It is a super accurate way of timing packet receipt. For keystrokes sent across a WAN that wouldn't normally help you. But this really isn't about ssh, which is

It is a super accurate way of timing packet receipt. For keystrokes sent across a WAN that wouldn't normally help you. But this really isn't about ssh, which is just used as a cute demo of the power of traffic analysis and side channels; this is about remote access to local side channels in the memory system.