Sybil resistance refers to the ability of a [[Consensus Mechanism|consensus mechanism]] to prevent or mitigate attacks from malicious actors creating multiple fake identities, known as Sybils. A Sybil attack occurs when an adversary creates multiple fake identities to gain control of a majority of nodes or computing power, enabling them to manipulate transactions or disrupt normal operations. For this reason, Sybil resistance is critical to blockchain because it ensures that participants in the network have proportionate voting power on [[Finality|finality]]. In the case of Bitcoin, which uses [[Proof of Work]] as its consensus mechanism, a Sybil attack would involve an attacker attempting to control more than 50% of the total mining power on the network. By doing so, they can perform [[Double-spending|double-spending]] attacks, or halt transaction confirmations, ultimately splitting into a competing chain. This is more widely known as a [[51% Attack]]. To improve resistance to spammy transactions at a smaller scale, functions like [[Opcodes|opcodes]] allowed for some battle-testing of Bitcoin's finality.