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You're correct that cooperation is key and that if you get "enough" people (50% of hashing power in most cases) behind a plan, they can change the rules of the

You're correct that cooperation is key and that if you get "enough" people (50% of hashing power in most cases) behind a plan, they can change the rules of the game. This could be used to steal coins. This has actually happened in the past. When massive amounts of Ethereum were stolen from the DAO, the community got together and decided that those coins did not belong to the hacker. With >50% of the network, they forked the coin and created a refund contract where people could retrieve their stolen coins.[1] The dissenters remained to form what is now Ethereum Classic. So, what prevents this from happening in a malicious way? The first hurdle is building that consensus. Many people involved in cryptocurrencies today believe that the future value is much higher than today's value. Paying them off would not be easy, especially considering that cashing out a large sum would crash the price of the coins, and thus the profits from your maneuver. That being said, a core assumption of cryptocurrencies is that 50%+ of the network is not malicious. Another way of looking at this is that whoever controls greater than 50% of the network cannot be considered malicious from the network's perspective. They are they consensus. The last point I'll make is speculative. If you created (or took over) a cryptocurrency and built consensus out of malicious actors, what value do you think the outside world would place on that coin? You would win lots of coins, but would anybody pay you dollars for them? [1] https://www.cryptocompare.com/coins/guides/the-dao-the-hack-the-soft-fork-and-the-hard-fork/ https://www.cryptocompare.com/coins/guides/the-dao-the-hack-...

sharemywin 9y ago
Now sell your coins...bitcoin is only worth something if it works. you'd also have to get bunch of people that have invested most of their lives to it.
- fixermark 9y ago
  ... unless the end goal is not to generate profit, but to diminish value represented as BTC by undermining fundamental faith in the network, in which case, a value drop is working as intended.
hackinthebochs 9y ago
> Another way of looking at this is that whoever controls greater than 50% of the network cannot be considered malicious from the network's perspective. What people forget about in these imagined 50% attack scenarios is that 50% attacks only work if the attacking nodes generate valid blocks. All the hashpower in the world doesn't matter if your blocks do not pass validation. So no consortium can just start mining bad blocks and get away with it. The problem is that there are a non-trivial amount of clients that don't do any validation themselves and so rely on full nodes to tell them the true state of the network. Those clients would be subject to losing money. But any big exchange should be validating blocks themselves so the risk to the entire network is minimal to non-existent.

sharemywin 9y ago

Now sell your coins...bitcoin is only worth something if it works. you'd also have to get bunch of people that have invested most of their lives to it.

fixermark 9y ago
... unless the end goal is not to generate profit, but to diminish value represented as BTC by undermining fundamental faith in the network, in which case, a value drop is working as intended.

hackinthebochs 9y ago

> Another way of looking at this is that whoever controls greater than 50% of the network cannot be considered malicious from the network's perspective. What people forget about in these imagined 50% attack scenarios is that 50% attacks only work if the attacking nodes generate valid blocks. All the hashpower in the world doesn't matter if your blocks do not pass validation. So no consortium can just start mining bad blocks and get away with it. The problem is that there are a non-trivial amount of clients that don't do any validation themselves and so rely on full nodes to tell them the true state of the network. Those clients would be subject to losing money. But any big exchange should be validating blocks themselves so the risk to the entire network is minimal to non-existent.