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Comment by nirvana | Hacker News Reader

Would you mind describing that attack in a bit more detail?

Bitcoin uses a proof of work system to determine the valid chain of transactions, as well as who gets the initial currency payout. Basically, anyone who controls more than 50% of the CPU power in the Bitcoin network can control the currency.

If you want more details, I'd recommend reading the Bitcoin paper: http://bitcoin.org/bitcoin.pdf

Some of the various forks have tried to work around this by having trusted nodes and the like, but then you lose the decentralized nature and are vulnerable to the trusted nodes going rogue.

Having greater than 50% of the computing power of the bitcoin network does not give you complete power of the currency. You would be able to prevent transactions from occurring, and double-spend recent transactions. Since the bitcoin network is effectively the most powerful supercomputer in the world, this would be a very expensive attack to sustain, without that large of a payoff.

I definitely wouldn't recommend starting with the official bitcoin paper to learn about this. That would be like telling a math student to just read Newton if they want to learn Calculus :). Check out the bitcoin wiki instead: https://en.bitcoin.it/wiki/Weaknesses#Attacker_has_a_lot_of_...

FWIW, when I was figuring out Bitcoin I avoided the paper at first (due to logic similar to yours) but eventually read it because there was a lot of noise in the wiki, etc (may have changed). I found it surprisingly accessible; more so than the vast majority of academic papers I've come across (I have most of an EE degree but little to no formal CS training).

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