A Sybil attack is a type of threat to an online system where a person attempts to take control of the network by creating multiple accounts, nodes or computing power.
This could be as simple as a person creating several social media accounts. But in the world of cryptocurrencies, a more relevant example is when someone runs several nodes in a Blockchain network.
The word “Sybil” originates from a book called Sybil. The book is a case study about a woman named Sybil Dorsett, who had been diagnosed with Dissociative Identity Disorder - DID.
What problems can a Sybil attack cause?
Attackers can have a majority in a network if they are able to create false identities (nodes) in greater numbers than true identities. They would then be able to refuse to receive or transmit the blocks, effectively blocking other users of the network.
In large-scale Sybil attacks, where an attacker is able to control the majority of the network's computing power or hash rate, it is possible to execute a 51% attack. In these cases, they may be able to modify the order of transactions and prevent transactions from being committed. They may even be able to reverse transactions they made while in control of the network, this could lead to double spending.
Over the years, computer scientists have devoted a lot of time and research to understanding how to detect and prevent Sybil-type attacks, with varying degrees of effectiveness. For now, there are no guarantees of defense.
How blockchains can prevent Sybil attacks
Blockchains use different types of consensus algorithms to help defend against Sybil attacks. The main ones are: Proof of Work (PoW), Proof of Stake (PoS), and Delegated Proof of Stake (DPoS).
These consensus algorithms do not prevent against a Sybil attack. They just make an attack like that pretty impractical.
For example, the Bitcoin Blockchain uses a series of specific rules to create a new block.
One of these rules is that the ability to create a new block must be proportional to the total processing power of the Proof of Work engine. This means that you actually need to have the processing power necessary to create a new block, which makes this difficult and costly for the attacker.
Because Bitcoin mining is so intense, miners have a strong incentive to keep mining honestly rather than attempting a Sybil attack.
In addition to Sybil attacks, there are other types of cyberattacks. Stay tuned to Binance Academy to learn more!