Technology has revolutionized the way people interact in all areas of life. However, these upgrades don’t come without risk. While blockchain specifically may have provided a more secure, transparent means for transactions in general, the risk of an attack remains. One of the leading threats in blockchain technology today is known as a Sybil attack. It’s an online security attack where multiple fake identities are controlled by one computer. However, Sybil attack prevention is possible.
In this guide, we go over the different types of Sybil attacks along with the problems they cause on an online network. We also go over the ways in which you can prevent them. This way, you can use online networks with more confidence and trust.
What is a Sybil attack?
A Sybil attack is an online security threat in which one computer — referred to as a node — operates multiple fake identities on a peer-to-peer (P2P) network. Similar to when someone creates multiple social media accounts, one single user can run multiple nodes (IP addresses or user accounts) simultaneously on the network.
The attack name was inspired by a character in Flora Rheta Schreiber’s 1973 book “Sybil” named Sybil Dorsett.
In Schreiber’s book, Sybil was treated for Dissociative Identity Disorder — or Multiple Personality Disorder. This disorder is characterized by one person exhibiting several distinct personalities, much like how the attack is done on a peer-to-peer network. However, the term Sybil was actually coined by computer scientist Brian Zill and discussed in John R. Douceur’s paper.
How does a Sybil attack take place?
Sybil attacks take place when a single entity (node) impersonates real users on a network they wish to infiltrate by creating multiple accounts. Each new identity acts independently from the other and performs its own transactions. It appears as if each node is operated by its own individual entity when in reality, it’s one person controlling them all.
Sybil attacks are not limited to just blockchains. However, because blockchain networks are governed by majority influence, a large-scale Sybil attack risk is high since it gives the attacker more centralized authority on a decentralized platform.
This can happen on networks such as Bitcoin because many decisions depend on a majority vote. With this much control over the system, an attacker can rewrite the distributed public ledger. Likewise, a Sybil attack on social media can influence the majority opinion since many of the users are being manipulated by one person.
Types of Sybil attacks
To better understand how Sybil attacks work, it would help to know the different types of Sybil attacks that exist. Both malicious and authentic nodes run on the same network, but how they communicate is classified into two categories: direct and indirect.
In a direct attack, honest nodes on the network are directly influenced by the Sybil nodes. The malicious nodes communicate with authentic nodes while simultaneously mimicking an honest node. The real nodes don’t realize they are being duped. As a reason, they readily accept influence from the fake ones and allow direct communication.
In contrast to a direct attack, indirect attacks involve another set of nodes that act as middlemen. These unsuspecting nodes are actually under the influence of the Sybil nodes, so they remain compromised. Therefore, the communication between the Sybil nodes and the honest nodes is indirect; they don’t interact with each other. These types of attacks allow Sybil nodes to run a network more undetected than in a direct attack.
Problems caused by Sybil attacks
The goal of a Sybil attack is to gain influence over an entire network to control decisions that are made. A successful attack can create problems, including:
- Setting up a 51% Attack: A 51% attack on a blockchain network is characterized by control of over half of the network’s computer power — referred to as a hash rate. This can potentially cause a network disruption since transactions can be modified by majority power. In a 51% attack, an attacker can create fraudulent transaction blocks while invalidating others. In addition, with this much control, they can also enable double-spending by reversing transactions.
- Blocking users from a network: When enough false nodes are set up on a network, the attacker can essentially vote out honest nodes. This also enables the Sybil node to refuse either transmitting or receiving blocks. As a result, honest nodes are unable to access the system.
How to prevent a Sybil attack
For years, computer scientists have put in a lot of effort to find ways in which Sybil attacks can be prevented. As of now, there is no one way to guarantee defense against an attack fully, but there are some steps that can be implemented to maximize security and prevention.
Blockchains are secured by the type of consensus algorithm they use. A consensus algorithm describes the process in which agreement regarding the transactions is established on a blockchain. In the case of proof-of-work, the process of mining is done when miners (nodes) on the network use up computing power to solve complex mathematical problems to verify transactions.
Therefore, to reach a collaborative consensus on the blockchain, enough miners need to agree on the authenticity of the data. This process makes it almost nearly impossible for one entity to gain control of more than half of the network when there are so many miners needed to verify. In addition, it would be very costly for one person to own the majority of the equipment since each node is represented by one single computer.
Depending on the network, there are multiple ways in which ID verification can be done, either directly or indirectly. Through direct validation, a central authority verifies the new identities. When validation is done indirectly, established members who have already been verified can then verify the new identities. These procedures often require new members to identify themselves via credit cards, IP addresses, or two-factor authentication.
Another way to ensure ID verification is to require a fee for every identity that is created which will make it extremely costly for one entity to acquire so many nodes.
A reputation system gives power in varying degrees to the members of the network. These power levels are based on the reputation level of the member. Generally, those who have been in the system for a longer period are given more power to perform tasks or more interactions.
These members have built trust over time and have proven to be honest nodes, so they can exert more power over Sybil nodes and override them. This type of power in a system often discourages attacks from happening since attackers would have to wait a long time to reach higher reputation levels.
Are all blockchains vulnerable to Sybil attacks?
Theoretically, all blockchains are vulnerable to Sybil attacks. However, the size of the network does often make a difference. The more miners needed to validate transactions, the better, since it’s extremely difficult for one entity to control 51% of the miners. Due to Bitcoin’s large network, for example, it has proven to be more resistant against both Sybil and 51% attacks. No one has ever been able to successfully perform a 51% attack on Bitcoin.
Sybil attacks are something to be concerned about, but for the most part, teams need only take a few precautions to prevent it from happening. As always, security decisions in the design process are a priority in the development process.
Frequently asked questions
A Sybil attack is a malicious security threat that takes place on a peer-to-peer network in which one computer operates multiple fake identities. The goal behind these types of attacks is to gain an unfair advantage and control over other users on the network.
Most blockchain networks are vulnerable to Sybil attacks. However, in the case of Bitcoin, it is practically impossible because of how many miners there are.
Sybil attack prevention is possible through consensus protocols, identity verification, and having enough nodes on the network. In the case of identity verification, validation on the network can be done directly or indirectly.
Consensus algorithms such as proof-of-work or proof-of-stake are used to defend against Sybil attacks on a blockchain network. These algorithms help prove the authenticity of transactions and provide incentives to nodes for honest work, thereby limiting the desire to act dishonestly.
A Sybil attack in IoT is when one node generates or steals the identities of other nodes on the network to compromise the system or to diffuse spam.
A 51% attack on a cryptocurrency blockchain occurs when a group of miners controls more than 50% of the mining hash rate on a network. Because the miners own at least 51% of the blockchain, they have the power to alter the network.
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