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WebGL Farbling - Profile-Based System

Overview

Brave's WebGL farbling system now uses 10 realistic Apple Silicon GPU profiles instead of random 8-character strings. This provides better fingerprinting resistance while maintaining plausible deniability.

Implementation Date

2026-02-07: Migrated from random string generation to profile-based farbling system.

Profiles

GL_VENDOR (Fixed)

All profiles return the same vendor string:

Google Inc. (Apple)

This matches the format that Chrome/ANGLE returns on macOS with Apple Silicon.

GL_RENDERER (10 Variants)

The system randomly selects one of these 10 profiles using the master seed:

  1. ANGLE (Apple, ANGLE Metal Renderer: Apple M1 Pro, Unspecified Version)
  2. ANGLE (Apple, ANGLE Metal Renderer: Apple M1, Unspecified Version)
  3. ANGLE (Apple, ANGLE Metal Renderer: Apple M2 Pro, Unspecified Version)
  4. ANGLE (Apple, ANGLE Metal Renderer: Apple M2, Unspecified Version)
  5. ANGLE (Apple, ANGLE Metal Renderer: Apple M3 Max, Unspecified Version)
  6. ANGLE (Apple, ANGLE Metal Renderer: Apple M3 Pro, Unspecified Version)
  7. ANGLE (Apple, ANGLE Metal Renderer: Apple M3, Unspecified Version)
  8. ANGLE (Apple, ANGLE Metal Renderer: Apple M4 Pro, Unspecified Version)
  9. ANGLE (Apple, ANGLE Metal Renderer: Apple M4, Unspecified Version)
  10. ANGLE (Apple, ANGLE Metal Renderer: Apple M5, Unspecified Version)

How It Works

1. Profile Selection Algorithm

FarblingPRNG prng = MakePseudoRandomGenerator(FarbleKey::kWebGLRenderer);
size_t profile_index = prng() % 10;  // Select one of 10 profiles

2. Deterministic Selection

The PRNG is seeded with:

  • Master seed (if set via setFingerprintingSeed())
  • eTLD+1 domain (for cross-site isolation)
  • FarbleKey::kWebGLRenderer (specific to this farbling context)

3. Token Derivation

Token = HMAC-SHA256(master_seed, eTLD+1)
Profile = profiles[PRNG(Token, FarbleKey::kWebGLRenderer) % 10]

Key Features

✅ Deterministic

Same master seed + same domain → same profile every time

✅ Per-Context Isolation

  • Same seed, different domains → different profiles (eTLD+1 salting)
  • Different contexts can have independent fingerprints

✅ Realistic Profiles

All profiles are real Apple Silicon GPUs that exist in the wild:

  • M1, M1 Pro (2020-2021)
  • M2, M2 Pro (2022-2023)
  • M3, M3 Pro, M3 Max (2023-2024)
  • M4, M4 Pro (2024-2025)
  • M5 (future-proofing)

✅ No Hardcoded Validation

Chromium/ANGLE doesn't validate GPU strings against any list—they trust OS/driver values

Master Seed Integration

JavaScript API

// Set master seed for this context
window.setFingerprintingSeed(12345);

// Query WebGL
const canvas = document.createElement('canvas');
const gl = canvas.getContext('webgl');
const ext = gl.getExtension('WEBGL_debug_renderer_info');

console.log(gl.getParameter(ext.UNMASKED_VENDOR_WEBGL));
// → "Google Inc. (Apple)"

console.log(gl.getParameter(ext.UNMASKED_RENDERER_WEBGL));
// → "ANGLE (Apple, ANGLE Metal Renderer: Apple M2 Pro, Unspecified Version)"

Consistency Test

// Test 1: Set seed 12345
window.setFingerprintingSeed(12345);
// Reload page → Profile X

// Test 2: Set same seed again
window.setFingerprintingSeed(12345);
// Reload page → Profile X (same as before)

// Test 3: Different seed
window.setFingerprintingSeed(67890);
// Reload page → Profile Y (different from X)

