Sybil Attack

A Sybil attack is an attempt to control a peer-to-peer network by creating many fake identities that appear to be independent participants. The name comes from Sybil, a 1973 book about a woman with multiple personalities, and was coined in a 2002 paper by Microsoft researcher John Douceur, who showed that open networks cannot cheaply distinguish one entity pretending to be thousands.

How it works

Any system that counts votes, reviews, or peers by identity is vulnerable, because digital identities cost almost nothing to mint. In bitcoin's context, an attacker could spin up thousands of nodes, but node count deliberately carries no weight in consensus. Influence over the chain is priced in proof of work: each hash attempt costs real energy, so a thousand fake miners with no hardware have exactly zero say. Satoshi Nakamoto's white paper framed this as one-CPU-one-vote, replacing unverifiable identities with unforgeable expenditure. Sybil pressure survives at the network edge, where an attacker surrounding a node with hostile peers can attempt an eclipse attack, feeding it a false view of the chain; running multiple connections and diverse peer sources mitigates this.

In the gold vs bitcoin debate

Gold never needed Sybil resistance, since atoms cannot be faked into existence by registering new accounts. Bitcoin had to invent an equivalent for the digital realm, and its energy expenditure is exactly that invention: scarcity of identity replaced by scarcity of work. Critics who call mining wasteful and defenders who call it essential are describing the same design decision from opposite sides.