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Yes. A 51% attack is a popular whipping boy. It's not as dangerous as it seems. The price would tank, for sure. But your money won't be gone. And eventually wh

Yes. A 51% attack is a popular whipping boy. It's not as dangerous as it seems. The price would tank, for sure. But your money won't be gone. And eventually when the attack dies down you'll get your wealth back. However, it remains a very interesting way for governments to completely destroy Bitcoin. It's the only way, and they have to do it now before centralized, dedicated mining facilities come online. It would disrupt the price enough and scare away enough people that the threat BTC poses will vanish, at least for awhile. And that will discourage miners from setting up facilities, such that the governments can just beat them again if they have to. But it's already almost impossible. The difference is intent. It's not really much of a problem for a miner to have >51% share. They're there to make money. And Satoshi pointed out they'll probably just keep mining rather than devaluing their own wealth. But an organized, worldwide governmental campaign against cryptos would be another matter.

jancsika 9y ago
> And eventually when the attack dies down you'll get your wealth back. Here's the attack the author is describing: block 42: exchange sends 1 BCH to foo block 42: in secret, BTC meanies solve a different block 42 block 62: foo is comfortable believing the transaction is confirmed, so is the exchange block 62: in secret, BTC meanies are now solving secret branch block 63, or possibly secret branch block 64/65/etc. depending on how much hashing power they have block 123: foo and many others have made transactions, exchange has made many other transactions. Maybe some users transfered out dollars during this time. block 123: BTC meanies reveal their branch, which is at block 130 or whatever, propagate it, and all the BCH nodes accept it as having the greatest total difficulty because that is the rule for how the protocol works block 150: the once secret branch now has twenty confirmations, some of those blocks holding transactions from bona fide BCH users. Maybe the exchange halted trading at block 124 because something looked screwy. Maybe the exchange eats the cost of sending more BCH to the users whose coins "disappeared." Or perhaps the BTC meanies keep their branch secret for several days. The point is the appearance of the secret branch undermines faith that 20 confirmations is enough to confirm a transaction, and the users don't know how to judge what constitutes the canonical state of the blockchain. Avoiding that kind of confusion was a stated goal of the Bitcoin whitepaper. Hm... it occurs to me that such an attack could be even more insidious. I'll call it the "Robinhood Attack." The BTC meanies could begin hashing their secret branch and include all the transactions they see happening on the main chain. Then for each new secret block, they could send the block reward to a random recipient chosen from the transactions on the previous block. When the BTC meanies finally reveal their alternate chain, it gets picked up and includes all the transactions, except the block rewards have now been moved from the miners to the speculators. :) Edit: typo
- sillysaurus3 9y ago
  Sure, but that is still a costly one-time attack. It only affects those who transfer coins, not those who hold them. So if you're holding wealth, it will be safe. It will certainly tank te price for a little bit, but the market will readjust based on the probability that it will happen again. And the theory is that miners would need to choose between spending $180k to execute this attack for a couple hours, causing relatively little damage, or just mining BCH faster than anyone else, which would increase their real-world bottom line. The only one to do this consistently would be a government, probably. It's hard to imagine someone willingly burning $200k mostly for lulz. But I suppose BTC millionaires have more than enough, if they wanted to. Also, why was this article flagged? That's frustrating. It was technical and informative. I don't see a vouch button either.
  - QML 9y ago
    Your wealth may be safe, but what about people's trust in the network? This is an attack on morale. I'm curious to, however, whether a 51% attack has ever been pulled off.

jancsika 9y ago

> And eventually when the attack dies down you'll get your wealth back. Here's the attack the author is describing: block 42: exchange sends 1 BCH to foo block 42: in secret, BTC meanies solve a different block 42 block 62: foo is comfortable believing the transaction is confirmed, so is the exchange block 62: in secret, BTC meanies are now solving secret branch block 63, or possibly secret branch block 64/65/etc. depending on how much hashing power they have block 123: foo and many others have made transactions, exchange has made many other transactions. Maybe some users transfered out dollars during this time. block 123: BTC meanies reveal their branch, which is at block 130 or whatever, propagate it, and all the BCH nodes accept it as having the greatest total difficulty because that is the rule for how the protocol works block 150: the once secret branch now has twenty confirmations, some of those blocks holding transactions from bona fide BCH users. Maybe the exchange halted trading at block 124 because something looked screwy. Maybe the exchange eats the cost of sending more BCH to the users whose coins "disappeared." Or perhaps the BTC meanies keep their branch secret for several days. The point is the appearance of the secret branch undermines faith that 20 confirmations is enough to confirm a transaction, and the users don't know how to judge what constitutes the canonical state of the blockchain. Avoiding that kind of confusion was a stated goal of the Bitcoin whitepaper. Hm... it occurs to me that such an attack could be even more insidious. I'll call it the "Robinhood Attack." The BTC meanies could begin hashing their secret branch and include all the transactions they see happening on the main chain. Then for each new secret block, they could send the block reward to a random recipient chosen from the transactions on the previous block. When the BTC meanies finally reveal their alternate chain, it gets picked up and includes all the transactions, except the block rewards have now been moved from the miners to the speculators. :) Edit: typo

sillysaurus3 9y ago
Sure, but that is still a costly one-time attack. It only affects those who transfer coins, not those who hold them. So if you're holding wealth, it will be safe. It will certainly tank te price for a little bit, but the market will readjust based on the probability that it will happen again. And the theory is that miners would need to choose between spending $180k to execute this attack for a couple hours, causing relatively little damage, or just mining BCH faster than anyone else, which would increase their real-world bottom line. The only one to do this consistently would be a government, probably. It's hard to imagine someone willingly burning $200k mostly for lulz. But I suppose BTC millionaires have more than enough, if they wanted to. Also, why was this article flagged? That's frustrating. It was technical and informative. I don't see a vouch button either.
- QML 9y ago
  Your wealth may be safe, but what about people's trust in the network? This is an attack on morale. I'm curious to, however, whether a 51% attack has ever been pulled off.