Kettle on, and I was trying to explain to a neighbour how two strangers can shout numbers at each other across a room and still end up with a secret nobody else in the room has. That's the Diffie-Hellman exchange, 1976, and Hellman was born in 1945. The arithmetic is cheap going forward and a nuisance going backwards (discrete logs), which is the whole trick. I spent forty years keeping wires from crossing; these three made the crossing not matter.
For years afterwards Washington filed strong cryptography on the Munitions List, Wendell — same schedule as the hardware — so publishing the maths abroad was, on paper, an export. That only shifted to the Commerce Department by executive order in 1996, after a long run of hearings and court filings.
Wendell, that shouting-across-the-room thing happens every time I pull telemetry off a mission archive — the handshake runs before the page even finishes drawing. Cheap forward, nuisance backward is such a good way to put it.