Sybil resistance

Sybil resistance is what stops one actor from cheaply pretending to be thousands of independent participants and thereby seizing control of a system that decides things by counting nodes. The name comes from a clinical case study of multiple-personality disorder: a Sybil attack is one entity wearing many masks. On an open, permissionless network where anyone can spin up unlimited identities for free, naive 'one node, one vote' consensus is trivially captured, so every blockchain needs a way to make identities, or influence, genuinely costly.

Blockchains do not try to verify real-world identity; they make participation expensive instead, so that controlling a majority of the voting weight costs a majority of some scarce resource. Proof of work ties influence to computation: to wield half the votes you must spend half the network's electricity and hardware. Proof of stake ties influence to capital: to wield half the votes you must bond half the staked value, which is at risk of slashing if you misbehave. In both cases, faking ten thousand nodes is pointless because ten thousand identities backed by no work or no stake carry no weight.

The crucial reframing is that consensus security is not about counting machines but about counting scarce resources. This is why a 51% attack is described in terms of hash power or stake, not node count, and why Sybil resistance is the precondition that makes the Byzantine fault tolerance threshold meaningful: the '3f+1 honest' bound only holds if an attacker cannot manufacture the votes to cross it. Other systems use different scarce anchors — proof of authority uses vetted identities, proof of space uses disk — but the principle is identical: bind voting power to something that cannot be conjured for free.