timing channel visualizer

even a do-nothing browser tab does not run smoothly. requestAnimationFrame is the highest-priority callback the page has, yet between frames the os, gpu, other tabs, and v8’s gc all steal time. tap below to record 4 seconds of frame deltas and see what your system looks like to a timer.

top: ms between frames over 4s · bottom: histogram of frame deltas. spikes are the scheduler talking.

a transmitter inside the same tab encodes each bit as a busy-loop or an idle slot. a receiver running on the same thread cannot read shared memory and has no api access to the transmitter. it only watches frame deltas. the resulting timing pattern is enough to recover characters of text — illustrating why isolated origins are not actually isolated against a careful scheduler.

• spectre & meltdown turned cpu cache timing into the largest disclosure in chip history. browsers patched performance.now to ms granularity in response.
• cross-origin tabs share a thread or a cpu core. one tab’s render burst is another tab’s missed frame — and that pattern can encode information.
• full isolation is rare: site isolation puts origins in different processes, but they still contend for cpu, memory bandwidth, and gpu queues.
• this demo is intra-tab for clarity — the same channel works between iframes, service workers, and audio worklets, with progressively smaller bandwidth.