Mining a longest fork and maintaining it is probable if you have more than 50%. If you have less than 50%, there is still a chance, but eventually, the main chain will catch up.
For example, even if I'm a pool with 25% of mining power, I could still occasionally find 2 blocks in a row. But I won't maintain that lead because in general, over time, for every 1 block I find, 3 other blocks will be found.
It looks like this paper's technique is to take advantage of those temporary situations where one pool is lucky enough to get ahead.
For example, even if I'm a pool with 25% of mining power, I could still occasionally find 2 blocks in a row. But I won't maintain that lead because in general, over time, for every 1 block I find, 3 other blocks will be found.
It looks like this paper's technique is to take advantage of those temporary situations where one pool is lucky enough to get ahead.