When lawmakers and cops propose banning working cryptography (as they often do in the USA), or ban it outright (as they just did in Australia), they are long on talk about "responsible encryption" and the ability of sufficiently motivated technologists to "figure it out" and very short on how that might work — but after many years, thanks to the UK's spy agency MI5, we have a detailed plan of what this system would look like, and it's called "ghost users."