That paper you link to uses a trusted third party. I highly doubt you could run a 51% attack for any significant amount of time on $20MM. Consider the coins b

That paper you link to uses a trusted third party. I highly doubt you could run a 51% attack for any significant amount of time on $20MM. Consider the coins being mined everyday are worth ~500,000USD. That is not to say it is impossible, but there is almost no way anyone in the world could pull it off for $20MM except the people who already have ASIC designs.