Quote from: TheFascistMind on October 02, 2014, 12:50:35 PM

I keep trying to posit there are other forms of difficulty attacks that can't be defeated with checkpoints. I been hinting at it for many days now.

Certainly there are. Multipools would be an example, not so much an attack as an unintended consequence of optimal mining.
This has killed coins.

Multipooling is when a large mining pool will mine whatever coin(s) will produce the most revenue in the moment and switch targets as swiftly as possible to optimally mine another coin if the revenue falls. This can have the effect of ramping up the difficulty on a coin when the pool is mining it, and then after it mines a bunch of blocks, dumping them on the market it has effectively reduced the price, and increased the difficulty, making mining that coin less rewarding... it then switches to another coin.

The coin it just left, is then stuck with a difficulty that its normal miners can not easily achieve, and a crashed market for its coins.

There may be other examples, that's the one that pop into my head at the moment.

Quote from: TheFascistMind on October 02, 2014, 12:50:35 PM

What % of hashrate is needed for selfish mining attack?

Theoretically 25-33%. Selfish mining is more difficult to detect with CN coins than some others due to the anonymity features, and the fast block times.

Quote from: TheFascistMind on October 02, 2014, 12:50:35 PM

How much can he amplify his hashrate by hiding it in the 20%?
Remember he said he needed only 20% of the hashrate. Seems obvious to me what he is doing. Wink

Perhaps he can further amplify it by getting miners to join his pools which are gaining an edge in payouts, but I don't assume that is necessary.

I probably do not understand this question very well.

I think you may be asking how much hashrate could be hidden from the difficulty algorithm if it was only used <20% of the time? I think that there isn't a maximum to that.

It is not obvious to me yet what BCX is doing, it is not obvious to me yet that BCX is doing anything at all.

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How will your checkpoints work if his attack catapults his effective hashrate to 51%? He can then ignore the checkpoints and replace with any chain he wants.

If BCX musters >50% there are a lot of things that can be done which would be very harmful and potential coin killers.
Ignoring checkpoints and replacing chains however, is not one of those things.