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Thank you very much for that expanded explanation. I now know more, but knowledge is a dangerous thing. Let's pretend I have the fastest hash generation engin

Thank you very much for that expanded explanation. I now know more, but knowledge is a dangerous thing. Let's pretend I have the fastest hash generation engine (actually I'd need 2 for this scheme). I would create a real node that uses my engine and becomes part of the node community. Then I create 100 bogus nodes that proxy to my real node. Now I have a large number of nodes that are essentially using my version of "reality" which, in the beginning, is what everyone else says is truth. Meanwhile I'm busy re-writing history to give myself 10 bazillion bitcoins. My other hash engine is recomputing the chain with my bogus history in the background. At some point it catches up with the present. At that point I substitute my bogus chain for the real chain on my main node. My main node is now in disagreement with everyone else's view of reality. My bogus chain also shows up on my 100 other nodes that are proxying my main node. I now have 101 nodes showing my bogus bitcoins. If 101 nodes isn't enough to win the vote then add more bogus nodes until I have 51% of the total nodes. Also, what's to prevent me from adding many real but zero sum transactions to my chain before I tell the world about those transactions? He who has the biggest chain wins. Unrelated thought: quantum computing sounds like it could throw a monkey spanner into the wrench works.

bshanks 10y ago
> If 101 nodes isn't enough to win the vote then add more bogus nodes until I have 51% of the total nodes. You could do that, but it would be expensive. It's not the number of nodes that matters, it's the total computing power of those nodes, because they need to hash faster than the rest of the network. Your nodes, combined, would need to have more computing power than all of the other nodes, combined. If the blockchain you are attacking is popular, the cost of this much computing power would be prohibitive (eg for Bitcoin today [https://gobitcoin.io/tools/cost-51-attack/ https://gobitcoin.io/tools/cost-51-attack/] estimates it would cost around $1 billion for the machines plus $2 million per day for electricity). > Also, what's to prevent me from adding many real but zero sum transactions to my chain before I tell the world about those transactions? He who has the biggest chain wins. Since each block must contain the hash of the previous block, these blocks, although empty of data, still have different hashes. So you have to compute just as many hashes, regardless. > Unrelated thought: quantum computing sounds like it could throw a monkey spanner into the wrench works. Yes, maybe. See [https://en.bitcoin.it/wiki/Quantum_computing_and_Bitcoin https://en.bitcoin.it/wiki/Quantum_computing_and_Bitcoin]

bshanks 10y ago

> If 101 nodes isn't enough to win the vote then add more bogus nodes until I have 51% of the total nodes. You could do that, but it would be expensive. It's not the number of nodes that matters, it's the total computing power of those nodes, because they need to hash faster than the rest of the network. Your nodes, combined, would need to have more computing power than all of the other nodes, combined. If the blockchain you are attacking is popular, the cost of this much computing power would be prohibitive (eg for Bitcoin today [https://gobitcoin.io/tools/cost-51-attack/ https://gobitcoin.io/tools/cost-51-attack/] estimates it would cost around $1 billion for the machines plus $2 million per day for electricity). > Also, what's to prevent me from adding many real but zero sum transactions to my chain before I tell the world about those transactions? He who has the biggest chain wins. Since each block must contain the hash of the previous block, these blocks, although empty of data, still have different hashes. So you have to compute just as many hashes, regardless. > Unrelated thought: quantum computing sounds like it could throw a monkey spanner into the wrench works. Yes, maybe. See [https://en.bitcoin.it/wiki/Quantum_computing_and_Bitcoin https://en.bitcoin.it/wiki/Quantum_computing_and_Bitcoin]