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BCH right now has around 10% of BTC total hashrate.
There are multiple pools that control 10%+ of the total BTC hashrate why haven't any of those just allocated a few hours of hashrate to do a 51% attack similar to the one we saw recent on BTG. If they have 10% of BTC hashrate then it would only cost them around $60,000 per hour to control the network (to pay the users using the pool)
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Because of the cost, specifically the opportunity cost.
If a miner has 10% of the BTC hashrate, then if they pointed all of that mining power to BCH, they would still be losing money. With 50% of the hashrate on BCH, they would mine roughly 50% of the blocks in a day, which is 72 blocks. At 12.5 BCH per block,72 * 12.5 = 900 BCH. Convert that to BTC at the current exchange rate (0.135 BTC/BCH) 900 * 0.135 = 121.5 BTC.
However if the miner keeps mining BTC, at 10% of the network hash rate, they would mine ~14 blocks per day. With at least 12.5 BTC per block, a miner would be making 14 * 12.5 = 175 BTC per day, much more than if they were mining BCH.
Thus a miner will earn more money from mining BTC rather than mining BCH. Performing a 51% attack on BCH isn't really worth it; all you can get is possibly some double spends, and less value in BTC.
I understand from that point but they could make way more than 175 BTC in value from attacking multiple exchanges? BTG attackers managed to take several million and that coins daily volume/order books is vastly smaller than BCH. – masterq – 2018-05-27T20:28:34.030
2@masterq you must not ignore the risks and potential costs of being caught attacking multiple exchanges (or simply having your attack fail for some reason). If it is profitable to just mine BTC, why risk your profits? – chytrik – 2018-05-27T21:02:32.897
1Yea that's probably a risk most wont be willing to take but BCH being safe on the notion of no company risking being caught doesn't really make it safe. Plus with the rise of decentralised exchanges wont this just become much easier? – masterq – 2018-05-27T21:07:14.280
One also has to take into account the possibility that performing such an attack will cause the price of the currency targeted by the attack to drop. That would make the attack even less profitable. – kasperd – 2018-05-27T23:03:34.673
@kasperd Yes, maybe worth it may not. If BTG is a example of any then it would defiantly be worth it. – masterq – 2018-05-28T01:44:55.370
Mining profitability doesn't have much to do with 51% attack. If they defraud an exchange for $10 MM, then it's well worth missing out on BTC's blockrewards. – ecurrencyhodler – 2018-05-28T02:26:29.910
when you control 51% of the hash rate, you mine 100% of the blocks, not 51% of the blocks. – hedgedandlevered – 2018-07-30T21:15:47.123