Quantum Key Distribution. You can prove that the key hasn't been intercepted. But since that means you need a direct point to point connection with no routers,

Quantum Key Distribution. You can prove that the key hasn't been intercepted. But since that means you need a direct point to point connection with no routers, switches, hubs, amplifiers/repeaters etc., it only works for a tiny fraction of cases. https://en.wikipedia.org/wiki/Quantum_key_distribution https://en.wikipedia.org/wiki/Quantum_key_distribution