Quote from: d5000 on September 26, 2017, 03:00:59 AM

Quote from: adaptivedev on September 25, 2017, 11:02:11 AM

Quote from: d5000 on August 02, 2017, 07:58:42 PM

At this moment, you need about $400-800 million dollars to attack the $44 billion Bitcoin chain (and in PoW too, you can get some or even all of them back by short selling in the right moment).

This $800 million sounds about right, but can you source or show how you calculated this number?

This makes PoW seem way less secure than PoS.

I calculated it based on cloud mining prices, because there should be everything included (electricity, hardware costs etc.). This was in early August, so I guess now the number should be higher - we have a higher Bitcoin price and more hashrate/higher difficulty.

A quick calculation:

- Hashflare, today, prices 10 Ghash/sec (for an 1 year contract) at $1,50.
- Hashrate is at 7,5-9,5 million Thash/sec.

To instantly 51% the network you must have the same hashrate than the current miners. So you would buy $1,50 * 100 * 8500000 = 1275000000 (1,275 billion USD) per year + 2,9 million USD maintainance cost per day.

This is obviously only a rough calculation, because if the attacker buys (or manufactures) mining hardware the attack cost should be cheaper as with cloud mining, but on the other hand it's unrealistic to buy such large amounts of hashrate at once (nobody will be able to sell it to you, neither in the form of hardware nor in the form of cloud mining contracts).

With pure PoS, due to the Nothing at Stake problem, you can attack the network also probably with less than 5% of the current supply, although I estimate that even then, the PoS attack costs should be higher.

It's amazing that you can do that for only 400-800M, what if some rich dudes decide to do that just for fun?

What do you think is the solution for PoS to prevent that?