coherence.

5. Event Consistency and Callback Simulation:

• FlashID ensures asynchronous and event-based API patterns feel plausible, not scripted.

6. Cross-Profile API Divergence:

• Each profile behaves differently even if running on the same machine. That ensures API diversity, which is crucial for multi-account safety.

7. Interceptor Layer for Modern APIs:

• Supports interception and masking of ongoing APIs like MediaCapabilities, DeviceInfo, and more.

FlashID does not merely spoof individual values — it builds entirely plausible browser identity models for each active session, helping users remain functional and undetectable in platforms that apply API fingerprint correlation.

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