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Sybil Attacks – What are They and How Do They Affect Blockchains?

  • Sybil attacks- A security threat to blockchain systems.
  • The attacker creates multiple identities or nodes in blockchains simultaneously.

The world has seen a far greater adoption of blockchains than expected, and the main reason behind this can be the decentralized nature and the security they promise. However, when it comes to security, it seems technology has some shortcomings in it. Such a notable example of a shortcoming is the Sybil Attack. 

Sybil Attacks- What are They?

A Sybil attack violates the security of blockchain systems by creating multiple fake identities simultaneously. Most importantly, all these fake identities are operated by a single node. The attack is done with the purpose of gaining maximum authority to influence the whole blockchain system. On achieving the major influence, it will become easier for the attacker to perform unauthorized actions in the network.

The attack gained its name from a novel written by Flora Schreiber in 1973. The book has a woman character called “Sybil”, who is diagnosed with a disease named Dissociative Identity Disorder. In this disorder, a person has multiple identities. However, the term rolled out in tech when John R. Decor released a short research paper titled ‘The Sybil Attack”.

How do they affect the blockchains?

This type of attack causes a huge impact in the functioning of blockchains and makes it difficult to operate. So, it is important to know what they can cause to blockchains.

  • First, the attackers can gain a majority and can carry out a 51% attack. A 51% attack is a malicious activity in which one single node or company manages the entire network of blockchain. In such a case, the attacker can change the order of transactions, and also prevent the transactions from being confirmed. It can also lead to double spending.
  • Second, the attacker can withhold the transaction and refuse to add new blocks to the chain. This will lead to it becoming stagnant and thus, also allowing the entire blockchain to get disrupted.
  • Third, it can cost you a huge amount of privacy. It can collect the sensitive details of the honest nodes by running a malicious node. It can also obtain the IP addresses of the honest nodes.
  • Last but not the least, if this attack happens in the blockchain of any cryptocurrency, then the hacker can redirect the currency in his unauthorized wallet, causing a huge loss. 

How to Prevent Sybil Attacks?

Such attacks can be disastrous for the authenticity of the whole blockchain network. Thus, Blockchains take into consideration various ways to mitigate the risk of Sybil attacks. Some of them are:

  • Blockhains integrate various consensus mechanisms such as Proof of Work (PoW) and Proof of Stake (PoS). These mechanisms make it difficult for one to achieve the majority as they require a huge amount of energy and money to validate the node. 
  • Blockchains can also differentiate or segregate the node based on the level of trust. It can give importance to nodes who are validating the process for a long time. While to the new nodes, it gives less importance. 
  • Last but not the least, blockchain can use custom defense mechanisms which have inherent protection against sybil attacks. The examples of such technology are Kademlia, SumUp, and Whanau.


To end with, Sybil attacks can cost a huge impact on blockchains by creating multiple fake identities operated by a single entity. The main purpose of these attacks is to get major influence on the network. However, they can always be prevented by a bunch of measures, but it is hard to implement such types of attacks as it requires a huge amount of energy and cost.

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