41
votes
51% attack - apparently very easy? refering to CZ's "rollback btc chain" - How to make sure such corruptible scenario can never happen so easily?
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 ...
- 110k
27
votes
Accepted
Why do we call it a 51% attack instead of a 50% attack?
The distinction is of theoretical importance only. But if the attacker controls exactly 50%, then it's true that the attacker will eventually catch up, but he won't stay caught up: the honest ...
- 23.1k
25
votes
Why does Bitcoin no longer have checkpoints?
The issue is that you assume a majority attack is an attack that can be prevented. It is not. It is a fundamental breakdown of the security assumptions.
Proof of work (PoW)'s assumption is that the ...
- 110k
10
votes
51% attack and rewriting to the latest checkpoint
As long as both competing chain-tips are adhering to the same rules, the chain with the most aggregate difficulty ("heavier") will win, regardless of height. Nodes performing the initial sync would ...
- 77.9k
10
votes
51% attack - apparently very easy? refering to CZ's "rollback btc chain" - How to make sure such corruptible scenario can never happen so easily?
(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 ...
- 7,727
9
votes
Accepted
How does the network protect itself against attacks where one miner with a lot of hashing power lies that it takes 10 minutes to create a block?
What you describe is a (variant of a) majority attack: if an attacker can construct a block every 3 minutes while the rest of the network can only construct a block every 10 minutes, that means the ...
- 110k
7
votes
Why don't the miners just take profit from our coins and make the coin worthless?
Because miners do not actually own/ or have access to the bitcoins which are being spent in a transaction.
They simply choose a number of transactions which have valid signatures, and put them ...
- 1,081
6
votes
Why do we call it a 51% attack instead of a 50% attack?
This is to impart the need for a higher hash rate than the rest of the (honest) miners. Mining success is probabilistic, however, so this 50% or 51% is an indication of the expected behaviour given an ...
- 786
6
votes
Accepted
Couldn't Microsoft execute 51% attack?
Microsoft's software runs on a very large number of PCs. However the computers in question generally don't have specialised hashing hardware - they only have typical central processing units (CPUs) ...
- 28.5k
5
votes
Accepted
51% attack clarification
Yes, the attacker needs to be faster than the rest of the network combined. Being faster than the second-fastest miner is not enough.
I think this is where you are mistaken:
Blocks in the ...
- 8,852
5
votes
Is "fee higher than block reward" attack possible?
An attack like this is possible, it is just a way to profit off a 51% attack. However you must remember several things:
if a miner controls less than 51% of the hashpower, then chances are they will ...
- 18.4k
5
votes
Why has BCH not received a 51% attack yet?
Because of the cost, specifically the opportunity cost.
If a miner has 10% of the BTC hashrate, then if they pointed all of that mining power to BCH, they would still be losing money. With 50% of the ...
- 72.2k
5
votes
Accepted
Can a bitcoin transaction from a specific bitcoin address be banned? (via mining pools)
Yes, miners can censor transactions. A mining pool (or solo miner) can choose to not add a transaction to any blocks that they create. And, of course, this can be done dynamically so that transactions ...
- 72.2k
4
votes
Why wouldn't miners change the protocol? (e.g. change difficulty)
The rest of the network, which uses the existing difficulty parameters, will reject the new blocks generated by your modified miners. There will be a longer blockchain, but there will not be a longer ...
- 3,431
4
votes
Accepted
How exactly are Bitcoin's consensus rules enforced?
But how exactly the consensus rules are forced?
Every single full node enforces them.
Internet says that the consensus rules are the rules thet every full node follows. And rejects blocks that do ...
- 51.7k
4
votes
51% attack - apparently very easy? refering to CZ's "rollback btc chain" - How to make sure such corruptible scenario can never happen so easily?
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 ...
- 18.4k
4
votes
Don't miners control who is allowed to make transactions?
The stakeholders of bitcoin don't want miners to do that. If miners do that, the stakeholders (the people who are paying for the miners to mine) would change the rules. For example, they'd change the ...
- 51.7k
4
votes
Accepted
Can a 51% attacker earn mining rewards on the blocks they tampered with?
When the attacker broadcasts the chain they had been working on in private, will they get mining rewards for all those new blocks after the reorg?
Yes, the majority attacker can create the longest ...
- 18.4k
4
votes
Can someone with majority hashing power decide what transactions are included in my block?
If I somehow was able to mine a block, How can someone with majority hashing power can decide transactions to include in my block
Nobody else can influence the contents of the block you are working ...
- 18.4k
4
votes
Attack the network by having 51% of full nodes?
The question has the appearance of mixing up two different types of attack
The so-called "51% attack"
The "eclipse attack"
The first is where an attacker controls >50% of the ...
- 28.5k
4
votes
Accepted
Can the two biggest bitcoin mining pools lock out all others?
It's certainly not an ideal situation. However them cooperating to censor outsiders' blocks doesn't make it impossible for anyone else to "squeeze in a block" ever again. In order to prevent ...
- 9,146
4
votes
Accepted
How can an external party be sure that node's response is valid?
A Merkle inclusion proof is a proof that a transaction is included in a block with a particular hash, nothing more. Whoever gave you that proof can lie by omission (claiming no transactions you asked ...
- 110k
3
votes
What is "If ghash.io hits 51% people would just leave them?" referring to?
GHash.io was a big mining pool back when mining pools were mostly just a way to organize for large numbers of small private mining operations. (Whereas today, the biggest mining pools own huge mining ...
- 77.9k
3
votes
What is "If ghash.io hits 51% people would just leave them?" referring to?
No, the network wouldn't disconnect them. There's no way for that to happen.
Recall that a pool is an association of miners who agree to share the proceeds of their mining; whenever anyone mines a ...
- 23.1k
3
votes
Accepted
How to extract maximum value from a 51% attack
If an attacker were to gain 51% of the network, they can essentially forge arbitrary transactions.
With control over a majority of hash rate (either directly, or by using something like selfish ...
- 12.2k
3
votes
Accepted
Is possible to destroy the Bitcoin for just $500K? (51% attack)
TL/DR: No.
The long form of the answer:
Online mining is that grey area where you don't invest until you're 100% sure. The aforementioned website is likely to scam you if they are providing such a ...
- 520
3
votes
Why can a 51% attacker not change the block reward?
Even you have 51% of hashpower you can not change the software on other computers to accept your blocks.
- 6,835
3
votes
Why would more confirmations help in a 51% attack scenario?
If the exchange waits for 6 confirmations (1 hour) and sends the dollars then, it could be possible that no one even noticed that there was such an attack. Then a scammer could pay out twice.
But if ...
- 2,127
3
votes
Do you really need more than 50% mining power in order to attack Bitcoin blockchain?
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 ...
- 18.4k
3
votes
51% attack - apparently very easy? refering to CZ's "rollback btc chain" - How to make sure such corruptible scenario can never happen so easily?
There a are a few things to take into account when we consider the probabilities of a rollback attack (a posteriori reorg destroying net value) to be successful:
If the reorg is shallower than 100 ...
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