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Finality design

This page describes application-level and settlement finality in a LinethLineth (Formerly the Linea Stack) The open-source ZK-rollup stack, codebase, and technical protocol that's the foundation of Linea Mainnet. Operators can deploy this stack to launch their own Ethereum-compatible L2 or L3 networks. deployment. Timing and irreversibility depend on validator topology, consensus assumptions, proof generation and submission, and the selected finalization layer.

Application-level and settlement finality​

Finality is the point at which a transaction becomes immutable under the deployment's security assumptions. Instant finality means a block becomes final before the next block is produced, giving immediate application-level finality. For enterprise deployments, distinguish between:

  • Application-level finality: when a transaction is accepted as final by the configured network. With instant finality, this happens at block production.
  • Settlement finality: when the corresponding state commitment is verified and finalized on the selected finalization layer

L2Layer 2 (L2) A separate blockchain that increases transaction speed and throughput, while deriving its security from Ethereum. L2s rely on Ethereum for data availability by posting their transaction data onto Ethereum. blockchains bundle transactions and submit them to the L1Layer 1 (L1) The underlying foundation and base blockchain that various L2 networks build on top of. For example, Ethereum is an L1 that is comprised of node operators to secure and validate the network, block producers, the history of transaction data, and the consensus mechanism of the blockchain itself. blockchain. Soft finality occurs when a block is confirmed and committed on the L2. Hard finality occurs when the L2 state that includes the transactions is confirmed and committed on the L1. On a network built on Lineth, block production provides fast L2 confirmation before settlement on the finalization layer.

Standalone Lineth​

In a standalone deployment, application-level finality depends on the configured validator model. A single-validator deployment has explicit operator trust assumptions. A multi-validator deployment can use QBFT Quorum Byzantine Fault Tolerance (QBFT) The Byzantine-fault-tolerant consensus algorithm that Maru implements to let a validator set produce and finalize blocks, tolerating faulty validators in a 3f+1 validator set. consensus to finalize blocks among the authorized validators. For topology and latency trade-offs, see Multi-validator consensus.

Layer 2 Lineth​

As an L2 blockchain, zk-SNARKzk-SNARK (Zero-Knowledge Succinct Non-interactive Argument of Knowledge) A type of ZK proof where the prover and verifier don't have to interact. With zk-SNARKs, you can verify 1 transaction or 1 billion transactions in the same amount of time. proofs let the finalization layer verify committed L2 state without an optimistic-rollupOptimistic rollup A rollup of transactions that use fraud proofs to offer increased L2 transaction throughput while using the security provided by Mainnet (L1). Unlike Plasma, a similar L2 solution, optimistic rollups can handle more complex transaction types – anything possible in the EVM. However, in order to release assets back on the L1, users must wait for a seven-day challenge period. Liquidity providers can help alleviate distributing L1 ETH immediately, but this relies on trust in the security of the provider, and doesn't provide a mechanism for transferring NFTs. challenge window. Settlement timing still depends on proof generation, proof submission, and finality on the selected finalization layer.

Finality time as an operator decision​

Soft finality is reached at the block boundary. The public network uses 1-second block times; operators can choose parameters that fit their own latency, throughput, and validator-topology requirements.

When running a single validator, block production depends on that validator's availability and operating environment. When running a validator set, network latency and validator performance affect block validation time, while the consensus protocol defines when a block is finalized by the validator set.

Next steps​

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