[bobvan13]

A one-time pad is the right idea. I would send it on fiber at night before the markets open and then use bits from it as the market trades. A few MB per day would be plenty, given the dialup-like speeds of shortwave. That would go through a 10 gbps fiber in milliseconds.

The actual encryption of each bit just require an XOR on each end of the link. That's about half a nanosecond on a Xeon or one clock cycle on your FPGA.

A jammer wants to be close to the receiving antenna so he can use less power. Yet he wants to be far away so he's less likely to be caught. Willfully interfering with any any radio service is illegal in any regulatory domain AFAIK.

[tripletao]

There is no need for a one-time pad. Any good stream cipher works just as well, same as for any other link. Message integrity is a fun question, since you don't want to spend the bits that you'd need for typical levels of security there; but that question is again independent of a one-time pad vs. normal crypto.

Jamming a licensed radio link vital to rich people who routinely deal with the government doesn't sound like a great idea to me.

[bobvan13]

Good point, a one-time pad is not needed.

Either way, the likelihood of loss between TX and RX means that you can't advance the cipher as bits arrive. I'm thinking you'd have to advance based on GPS-sync'd clocks. Given that each bit is at least 10's of microseconds, GPS sync is plenty good.