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Sybil Attack Meaning

Sep 8, 2023 | Updated Sep 8, 2023
A Sybil attack is a security threat on a peer-to-peer network where a malicious actor attempts to sabotage the network’s reputation by creating multiple fake identities.

What is a Sybil Attack?

A Sybil attack, or “pseudospoofing”,  is a type of cyber attack that undermines a network’s reputation. It involves a single computer – known as a node – in a peer-to-peer (P2P) network attempting to operate multiple fake identities (Sybils or  “sock puppets”) simultaneously to gain control over the network. In a blockchain network, the Sybils could work together to prevent transaction confirmation, launch a double-spend attack, or disrupt the network’s overall functioning. 

Sybil attacks are similar to fraudulent voting in an election. A person creates multiple accounts and then casts fake votes across different options to demonstrate an illusion of mass support for a certain choice. By casting lots of votes from the Sybil accounts, a user can manipulate the network and undermine the integrity of the system.

What Problems Can Sybil Attacks Cause?

A Sybil attacker can launch a mining attack on a blockchain network, where the malicious actor uses the Sybils to mine blocks faster than every other miner. As a result, the actor would receive an undue share of the block rewards and undermine the blockchain’s security.

If the entity creates a significant amount of Sybils to control over 50% of the network nodes, it could launch a 51% attack. In such a case, the attacker can prevent transaction confirmation, double-spend coins, change the order of transactions, and censor specific blocks. They can also dictate which changes the protocol accepts and manipulate the network’s consensus rules.

In a different scenario, a Sybil attack can disrupt a network by overwhelming it with fake transactions. The entity floods the network with bogus transactions to create congestion, which makes it difficult for the network to process genuine transactions.

Blockchain networks use consensus algorithms such as proof-of-work (PoW) and proof-of-stake (PoS) to make it difficult to execute Sybil attacks. PoS networks require nodes to stake a specific amount of cryptocurrency to participate in the consensus process. It ensures that users can’t create enough Sybils to control the network’s hash power. 

In PoW networks, block creation is directly proportional to the total processing power. This means that to create a new block, the Sybil attacker must possess the actual computational power. Sybil attacks in PoW networks are highly unlikely since garnering such computational power is costly and extremely difficult. 

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