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How It Works

Leios is a high-throughput overlay protocol designed to enhance blockchain scalability, such as for Cardano’s Ouroboros, by managing a structured flow of transactions. Here’s a breakdown of how it operates:

  1. Creating Input Blocks (IBs):
    Stake pool operators (SPOs), acting as validators, bundle transactions into Input Blocks (IBs) every 0.2–2 seconds and broadcast them across the network for parallel processing.

  2. Proofs of Data Availability:
    Validators check that IBs’ transaction data is valid and accessible, a process later confirmed through Endorser Blocks (EBs) and voting, ensuring no data is missing or malformed.

  3. Generating Endorser Blocks (EBs):
    EBs aggregate multiple verified IBs, grouping them for validation and proposing their inclusion in the blockchain’s final ledger.

  4. Pipelined Processing:
    The protocol uses a seven-stage endorsing pipeline (detailed below) to process IBs, EBs, and votes in parallel, maximizing network bandwidth and throughput.

  5. Voting and Certification:
    Validators vote on EBs using stake-weighted BLS signatures to certify their correctness and data availability, ensuring only compliant IBs (e.g., valid scripts) proceed.

  6. Final Inclusion in the Blockchain:
    Certified EBs are referenced by a certificate included in a Ranking Block (RB)—a Praos-style block minted every ~20 seconds—finalizing IB transactions on the blockchain while maintaining a verifiable, efficient record.

Leios architecture​

The Leios protocol utilizes a pipelined architecture to achieve high throughput. A pipeline instance comprises seven stages:

  1. Propose:

    • Validators concurrently generate and propose IBs with transaction data, kicking off the pipeline instance and targeting frequent output (e.g., every 0.2–2 seconds).
    • IBs proposed during this stage are the focus of the current pipeline instance.

  2. Deliver1:

    • Time is allocated for proposed IBs to spread across the network using a freshest-first diffusion strategy, ensuring honest nodes receive them within a set delay (e.g., Δ_hdr) despite potential adversarial bursts.
    • Duration is crucial for ensuring all honest nodes receive IBs before the next stage.

  3. Link:

    • Validators create EBs that reference Propose-stage IBs, grouping and ordering them for validation and eventual blockchain inclusion.
    • EBs serve as containers for grouping and ordering IBs.

  4. Deliver2:

    • Time is allocated for any adversarial IBs referenced by EBs to disseminate, ensuring honest nodes have all data needed for fair voting and availability checks.
    • Ensures honest nodes have received all relevant IBs before casting votes.

  5. Vote1:

    • Validators cast stake-weighted votes (via BLS signatures) for EBs from the Link stage, certifying them as Vote1-certified if enough votes confirm their IBs’ validity and availability.

  6. Endorse:

    • New EBs reference Vote1-certified EBs, linking across pipeline instances to reinforce IB confirmation and ensure high throughput by cross-referencing honest data.
    • Strengthens overall confirmation of IBs.

  7. Vote2:

    • Validators cast final votes for Endorse-stage EBs, certifying them as Vote2-certified if they reference a majority of Vote1-certified EBs, preparing them for RB inclusion and ledger finality.
    • Must reference a majority of Vote1-certified EBs.

Network Resilience​

Leios counters adversarial tactics with:

  • Freshest-First Diffusion: Nodes prioritize downloading the newest IBs and EBs (via VRF-based timestamps), limiting delays from malicious message bursts.
  • Equivocation Proofs: If a validator double-signs (e.g., sends conflicting EBs), honest nodes detect and propagate proofs, ensuring only one valid block per slot is processed, minimizing bandwidth waste.

Integration with Ouroboros​

  • Leios enhances Ouroboros Praos by overlaying its Ranking Blocks (RBs) with high-throughput IB and EB processing. RBs, minted every ~20 seconds, anchor the ledger’s security, while Leios’ pipeline scales transaction capacity without altering Praos’ core settlement guarantees.

This pipelined architecture ensures continuous IB generation, parallel processing, and robust confirmation, enabling Leios to achieve near-optimal transaction throughput (e.g., (1-δ) of network capacity) while resisting adversarial tactics like message bursts and equivocations.