35

Disclaimer: I believe this question may be primarily opinion-based and not very appropriate for this site, but there are a number of technical misunderstandings that can be clarified along with it, so I'll give it a shot. There are many nuances involved here, and I fear that a large part of them didn't reach as much of an audience as the exchange announcing ...


9

(adding some color) Some discussion I saw suggested that people promoting this believed they only needed to achieve >50% hashpower, which caused them to overestimate the feasibility. Reorging with only slightly over 50% would take weeks-- even months, creating massive disruption if successful, and virtually guaranteeing an effective public initiative to ...


4

I want to add a little bit to the coordination problem that @PiererWuille mentioned. Not only does the probabilistic success of a rollback depend on the ability of miners and affected parties to coordinate, it also requires that individual miners must trust one another to participate in the rollback. Consider this: If I had a significant portion of the ...


3

A majority attack (51% attack) was given this name for a reason: in order for the attack to succeed on average, the attacker needs 51% of the hashpower. Reading your question, I can see a misunderstanding of how mining works, in that you postulate two miners working together with 40% of the hashpower will outcompete 3 miners with 20% of the hashpower each (...


2

There a are a few things to take into account when we consider the probabilities of a reorg attack (destroying net value) to be successful: If the reorg is shallower than 100 blocks (COINBASE_MATURITY), the attacker can minimize the amount of direct victims. But if we are talking about a deeper one, not only the payments he wants to revert may have been ...


2

I believe you are asking if the inter-block interval matters for the success rate of a high hashpower reorg attack. It does, because if it is too fast the honest participants will spend a substantial fraction of their time not working on the same (honest) chain, because they haven't heard of each others blocks or have created their own blocks before other ...


1

One may speculate on this, but this was already taken into account in the design of Bitcoin. Essentially an attacker would not choose to attack the network because it would hurt their own investment. In the whitepaper, Satoshi states: if a greedy attacker is able to assemble more CPU power than all the honest nodes, he would have to choose between using ...


1

No, each node (assuming that it is a miner) can pick a different set of transactions. Eventually one block will get more work built on top of it than all the others and the other competing blocks at the same height in the chain will become stale and be discontinued. Effectively the blockchain forks but eventually one branch survives and the others die. ...


1

Yes. The owner of 51% can get 100%. This is attack-51 itself. Is there some measure that would stop this? no


1

This question is somewhat like asking, "how can I steal money from myself?" Since you are the only person participating in the consensus of your altcoin, you control 100% of the hashpower. A 51% attack creates an alternative ledger, breaking consensus on which coins have been transferred, allowing the attacker to create a double spend. First mine two ...


1

Your answer is Incentives. Let's imagine a bad guy, called Mallory, has an interest in attacking Bitcoin and has either created for himself, or desires to, 51% of the hashing power required to start shenanigans. (Start, because he has to maintain and grow that hashing power for sufficiently long to outpace the 'good guys'.) To start with, there's no ...


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