We hear a lot about the 51% attack, but what is it really about?
The 51% attack is a hacking procedure that is perpetrated against the blockchain in order to take over the ability to validate or cancel transactions at will.
Basically it consists in the possibility that miners or pools of miners have to reach half + 1 of the computing power of the entire network.
Once obtained this possibility the pool at 51% can decide to address the blockchain as it likes.
Obviously it will address it in order to seize as many coins as possible.
With this procedure you cancel all the security created to avoid double spending.
Beware, however, in this way the attackers can "only" manipulate the functioning of the blockchain!
Clearly, talking about computing power, we are talking about all those blockchains that use a PoW consensus.
Once the crooks have managed to get 51% they can start performing disruptive procedures by slowing down the consensus rate, validating, later on the transaction to their advantage.
They basically rewrite the blockchain incorrectly but having the ability to validate the transactions as correct, no one can stop them.
On top of that, being a PoW validation, they are also rewarded for writing illegitimate and incorrect things.
At this point you will ask yourself a question: then with the 51% attack you can change the supply of the various coins?
No, absolutely not.
With the 51% attack, you take over the global computing power for validation, you don't enter the code that has been written for the definition of the bad coin.
As soon as the 51% attack is launched, you can tell right away: the blockchain practically crashes: the miscreants have to slow down the validation of transactions by a lot in order to then take over the other miners.
Attack on 51% and 34%
Just as the 51% attack exists in the type of blockchain with PoW and PoS validation, the 34% attack exists in blockchains that use the Tangle validation method (IOTA for example).
The substantial difference between the two attacks has consequences arising directly from the difference in validation of the two types of blockchain.
As we know with PoW you only validate and write a block when you have solved the problem proposed by the network; so with the 51% attack in a PoW blockchain, you gain total control of the network.
Do you remember how Tangle works?
No problem, I'll remind you immediately: confirmation using Tangle is done by taking the validation of a previous block (possibly the furthest away from the transaction to be validated) and you validate 2 subsequent transactions.
As you can logically understand, if you launch a 34% attack on a Tangle you can only validate or cancel transactions, you cannot take full control of the blockchain!
The safest way to avoid the 51% attack is to change the validation method from PoW to PoS: in order to manipulate the network you would need a very high amount of funds to be placed in staking, which by the platforms are restricted on purpose.
Obviously all blockchains are subject to this kind of attack, but just think for a moment the computing power that would be needed to be able to take over the Bitcoin network: too high a figure to have a tangible result.
That's why the blockchains targeted are the smaller ones.
Also to ward off this possibility, Ethereum is upgrading to ETH 2.0, where block confirmation will be done through the use of PoS .
Obviously, the 51% attack still remains a demon creeping into the cryptocurrency world, but the technology is well aware of it and is already moving to prevent it from recurring.
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