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It's a stable hash derived from the ",[212,213,214],"a",{"href":102},"signals"," Rupt collects: the user agent, hardware probes, cryptographic measurements, storage state, and behavioral indicators. The same browser on the same machine, fingerprinted twice, produces the same fingerprint. A different browser on the same machine produces a different fingerprint.",[208,217,218,219,222],{},"Fingerprints sit between sessions (which are ephemeral) and ",[212,220,221],{"href":138},"devices"," (which are physical). Multiple fingerprints can map to one device, Chrome and Safari on the same Mac, for example. One fingerprint maps to exactly one browser instance.",[224,225,227],"h2",{"id":226},"what-fingerprints-are-good-for","What fingerprints are good for",[229,230,231,240,246],"ul",{},[232,233,234,239],"li",{},[235,236,237],"strong",{},[212,238,169],{"href":170},": multiple user accounts sharing a single fingerprint usually means one person operating multiple accounts.",[232,241,242,245],{},[235,243,244],{},"Multi-accounting and ban evasion",": clearing cookies doesn't clear a fingerprint. Someone trying to re-create an account after being blocked will trip on fingerprint reuse.",[232,247,248,251],{},[235,249,250],{},"Account takeover detection",": a login from a brand-new fingerprint, when the user has been on the same one for months, is a meaningful shift.",[208,253,254,255,258],{},"These are surfaced through ",[212,256,257],{"href":106},"checks",":",[229,260,261,268],{},[232,262,263,267],{},[264,265,266],"code",{},"is_new_fingerprint",": first time this fingerprint is seen for this user.",[232,269,270,273],{},[264,271,272],{},"fingerprint_user_count",": how many users share this fingerprint.",[224,275,277],{"id":276},"differentiating-within-a-browser-not-across","Differentiating within a browser, not across",[208,279,280,281,285],{},"Fingerprinting is intra-browser by design. The goal isn't to recognize the same person whether they switch from Chrome to Safari, which is privacy-violating and unreliable. The goal is ",[282,283,284],"em",{},"within"," a single browser, to differentiate this instance from every other instance, even if they look superficially similar.",[208,287,288],{},"What matters for accuracy: that the same browser produces the same fingerprint on every visit, and that two genuinely different browsers don't collide. Cross-browser uniformity isn't the goal.",[224,290,292],{"id":291},"anti-fingerprinting-tooling","Anti-fingerprinting tooling",[208,294,295,296,299,300,303],{},"Some browsers and extensions actively try to defeat fingerprinting: Tor Browser, Brave's farbling, Firefox's RFP, Safari's ITP lockdown. Rupt detects this directly: the ",[264,297,298],{},"anti_fingerprinting"," ",[212,301,302],{"href":110},"risk"," surfaces when these tools are in play, regardless of whether they successfully obscured the underlying signals. That gives you policy options ranging from \"ignore\" (privacy-friendly product) to \"challenge\" (high-trust flow).",{"title":305,"searchDepth":306,"depth":306,"links":307},"",2,[308,309,310],{"id":226,"depth":306,"text":227},{"id":276,"depth":306,"text":277},{"id":291,"depth":306,"text":292},"A fingerprint is a browser-level identity, a stable hash derived from a browser's signals. Narrower than a device, broader than a session.","md",{},true,"---\ntitle: Fingerprints\ndescription: A fingerprint is a browser-level identity, a stable hash derived from a browser's signals. Narrower than a device, broader than a session.\n---\n\n# Fingerprints\n\nA fingerprint is a browser-level identity in Rupt's data model. It's a stable hash derived from the [signals](\u002Fdocs\u002Fv3\u002Fconcepts\u002Fsignals) Rupt collects: the user agent, hardware probes, cryptographic measurements, storage state, and behavioral indicators. The same browser on the same machine, fingerprinted twice, produces the same fingerprint. A different browser on the same machine produces a different fingerprint.\n\nFingerprints sit between sessions (which are ephemeral) and [devices](\u002Fdocs\u002Fv3\u002Fconcepts\u002Fdevices) (which are physical). Multiple fingerprints can map to one device, Chrome and Safari on the same Mac, for example. One fingerprint maps to exactly one browser instance.\n\n## What fingerprints are good for\n\n- **[Linked accounts](\u002Fdocs\u002Fv3\u002Fconcepts\u002Flinked-accounts)**: multiple user accounts sharing a single fingerprint usually means one person operating multiple accounts.\n- **Multi-accounting and ban evasion**: clearing cookies doesn't clear a fingerprint. Someone trying to re-create an account after being blocked will trip on fingerprint reuse.\n- **Account takeover detection**: a login from a brand-new fingerprint, when the user has been on the same one for months, is a meaningful shift.\n\nThese are surfaced through [checks](\u002Fdocs\u002Fv3\u002Fconcepts\u002Fchecks):\n\n- `is_new_fingerprint`: first time this fingerprint is seen for this user.\n- `fingerprint_user_count`: how many users share this fingerprint.\n\n## Differentiating within a browser, not across\n\nFingerprinting is intra-browser by design. The goal isn't to recognize the same person whether they switch from Chrome to Safari, which is privacy-violating and unreliable. The goal is _within_ a single browser, to differentiate this instance from every other instance, even if they look superficially similar.\n\nWhat matters for accuracy: that the same browser produces the same fingerprint on every visit, and that two genuinely different browsers don't collide. Cross-browser uniformity isn't the goal.\n\n## Anti-fingerprinting tooling\n\nSome browsers and extensions actively try to defeat fingerprinting: Tor Browser, Brave's farbling, Firefox's RFP, Safari's ITP lockdown. Rupt detects this directly: the `anti_fingerprinting` [risk](\u002Fdocs\u002Fv3\u002Fconcepts\u002Frisks) surfaces when these tools are in play, regardless of whether they successfully obscured the underlying signals. That gives you policy options ranging from \"ignore\" (privacy-friendly product) to \"challenge\" (high-trust flow).\n",{"title":141,"description":311},"YYfusvEKebcO7TpkjqTzqQ34_wRLnfjCF2SPcSdcRPY",1780344893497]