Consensus Round

The round begins with a designated node, the proposer or leader, creating a candidate block of transactions. In Proof-of-Stake (PoS) systems, proposers are often chosen via a weighted random selection based on stake. This phase is critical for liveness, as a faulty proposer can stall the round.

Other network participants, known as validators or committee members, receive the proposed block. They independently execute the transactions and cryptographically verify its correctness (e.g., signatures, state transitions). Validators then broadcast their votes (e.g., pre-votes, pre-commits) to signal acceptance or rejection.

The round concludes when a supermajority (e.g., 2/3) of validators agree on the same block. This agreement is recorded on-chain as a commit, making the block final and immutable. Finality can be probabilistic (Bitcoin) or deterministic (Tendermint, Ethereum's finality gadget).

A consensus round operates within a predefined time interval called a slot. In networks like Ethereum, each slot (12 seconds) is a chance for a valid proposal. A sequence of slots forms an epoch, which is used for validator reassignment and rewards distribution. Round duration directly impacts time-to-finality.

This is the algorithm that determines the canonical chain when multiple valid blocks are proposed. Key rules include:

• Longest Chain Rule: Used in Nakamoto consensus (Bitcoin).
• GHOST / LMD-GHOST: Used by Ethereum to account for uncles.
• Heaviest Observed SubTree: A variant that considers validator votes.

The method for selecting the round's proposer is central to security and fairness. Common mechanisms are:

• Proof-of-Work: Random, based on hash rate.
• Proof-of-Stake: Weighted random selection from the validator set.
• Round-Robin: Deterministic, sequential rotation among known validators (common in BFT protocols).

The core security trade-off in a consensus round. Liveness ensures the network continues to produce new blocks (progress). Safety guarantees all honest nodes agree on the same block (consistency). A round must balance these; a network halted by a liveness failure is unavailable, while a safety failure results in a fork.

The mechanism preventing a single entity from controlling multiple identities (Sybils) to influence the round. Proof-of-Work uses computational cost, Proof-of-Stake uses economic stake. Weak Sybil resistance allows 51% attacks, where an attacker can dominate the voting process in a round to double-spend or censor transactions.

The irreversible confirmation of a block within a round. Probabilistic finality (Bitcoin) means reversal probability decreases over time. Absolute finality (Tendermint, Ethereum post-merge) is achieved after a round's voting threshold is met, making reversion economically impossible without slashing. A round without clear finality is vulnerable to reorgs.

The security of a round depends on the honesty and decentralization of the validator set. Key risks:

• Cartel Formation: A small group colluding to control rounds.
• Single Point of Failure: Centralized cloud hosting for validators.
• Slashing Conditions: Penalties for malicious actions (e.g., double-signing) must be severe enough to deter attacks but not so severe they discourage participation.

Adversaries can target the round's communication layer. Eclipse Attacks isolate a validator to feed it a false view of the network. Network Partitioning (netsplit) can cause honest groups to finalize different chains, creating a fork. Latency Manipulation can disrupt the synchronous assumptions of some consensus algorithms, preventing timely agreement.

The round's security is underpinned by cryptoeconomic incentives. Validators must have skin in the game (staked assets) that can be slashed for misbehavior. The reward for honest participation must exceed the potential profit from attacking the round. The cost to attack (e.g., acquiring 51% of hashpower or stake) must be prohibitively high.

The initial phase of a consensus round where a designated participant, such as a validator or leader, creates and broadcasts a candidate block containing pending transactions. In Proof of Stake (PoS) systems, this right is often granted via a lottery or stake-weighted selection.

The validation phase where network participants vote on the validity of a proposed block. In Practical Byzantine Fault Tolerance (PBFT) and its derivatives, this involves explicit voting rounds. In Ethereum's Casper FFG, validators provide attestations as votes to justify and finalize blocks.

The irreversible confirmation of a block and its transactions at the end of a successful consensus round. Probabilistic finality (Bitcoin) means confidence increases with subsequent blocks. Absolute finality (Tendermint, finality gadgets) is a cryptographic guarantee that a block cannot be reverted without slashing a large portion of stake.

A safety procedure in leader-based BFT protocols (e.g., PBFT, HotStuff) that occurs when the designated leader for a round fails or acts maliciously. Validators vote to time out the current round and move to a new view with a different leader, ensuring liveness despite faulty nodes.

A larger time unit comprising multiple consensus rounds, used to manage validator sets and rewards. In Ethereum, an epoch is 32 slots (each slot is a chance for a block). Validator committees are shuffled per epoch, and finality is assessed over a two-epoch window.

A punitive mechanism in Proof of Stake systems that penalizes validators for malicious actions that violate consensus rules during a round, such as double signing blocks or casting contradictory votes. Slashing involves the loss of a portion of the validator's staked funds.