Bitcoin Forum

I saw an article about Sybil attack on Blockchain and Cryptocurrencies and some of its (Sybil attack) impacts were really threatening to both security and privacy.
So I thought if it was really possible for some like that to be pulled off?

copied the quoted words from: https://academy.bit2me.com/en/que-es-un-ataque-sybil/

Yes it was possible if someone modified the node which be able to collect the information of the users like IP connected to the nodes that is why using the TOR gives the extremely high privacy if you're really concerned about it. But normally nodes doesn't store the IP address apart from core used to download the blockchain and it never stores the transaction details we make in future.

This could easily be mitigated by using Bitcoin nodes together with Tor network, so the real IP addresses won't be exposed.
Sybil attack can still happen on Tor network exposing some data, but it's highly unlikely this would cause any serious takeover of Bitcoin network.
Privacy could still be compromised and I don't know how we could prevent this in bitcoin blcokchain.

Actually Sybil attack is about "gaining large influence in a network". For example you could create a lot of identities in a network using different Email addresses and user names. But in Bitcoin, this "influence" is basically translated into hashrate ergo the way Proof of Work is defined prevents that already because you can't magically summon computing power to gain a significant amount of influence on the network.

My understanding is that the meaning of "Sybil Attack" is more specific than what you are describing. It is a way to get around a per-identity limitation by creating multiple identities.

As far as I know, there are no explicit per-identity limitations in Bitcoin, so I don't think Bitcoin is vulnerable to any kind of Sybil attack.

The idea of creating a large number of nodes to control the information sent to other nodes is called an "Eclipse attack".

Here is an example of a hypothetical Sybil attack against Bitcoin. Many people have naively suggested that to prevent any one miner from getting more than 51% of the hash rate, we would simply limit the miner's contributions. The obvious evasion is a Sybil attack. The miner would to split their identity into multiple separate identities who all belong to the same miner. The individual identities would be limited, but the miner would not.

There are plenty of examples of Sybil attacks outside of Bitcoin and cryptography. Creating fake voters to influence the outcome of an election is a Sybil attack. Creating fake users to boost product reviews and reputation scores are Sybil attacks.

Sybil attack is possible in Bitcoin but for that to happen is to gain control of several node which is what is stated in previous post "gaining large influence in network" then it would happen but for now, I don't think there's someone or a group who have gained what is needed for sybil attack to happen. If that is not possible then this wouldn't have been discussed before and other attacks on cryptocurrency.