Implementation Files

1. FarbleKey Enum

File: src/brave/third_party/blink/renderer/core/farbling/brave_session_cache.h

enum FarbleKey : uint64_t {
  // ... existing keys
  kWebGLVendor,      // NEW
  kWebGLRenderer,    // NEW
  kKeyCount
};

2. Profile Selection Methods

File: src/brave/third_party/blink/renderer/core/farbling/brave_session_cache.h

blink::String GetFarbledWebGLVendor();
blink::String GetFarbledWebGLRenderer();

3. Profile Implementation

File: src/brave/third_party/blink/renderer/core/farbling/brave_session_cache.cc

blink::String BraveSessionCache::GetFarbledWebGLVendor() {
  return "Google Inc. (Apple)";
}

blink::String BraveSessionCache::GetFarbledWebGLRenderer() {
  static constexpr const char* kWebGLRendererProfiles[] = {
    // ... 10 profiles
  };
  FarblingPRNG prng = MakePseudoRandomGenerator(FarbleKey::kWebGLRenderer);
  return blink::String(kWebGLRendererProfiles[prng() % 10]);
}

4. WebGL Hook

File: src/brave/chromium_src/third_party/blink/renderer/modules/webgl/webgl_rendering_context_base.cc

#define BRAVE_WEBGL_GET_PARAMETER_UNMASKED_RENDERER \
  if (ExtensionEnabled(kWebGLDebugRendererInfoName) && \
      !AllowFingerprintingForHost(Host())) \
    return WebGLAny(script_state, \
        brave::BraveSessionCache::From( \
            *(Host()->GetTopExecutionContext())) \
            .GetFarbledWebGLRenderer());

Statistics

Profile Distribution

With a uniform random distribution across seeds:

  • Each profile: ~10% probability
  • Total combinations: 10 profiles

This is significantly fewer than the previous system (62^8 = 218 trillion combinations), but:

  1. ✅ More realistic (all are real GPUs)
  2. ✅ Harder to detect as fake
  3. ✅ Still provides meaningful anonymity set

Comparison to Previous System

Aspect Old System (Random Strings) New System (Profiles)
Vendor Random 8-char string "Google Inc. (Apple)"
Renderer Random 8-char string 10 realistic profiles
Combinations 62^8 = 218 trillion 10
Detectability Easy (obviously fake) Hard (real GPUs)
Plausibility Low High

Why This Approach?

1. No Validation in Chromium

Research shows Chromium/ANGLE never validates GPU strings against hardcoded lists:

  • Vendor/renderer come from Metal API at runtime (MTLDevice.name)
  • Browser trusts whatever the OS/driver returns
  • No allowlist/blocklist of valid GPU names

2. Realistic Distribution

Using real Apple Silicon GPUs means:

  • Fingerprints blend into real user population
  • Harder for sites to detect farbling
  • More plausible deniability

3. Future-Proof

Includes M4 and M5 (unreleased as of 2024) to ensure longevity

Testing

See WEBGL_FARBLING_TEST.html for interactive tests.

Manual Test

# Open Brave with shields enabled
brave --enable-features=BraveShields

# Open test page
open WEBGL_FARBLING_TEST.html

# Check console
# Should show one of 10 Apple Silicon profiles

Test with Master Seed

// In console
window.setFingerprintingSeed(12345);
location.reload();

// Check GL_RENDERER - should be deterministic
const canvas = document.createElement('canvas');
const gl = canvas.getContext('webgl');
const ext = gl.getExtension('WEBGL_debug_renderer_info');
console.log(gl.getParameter(ext.UNMASKED_RENDERER_WEBGL));

Cross-Site Isolation

The system uses eTLD+1 normalization to ensure subdomains get the same profile:

example.com      → Token_A → Profile 3
www.example.com  → Token_A → Profile 3 (same)
api.example.com  → Token_A → Profile 3 (same)
different.org    → Token_B → Profile 7 (different)

This prevents cross-site tracking while maintaining consistent fingerprints within the same site.

References

Git History

  • 2026-02-07: Implemented profile-based WebGL farbling with 10 Apple Silicon variants
  • Previous: Used random 8-character alphanumeric strings