Quote from: jl2012 on May 06, 2014, 02:43:03 PM

Quote from: cr1776 on May 06, 2014, 01:09:09 PM

Quote from: Evil-Knievel on May 06, 2014, 06:54:00 AM

Quote from: telepatheic on May 05, 2014, 06:47:38 PM

This isn't a bug because chains are selected in terms of cumulative difficulty not length of chain. Very quickly a node can distinguish the real chain from the fakes.

Then it is even easier to perform this attack, in theory.
All you would have to do is create a whole bunch of low-difficulty blocks with nearly the same timestamp, then after the "difficulty adjustment" in your branch of the blockchain would result in a super large difficulty. Solve that one block and the blockchain is broken.

Note cumulative, not last.

He's talking about cumulative, but that's irrelevant. The expected work required for that "super large difficulty block*" equals to the cumulative work of all blocks in the past 5 years

(*ignoring the 4x adjustment rule)

It doesn't seem like he is talking about cumulative difficulty given that he says mine a whole bunch of low-difficulty blocks with nearly the same timestamp and then have a super large difficulty adjustment. The cumulative difficulty (e.g. the sum of the difficulty - each block weighted by difficulty) of his chain would be less than the real chain even with that last super large difficulty adjustment. It appears from his description that he is relying upon the last super large difficulty increase to break the chain. He might have the longest chain, but not the highest cumulative difficulty.

Regardless, there are numerous other issues with it, but the lack of cumulative difficulty being accounted for seems to be one.