Sybil resistance

The core idea is that multiplying identities must not multiply power for free. To achieve this, voting weight is tied to a costly, verifiable resource. There are several mechanisms. Work (Proof of Work), where power is spent computation and energy. Stake (Proof of Stake), where power is locked capital, with slashing if you misbehave. Identity or authority (Proof of Authority), where power is membership in an authorized set. And proof of personhood, which binds a single human identity through biometrics or credentials.

Without Sybil resistance, the node count of a Byzantine fault tolerant system means nothing, because an attacker could simulate thousands of nodes and cross the threshold. It is the piece that makes distributed voting honest. Its usefulness goes beyond consensus: it is critical in on-chain governance, in airdrops, where it stops a single person from claiming as thousands of wallets, in DAO voting and in reputation systems.

In practice, Bitcoin draws its Sybil resistance from Proof of Work and Ethereum from stake (32 ETH per validator plus slashing). Projects such as World ID apply biometric proof of personhood, and Gitcoin Passport aggregates credentials into a uniqueness score to defend quadratic funding against fake identities. Digital identity and KYC frameworks fit naturally with identity-based resistance schemes.