It's not a one-time pad being distributed, because leaking the pad leaks all your communications. It's almost certainly the actual messages being distributed, at specific times of day. The listener records the numbers for the known time period to get the message, then decodes it with their pad for that period. Then they destroy that pad. Continually broadcasting numbers makes it impossible to tell the length of the messages.

One time pads work only if only the sender and receiver have a copy of the pad - and they destroy each sheet on use. Distributing the pads is hard, but often it can be done easier than the message.

Distributing a one time pad like this is a stupid idea: it isn't hard to collect everything you ever send, and it takes a computer a few ms to check every encrypted message against every possible sequence. That is breaking a distribute one time pad via shortwave like this is something a single layperson can do, it doesn't even need a government scale attacker to break it.

Don't get me wrong, this can be used for good encryption. However it isn't a one time pad they are doing, it is something more complex.

And it is faster than the internet. That's why high speed traders are starting to use HF.

https://spectrum.ieee.org/wall-street-tries-shortwave-radio-...