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measure: truthful scorecard (platform-aware cohort + real control baseline) #43

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Merged
mdheller merged 1 commit into from
Jun 22, 2026
Merged

measure: truthful scorecard (platform-aware cohort + real control baseline) #43

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25 changes: 22 additions & 3 deletions scripts/measure-fingerprint.mjs
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Original file line number Diff line number Diff line change
Expand Up @@ -231,8 +231,14 @@ async function collect(prefs) {
const VECTORS = [
// cohort: a matcher; if the hardened value matches, it's a uniform RFP cohort
// value (good) even when identical to control — NOT a device leak.
{ key: 'userAgent', label: 'User-Agent', kind: 'mask', cohort: (a) => /Mac OS X 10\.15;.*Firefox\/\d+\.0$/.test(a) },
{ key: 'platform', label: 'navigator.platform', kind: 'mask', cohort: (a) => a === 'MacIntel' },
// RFP presents a per-OS uniform cohort UA. A build is judged against ITS OWN
// OS cohort (Mac/Windows/Linux), not hardcoded Mac — otherwise a Linux build
// is wrongly flagged for reporting Linux. (tor-mode forces the Windows cohort
// on all platforms via the OS-spoof patch; that's covered by the Windows arm.)
{ key: 'userAgent', label: 'User-Agent', kind: 'mask',
cohort: (a) => /(Macintosh; Intel Mac OS X 10\.15|Windows NT 10\.0; Win64; x64|X11; Linux x86_64);.*Firefox\/\d+\.0$/.test(a) },
{ key: 'platform', label: 'navigator.platform', kind: 'mask',
cohort: (a) => a === 'MacIntel' || a === 'Win32' || a === 'Linux x86_64' },
{ key: 'hardwareConcurrency', label: 'hardwareConcurrency', kind: 'fixed', expect: 2 },
{ key: 'deviceMemory', label: 'deviceMemory', kind: 'fixed', expect: 'undefined' },
{ key: 'maxTouchPoints', label: 'maxTouchPoints', kind: 'fixed', expect: 0 },
Expand Down Expand Up @@ -271,10 +277,23 @@ function classify(v, control, h1, h2) {

const GOOD = new Set(['NORMALIZED', 'RANDOMIZED', 'MATCHES-COHORT']);

// A --bin build BAKES the hardening into its autoconfig defaults, so an empty-pref
// "control" still runs hardened (control == hardened) and every `mask` vector
// wrongly scores as not-normalized. Force a TRUE unhardened baseline by turning
// off the baked-in protections (these are default prefs, so user prefs override).
const CONTROL_PREFS = {
'privacy.resistFingerprinting': false,
'privacy.fingerprintingProtection': false,
'privacy.fingerprintingProtection.overrides': '',
'privacy.resistFingerprinting.letterboxing': false,
'font.system.whitelist': '',
'gfx.bundled-fonts.activate': 0,
};

(async () => {
const prefs = profilePrefs(profile);
process.stderr.write(`launching Gecko x3 (control + ${profile} x2)...\n`);
const control = await collect({});
const control = await collect(CONTROL_PREFS);
const h1 = await collect(prefs);
const h2 = await collect(prefs);

Expand Down
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