> 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 n

> 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]