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I'm new to cryptocurrencies, so I recently read the paper from the Satoshi Nakamoto ( link is here ) to know a little bit more about the Bitcoin.And I saw this statement:

What is needed is an electronic payment system based on cryptographic proof instead of trust, allowing any two willing parties to transact directly with each other without the need for a trusted third party. Transactions that are computationally impractical to reverse would protect sellers from fraud, and routine escrow mechanisms could easily be implemented to protect buyers. In this paper, we propose a solution to the double-spending problem using a peer-to-peer distributed timestamp server to generate computational proof of the chronological order of transactions. The system is secure as long as honest nodes collectively control more CPU power than any cooperating group of attacker nodes.

So my questions would be:

  1. Could a large botnet disrupt/hack the whole cryptocurrency system if the botnet currently holds more CPU power than the friendly nodes?
  2. If yes,would it be feasible at all and or worth the work?

I may understood this whole idea wrongly, so any tips, advice is appreciated!

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Could a large botnet disrupt/hack the whole cryptocurrency system if the botnet currently holds more CPU power than the friendly nodes?

Yes, this is known as 51% attack. The malicious attacker should control >50 percent of hashing power in the network.

If yes,would it be feasible at all and or worth the work?

Current network hashing power is around 11 million TH/s. So the attacker should buy another 11 million TH/s. Bitcoin Antminer S9 has 14TH/s so you should buy around 800 000 of these. Let's say one is 2000$ so you have to invest 1.6 billion $.

So it is relatively feasible. (Especially when the current bitcoin market capitalization is $136 billion)

Check also: Would any of the current botnets be able to launch and sustain a 51% attack?.

About is it worth it: this depends of what you consider by worth. It will probably make irreparable damage to BTC if 51% attack is successful, is that worth investing 1.6 billion $. You can check if there is similar question of what 51% attacker could achieve (he can not gain 136$ billion of bitcoins) for more info.

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    11 million THps / 14 THps = 785,714 miners. 785714 miners * $2000 each => 1.57 billion dollars – morsecoder Nov 20 '17 at 20:40
  • He has to control only half of 11 million. Actually if all current nodes are honest, he should buy another 11 million to control >50%. – croraf Nov 20 '17 at 20:42
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    @croraf It's not like if you add 5.5 million TH/s then an existing 5.5 million goes away. To get 51% of the hashpower by adding new mining hardware you would have to add just more than is already there. Even if that was right it would be 785 million, not 400 million – morsecoder Nov 20 '17 at 20:45
  • @StephenM347 corrected. – croraf Nov 20 '17 at 20:48

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