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From the bitcoin wiki: An attacker that controls more than 50% of the network's computing power can, for the time that he is in control, exclude and modify the
by aosmith 12y ago
From the bitcoin wiki:
An attacker that controls more than 50% of the network's computing power can, for the time that he is in control, exclude and modify the ordering of transactions. This allows him to:
Reverse transactions that he sends while he's in control. This has the potential to double-spend transactions that previously had already been seen in the block chain.
Prevent some or all transactions from gaining any confirmations
Prevent some or all other miners from mining any valid blocks
The attacker can't:
Reverse other people's transactions
Prevent transactions from being sent at all (they'll show as 0/unconfirmed)
Change the number of coins generated per block
Create coins out of thin air
Send coins that never belonged to him
- Lerc 12y agoWhat does "in control" mean in this sense? Is that an equivalent expression to "greater than 50%"? Also the "Some or all" doesn't seem very specific. What is the factor that makes some become all?
- jdmichal 12y agoI believe the intention in the phrasing is that they could selectively or universally exercise that action. Not that there is some spectrum of control.
- im3w1l 12y agoYou could theoretically mine your own chain from the genesis block right?
- wmf 12y agoThat won't work due to checkpoints and even if it did work it would be the equivalent of nuking the entire Bitcoin ecosystem. It would be more profitable to do something like extending the current blockchain but charge 1% transaction fees.
- im3w1l 12y agoInteresting. For the benefit of others unfamiliar with this. There is a hardcoded list of checkpoint blocks in the Bitcoin client. Any new chain starting before the last checkpoint will be rejected. https://bitcoin.stackexchange.com/questions/1061/can-a-51-attack-be-detected-and-dealt-with/1065#1065 https://bitcoin.stackexchange.com/questions/1061/can-a-51-at... https://bitcoin.stackexchange.com/questions/3114/which-blocks-get-to-be-checkpoints https://bitcoin.stackexchange.com/questions/3114/which-block...
- TheLoneWolfling 12y agoSo in other words if a 51% attack were to mine starting before a checkpoint block, it would end up "just" hard-forking Bitcoin.
- GhotiFish 12y agoWait. If the attacker did any of that while it was in control, then wouldn't it fail validation for every other bitcoin miner? If they lose their 50% control then they generate invalid blocks. Particularly the part regarding the number of coins generated per block. That one will obviously be wrong.