Leader election

The selection method determines three critical properties: fairness (proportional to stake), unpredictability (resistance to DoS or censorship against the leader) and resistance to randomness manipulation. It is the point where liveness and security meet. There are several verified approaches. The weighted round-robin of Tendermint and CometBFT rotates deterministically through the validator set with weight proportional to stake: simple, but the next leader is known.

RANDAO, in Ethereum proof of stake, is a collaborative randomness beacon: proposers contribute unpredictable, verifiable values that are aggregated into the beacon state RANDAO mix and select proposers and committees. Its known weakness is the last-revealer attack, where the final contributor can withhold its input if the result does not favor it. Algorand cryptographic sortition with a VRF avoids that vector: each ALGO holder runs a Verifiable Random Function locally with its secret key and is selected if the output falls below a stake-weighted threshold.

The private lottery of Ouroboros in Cardano lets each validator check its slot eligibility privately, with no public leader announcement, which prevents targeted attacks. Ethereum is researching the same via Whisk and single secret leader election (SSLE). For a company designing a network, choosing the leader election method well defines the balance between performance and censorship resistance. The named examples: RANDAO on Ethereum, VRF sortition on Algorand (Silvio Micali's design), private lottery on Cardano and weighted round-robin on Cosmos.