51% Attack: All That You Need to Know


As far as the blockchain world is concerned,  a network’s mining or computing power or hash rate is controlled more than 50% by a miner or a group of miners. This is precisely what is known as A 51% attack.  In this blog, we are trying to understand how the attack on blockchain functions. Miners, by attacking a blockchain can block various transactions from being confirmed or becoming successful.

Photo by Sora Shimazaki from Pexels

What is a 51% attack? 

Most 51% of attacks in a blockchain happen to reverse transactions which are called double-spend. These attacks happen on Bitcoins that have already been spent. Let us try to understand this with the help of an example:

10 bitcoins can be spent to purchase a car. Once the car is delivered the bitcoins are to be transferred to the seller. This transaction can activate the attack. In case of a 51% attack, the transaction can be reversed which will result in a refund of the 10 coins used. Thus the person will have no investment behind the car as he will receive back the number of bitcoins he has invested.

To know more, check out android wallets! In the following section of the blog, we will quickly have a look at how a 51% attack occurs.

How does a 51% attack happen?

When a transaction or purchase happens using Bitcoin it goes into a pool of transactions that are not yet confirmed. While bringing out the POW, the miners untangle the block of transactions and clear out the unconfirmed transactions. This process is called mining. The miner must solve a puzzle in order to put a transaction into a blockchain. 

The puzzle is usually a very complicated mathematical puzzle which has to be done with enhanced computational power. The chance of a miner successfully putting a block to a blockchain depends on the computational power and intelligence of the miner. Furthermore, the right answer to the mathematical problem can be broadcasted in the network. There however are certain miners who refrain from broadcasting solutions out in the network. 

As a result of this situation, two different versions of the block chain are created. One of the blockchains is the original block chain which is followed by honest miners who are mining and the other blockchain consists of blocks whose results are not broadcasted in the network. The dishonest miner mostly continues to work in the duplicate version of the blockchain and can spend his bitcoins on the original version of the blockchain that the honest miners are following. 

Things to Remember:

  • Democratic Governance: A minor must have Extraordinary computing or hashing skills in order to successfully add blocks to a chain. A block chain is designed in a way which follows the longest chain and it is always considered as the purest and most legit block chain. A good miner should keep adding blocks to the network faster, which results in informing the longest block chain which is then going to be considered legitimate. 
  • Duplicate Chain: A dishonest miner will keep on adding blocks to the duplicate chain that he has created at a faster rate so that it is considered as an honest chain. Once it becomes the longest chain the  corrupted minor would broadcast it to the network in order to initiate the 51% attack process. The original blockchain would cease to exist once the dishonest network is being detected and the whole process will be shifted to the new corrupted one. 
  • Transaction Reversal: Since the dishonest blockchain is now considered as the legitimate blockchain the transactions that happened are reversed. All the bitcoins spent are now refunded as the original transactions are now considered illegitimate. This phenomenon is called the double spend.
  • The probability of 51% attack: One needs to have extravagant intelligence and capability in the world of hashing power or computing power to create a duplicate network of blockchain and thus 51% of attacks are now a rare sight. What are the odds against millions of super talented miners, who mastered the art of solving high-end puzzles for mining Bitcoins? 


We hope this blog tells you all about the 51% attack and things you should know about it. Further, we wish you luck with your future endeavours in this realm!


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