Cryptopedia
Sybil Attack
The book “Sybil” is about the treatment of Sybil Dorsett for multiple personality disorder. Named after the book, Sybil attack is a type of attack commonly seen in networks in which the attacker creates a large number of pseudonymous identities. With these identities, click farming can be achieved by hackers. The easy targets of Sybil attacks are redundancy mechanisms, which create multiple copies of files across several hard drives for greater network security, such as the blockchain technology. As a result, with distributed data storage, a blockchain is vulnerable to Sybil attacks.
How to Launch a Sybil Attack:
To launch a Sybil attack, a hacker needs to use a physical node to forge multiple identities (known as Sybil nodes) and broadcast these fake identities to the whole blockchain network. Sybil attackers can use these identities to communicate with honest nodes. In this way, these nodes will receive no response or be misled. Moreover, in a blockchain network, attackers may be able to out-vote the honest nodes on the network if they create enough fake identities. They can then refuse to receive or transmit blocks, effectively blocking other users from a network, in order to dominate the blockchain network. After dominating the network, they are able to tamper with transaction data and change the chronological record of transactions, which will impose a great threat to the network.
The Prevention of Sybil Attacks:
Sybil attacks are ineffective for public blockchains which are based on consensus mechanisms, with an unknown number of nodes. These blockchains don’t rely on the number of nodes for data verification. For instance, Bitcoin prevents Sybil attacks via the proof-of-work algorithm, requiring nodes to carry out tremendous computation to be legitimate. Only the legitimate nodes can alter the data in a block. In this sense, launching an attack is more costly than being an honest node for Sybil attackers. On the other hand, run by a group of pre-defined nodes, consortium blockchains are often attacked by Sybil attacks as the number of nodes is known to every node. At present, these blockchains rely on identity verification when attacks happen, which can block Sybil nodes. There are two ways to verify the identity of a node, including the verification by a third-party institution and the endorsement of the authorized nodes.
How to Launch a Sybil Attack:
To launch a Sybil attack, a hacker needs to use a physical node to forge multiple identities (known as Sybil nodes) and broadcast these fake identities to the whole blockchain network. Sybil attackers can use these identities to communicate with honest nodes. In this way, these nodes will receive no response or be misled. Moreover, in a blockchain network, attackers may be able to out-vote the honest nodes on the network if they create enough fake identities. They can then refuse to receive or transmit blocks, effectively blocking other users from a network, in order to dominate the blockchain network. After dominating the network, they are able to tamper with transaction data and change the chronological record of transactions, which will impose a great threat to the network.
The Prevention of Sybil Attacks:
Sybil attacks are ineffective for public blockchains which are based on consensus mechanisms, with an unknown number of nodes. These blockchains don’t rely on the number of nodes for data verification. For instance, Bitcoin prevents Sybil attacks via the proof-of-work algorithm, requiring nodes to carry out tremendous computation to be legitimate. Only the legitimate nodes can alter the data in a block. In this sense, launching an attack is more costly than being an honest node for Sybil attackers. On the other hand, run by a group of pre-defined nodes, consortium blockchains are often attacked by Sybil attacks as the number of nodes is known to every node. At present, these blockchains rely on identity verification when attacks happen, which can block Sybil nodes. There are two ways to verify the identity of a node, including the verification by a third-party institution and the endorsement of the authorized nodes.
