Trace-the-pattern stroke hugs the ideal path too closely (no hand tremor) or is impossibly fast
bh.arena_pattern_superhuman · convicts
What it catches
Kitsune arena TRACE-THE-PATTERN gate (arena/pattern.go) — the connect-the-dots / Android-pattern-lock family, reproduced as owned infra (no clone/asset). N waypoints are shown; the client draws ONE stroke through them in order (a continuous drag), reporting the sampled [x,y] stroke. The server checks the stroke passes within the hit radius of each waypoint in order, then computes TWO SERVER-OBSERVED tells: (1) PATH FIDELITY (the novel one) — the mean deviation of the stroke from the IDEAL polyline (nearest waypoint-to-waypoint segment for each stroke point). A real hand drawing between dots wobbles (curvature + tremor, several px mean deviation); a synthetic stroke that interpolates the straight segments hugs the ideal path with a mean deviation ~ 0. A deviation below patternStraightPx (1.5px) is a too-straight machine path. (2) SUPERHUMAN SPEED — the whole draw (SERVER-OBSERVED age) faster than N * patternPerWaypoint (300ms), the time a human needs to move the pointer between consecutive waypoints. Either tell -> anomaly:pattern_superhuman; the detector relay (/arena/pattern/verify) joins it to ks_sid so a PASS is CONVICTED on coherence (the arena thesis: the solve-BEHAVIOUR discriminates). A NEW tell family (stroke path-fidelity) distinct from the click-precision / hold-tremor / plan-length gates. FP-SAFE BY CONSTRUCTION: a real hand-drawn stroke always deviates from the ideal line by more than the floor, and the speed floor bounds human pointer-movement time (hardware-independent); a wobbly, time-spending human stroke is silent on both. EXPERIMENTAL (w0.85, calibration: raise patternStraightPx if a careful stylus user draws under it; the RED evader that adds synthetic wobble to its interpolated path beats the fidelity tell but must then also spend the movement time, and an instant draw still trips the speed prong). Test both directions: a straight interpolated stroke (dev ~ 0) or an instant draw convicts; a wobbly hand-drawn stroke that spends the time is silent.
Signals it reads
behavioral.arena_pattern_superhuman
How it fires
present
Bypassed by 10
Frontier evaders that reach the detector uncaught (scored only suspicious, defeating every convicting tell) — this check is not one that stops them. The red-team frontier this detection still has to convict.