LBlockchain technology since its inception has had a weakness by design that its developers seek to avoid, it is called 51% attack. This attack allows one or more malicious agents that control at least 51% of the network to do what they want with it. There are no limits to the actions they can take on the blockchain. They are majority and as such they can rewrite or even perform a DoS attack on the network.
This weakness is related to the way in which blockchain networks are structured. These are but a series of nodes distributed. All of them driving a consensus protocol It is based on the trust and work offered by a majority group of participants. This is to avoid that the existence of a low percentage of malicious nodes can create chaos on the network.
However, the story completely changes when malicious actors come to have 51% or more of the network's power. At this point, as we have said before, they can do whatever they want. From there derives the name of the attack, because that percentage of power is the minimum necessary to carry it out.
How are these attacks carried out?
Performing a 51% attack is not technically complex. It is enough to have a mining node and have the majority participation in the blockchain network. That is all that is really needed, and this situation might sound worrisome, but it is not. Well, the problem lies in having that majority participation. A situation that depending on the blockchain can cost a few thousand dollars or cost millions.
Take for example the case of Bitcoin. With its consensus protocol PoW and algorithm SHA-256 It is technically quite easy to make such an attack. There are powerful machines ASIC y FPGA that can facilitate the task of obtaining computing power. However, the size and total distributed computing power of the Bitcoin network make the attack difficult. It would not take thousands of these teams to successfully carry out our attack. A situation that would raise costs to millions of dollars. An economic expense that might not be rewarded for the profits that the malicious actor could obtain for his successful attack.
But if instead of Bitcoin we take a smaller blockchain like LeaCoin, the story changes. With the same consensus protocol and Bitcoin hash function, LeaCoin It is a small and easily attachable blockchain. With a total computing power that barely exceeds 1 TH / s, a current ASIC team would be enough and more than enough to carry out this attack. If the attacker could take financial advantage of the situation, he would undoubtedly be a prime target. The reality is that LeaCoin has very little value and is considered a shitcoin.
The history of these attacks is repeated over algorithms like PoS y DPoS, each of them with their difficulties and particularities.