Quote from: AlexR12 on December 07, 2017, 05:50:26 PM

Quote from: AdolfinWolf on December 06, 2017, 08:35:18 PM

Because it can only choose to not confirm/confirm certain transactions, it CAN'T decide for example that all the coins should be sent to the miner's adress.

I would say that "modifying" is the wrong word, rather changing/excluding certain transactions..

These are some better sources:

https://en.bitcoin.it/wiki/Weaknesses#Attacker_has_a_lot_of_computing_power
https://bitcoin.stackexchange.com/questions/658/what-can-an-attacker-with-51-of-hash-power-do

I assume by "it" you mean "an attacker". It seems to me a bit clear now, but... just to make sure I understand it right. Based on my understanding of Satoshi's paper it follows that 51% attacker will be able to extend any block in the chain with probability 1 (provided the attacker has unlimited resources). Is this true?
And my second question: according to your first link:"...exclude and modify the ordering of transactions". What is the attacker's gain of changing the ordering of transactions?

Thanks!

One needs to find a correct hash to claim a block. Once you have done this work you need to do it again, again in order for your block to become the longest and for other miners to consider you branch to be the correct one. If you have half the hash power of the entire network you would expect to get every other block (over time) but, with half the hashpower. it is not inconceivable for you to get 5 blocks in a row (1:32) or even 10 in a row (1:1024).

Today, 2017, it's virtually impossible for one entity (not talking about a mining pool here) to get half the network hashrate. Still - there are scenarios where 51% attacks are possible.