I'm not trying to diminish the discovery, it's quite the contrary, I think its simplicity and elegance is what makes it so impressive. It's a very elegant solution to a very complex problem and you could explain it in a few minute to somebody with the right technical background.
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That class of actor can even potentially avoid the financial sunk costs that would ordinarily be required, although that in turn would require the use of several zero-day exploits and/or the use of similarly high-value resources usually available only to state-level actors.
Still, under certain circumstances I could see something along these lines being the opening move in World War IV (not to be overly dramatic or anything). Or perhaps a much smaller conflict, should any state be foolish enough to standardize on a national cryptocurrency of their own creation for internal use.
No, not really. The way proof-of-work is used is nothing like in HashCash (more generally known as a time lock puzzle), the solution to a decentralized clock is the one piece that is new. In the paper it is referred to as "Timestamp Server". Everything else is previously known tech, but the clock piece is an invention, the invention that made it all possible.