By proof-of-work consensus. This makes attacks costly, basically they have to spend more resources than half the network, hence the name "51% attack". The Bitc

By proof-of-work consensus. This makes attacks costly, basically they have to spend more resources than half the network, hence the name "51% attack". The Bitcoin whitepaper [0] is a very accesible read, but the revolutionary ideas are not immediately obvious. [0] https://www.bitcoin.com/bitcoin.pdf https://www.bitcoin.com/bitcoin.pdf