What Is Sybil Attack?

What Is Sybil Attack?


The online network can be vulnerable to a security threat known as a Sybil attack. This occurs when an individual attempts to dominate the network by creating numerous accounts, nodes, or computers. Multiple social media accounts can be created by one individual, for instance. However, in the domain of cryptocurrencies, the attack involves one person operating multiple nodes on a blockchain network. The attack is named after Sybil Dorsett, who was a case study subject and underwent therapy for a psychological condition referred to as Dissociative Identity Disorder or Multiple Personality Disorder.

Problems Caused by Sybil Attacks

If an attacker creates enough fake or Sybil identities, they could potentially out-vote the honest nodes on the network, rendering it ineffective for other users. They can do this by refusing to receive or transmit blocks. With large-scale Sybil attacks, where the attackers control the majority of the network computing power or hash rate, they may conduct a 51% attack. During these attacks, they can change transaction order, block confirmation, and reverse their own transactions, leading to double spending.

Despite years of research and dedicated efforts by computer scientists to detect and prevent Sybil attacks, there is currently no guaranteed defense. The effectiveness of their various approaches varies.

How Does Blockchain Help With Sybil Attacks?

To counter Sybil attacks, numerous blockchains implement distinct "consensus algorithms," such as Proof of Work, Proof of Stake, and Delegated Proof of Stake. However, these algorithms don't stop Sybil attacks; they only make it exceedingly impractical for an attacker to conduct a Sybil attack.

For instance, the Bitcoin blockchain has specific regulations for creating new blocks, one of which stipulates that the ability to generate a block must be commensurate with the overall processing power of the Proof of Work mechanism. This implies that an individual must have enough computer power to create a new block, which makes it both difficult and expensive for an attacker to do so. Because Bitcoin mining is so laborious, miners have a strong motivation to maintain honest mining practices instead of trying to conduct a Sybil attack.


Sybil attacks can be a serious threat to online networks, including blockchain systems. While there is no guaranteed way to prevent these attacks, consensus algorithms like Proof of Work make it difficult and expensive for attackers to dominate the network. The ongoing effort by computer scientists to detect and prevent Sybil attacks is crucial in ensuring the integrity and security of these networks.

Sybil Attack
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