Proposer

3 min read

Pronunciation

[pruh-poh-zer]

Analogy

Think of a proposer as the temporarily appointed chairperson in a large committee meeting. While all committee members (validators) have equal authority to participate in discussions and voting, for each agenda item (block), one specific member is designated as the chairperson who organizes the topic, collects all relevant information, and presents a structured proposal for the rest of the committee to consider. This role rotates systematically among qualified members, giving everyone proportional opportunities to lead discussions based on their seniority or investment in the organization (stake). Just as the chairperson doesn't make final decisions alone but rather organizes information for collective approval, a proposer doesn't unilaterally add blocks to the chain but submits structured proposals for peer validation.

Definition

In systems, especially networks, a proposer is a temporarily designated to create and submit a new to the network. The proposer collects pending transactions, assembles them into a valid structure, and broadcasts this proposed for validation by other network participants, with different protocols using various methods to select which serves as proposer for each .

Key Points Intro

The proposer role implements four key functions in modern systems.

Key Points

Transaction Collection: Aggregates pending transactions from the mempool into candidate blocks according to inclusion rules and capacity constraints.

Block Creation: Assembles transactions with required metadata into a valid block structure that follows protocol-specific formatting rules.

Reward Attribution: Typically receives higher rewards than regular validators for the additional service of block composition and proposal.

Rotating Selection: Is chosen from the validator set through various methods including random selection, round-robin scheduling, or stake-weighted probability.

Example

In 's system, for each 12-second slot, one from the of over 500,000 validators is randomly selected to be the proposer. When Bob is selected as proposer for slot 4751603, his automatically gathers pending transactions from the network's , prioritizing those with higher prices to maximize fee revenue. Bob's constructs a valid containing these transactions, the previous 's , a , and other required fields, signing it with his key. He then broadcasts this proposed to the network. Other validators assigned to committees for this slot verify Bob's , checking that it follows all rules, and submit attestations confirming its validity. For successfully proposing this , Bob receives both the standard reward that all participating validators get plus an additional proposer reward, which includes a portion of the (though most are burned). The selection probability was proportional to Bob's , with his 32 ETH giving him approximately a 1 in 500,000 chance of being selected for each slot, meaning he statistically proposes a roughly once every 69 days.

Technical Deep Dive

Proposer selection mechanisms vary substantially across protocols, implementing different approaches to balance security, fairness, and predictability. Randomized selection protocols like 's use cryptographic sortition based on verifiable random functions (VRFs) or RANDAO-style commit-reveal schemes to generate unpredictable but verifiable proposer sequences, typically with selection probability proportional to . rotation systems like EOS's use fixed schedules where production rights cycle through a elected set of proposers in a predetermined sequence. implements a two-phase committee selection where a larger set of potential proposers is first identified, with the lowest value among their VRF outputs determining the actual proposer. The technical implementation of the proposer role typically involves several components: management systems for collection and prioritization, template generation algorithms that optimize inclusion for various objectives (fee revenue, efficiency, etc.), cryptographic operations for signing, and network communication protocols for efficient propagation. Modern systems often implement proposer boosting in choice rules, giving additional weight to chains containing blocks from the current slot's assigned proposer to enhance convergence. Advanced proposer designs include features like proposer/builder separation (PBS) where specialized entities optimize construction while proposers simply select and sign the most profitable , reducing centralization pressures.

Security Warning

When a has predictable proposer selection or long gaps between assignment and proposal time, proposers may face increased risk of targeted denial-of-service attacks. If operating as a proposer in such systems, consider implementing additional network security measures during your assigned proposal slots.

Caveat

While the proposer model enhances efficiency by assigning creation to specific validators, it can introduce points of temporary centralization in the process. If a selected proposer is unavailable or censoring transactions, the network typically must wait for the next proposer selection rather than immediately failing over to alternatives, potentially creating temporary throughput reductions. Additionally, as economics have evolved, proposers gain significant power in ordering, enabling maximal extractable value (MEV) extraction that may create centralization pressures favoring sophisticated proposers with advanced profit optimization capabilities. Various protocols are exploring mechanisms like proposer/builder separation to these concerns, but the tension between efficient production and decentralized ordering remains an active area of development.

Related Terms

Validator

Block Reward

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