Except in some cases you may have a way of securely communicating the key at an earlier point in time. For example, you generating a 1TB key before leaving on

Except in some cases you may have a way of securely communicating the key at an earlier point in time. For example, you generating a 1TB key before leaving on a trip you could imagine a VPN set up that encrypted 1TB of traffic in a way that was theoretically unbreakable by someone sniffing the traffic only.