LAYER-2 WIKI

An isometric encyclopedia of Layer-2 blockchain technology

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Index

Explore the building blocks of Layer-2 technology

Rollups

Bundle hundreds of transactions off-chain before posting compressed data to Layer 1.

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Rollups

Rollups are the dominant Layer-2 scaling approach. They execute transactions off the main chain but post transaction data on-chain, inheriting the security of Layer 1. Two main varieties exist: optimistic rollups (assume valid, fraud-proof challenged) and zk-rollups (prove validity via zero-knowledge proofs). Examples include Arbitrum, Optimism, zkSync, and StarkNet.

State Channels

Off-chain pathways allowing two parties to transact rapidly without touching the main chain.

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State Channels

State channels allow participants to conduct numerous transactions off-chain while only submitting two on-chain transactions: one to open and one to close the channel. The Lightning Network for Bitcoin is the most prominent example. Participants lock funds in a multisig contract, exchange signed state updates off-chain, and settle the final state on Layer 1. Ideal for frequent, bidirectional payments between known parties.

Plasma

A framework for creating child chains anchored to the main Ethereum chain.

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Plasma

Plasma creates a tree of child chains that periodically commit state roots to the main chain. Each child chain can have its own consensus mechanism and block validation rules. Originally proposed by Vitalik Buterin and Joseph Poon in 2017. While largely superseded by rollups for general computation, Plasma remains relevant for specific use cases like NFT transfers and simple payment scenarios where data availability requirements are lower.

Validium

Like zk-rollups but with off-chain data availability for higher throughput.

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Validium

Validium uses zero-knowledge proofs like zk-rollups but stores data off-chain with a Data Availability Committee (DAC). This trades some security for dramatically higher throughput — up to 10,000+ TPS. StarkEx powers several validium deployments including dYdX and Immutable X. The key tradeoff: if the DAC goes offline, users cannot reconstruct state and prove ownership of their assets.

Sidechains

Independent blockchains with their own consensus, connected to the main chain via a bridge.

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Sidechains

Sidechains operate as separate blockchains with their own validators and consensus mechanisms. They connect to the parent chain through a two-way bridge (or peg). Polygon PoS (formerly Matic) is the most widely used example. Unlike rollups, sidechains do not inherit security from Layer 1 — they are responsible for their own security guarantees, making the trust model fundamentally different.

Zero-Knowledge Proofs

Cryptographic method to prove a statement is true without revealing the underlying data.

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Zero-Knowledge Proofs

ZK proofs allow one party (prover) to convince another (verifier) that a computation was performed correctly without revealing the inputs. Two main proof systems dominate: zk-SNARKs (succinct, require trusted setup) and zk-STARKs (transparent setup, quantum-resistant, larger proofs). These underpin zk-rollups and enable private, verifiable computation at scale.

Optimistic Rollups

Assume transactions are valid by default and use fraud proofs if challenged.

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Optimistic Rollups

Optimistic rollups "optimistically" assume all transactions are valid. A challenge period (typically 7 days) allows anyone to submit a fraud proof if they detect an invalid state transition. Arbitrum uses interactive fraud proofs while Optimism uses non-interactive single-round proofs. The main tradeoff is withdrawal latency — users must wait through the challenge period to move assets back to Layer 1.

Data Availability

Ensuring that all data needed to verify a chain's state is accessible to all participants.

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Data Availability

Data availability (DA) is the guarantee that block data has been published and is retrievable by any network participant. Without DA, users cannot verify state transitions or prove ownership. Ethereum's EIP-4844 (proto-danksharding) introduces blob-carrying transactions to reduce DA costs for rollups. Dedicated DA layers like Celestia and EigenDA offer alternative solutions with Data Availability Sampling (DAS).

Bridges

Protocols that enable asset and message transfer between Layer 1 and Layer 2 networks.

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Bridges

Bridges connect separate blockchain networks, enabling cross-chain asset transfers and messaging. Trust models vary: native bridges (secured by L1 validators), externally verified (rely on a separate validator set), and locally verified (trust only the counterparty). Bridge exploits have accounted for billions in losses, making bridge security one of the most critical research areas in the space.

Deep Dive

Extended explorations of key Layer-2 concepts

The Rollup-Centric Roadmap

Ethereum's long-term scaling strategy centers on rollups as the primary execution layer. Rather than increasing Layer 1 throughput directly, the roadmap envisions Ethereum as a data availability and settlement layer — a secure foundation upon which rollups perform computation.

This approach preserves decentralization at the base layer while enabling orders-of-magnitude throughput improvements at Layer 2. With EIP-4844 and the forthcoming full danksharding upgrade, rollup transaction costs are expected to drop by 10-100x, making micro-transactions economically viable.

The competition between optimistic and ZK approaches drives rapid innovation. Optimistic rollups currently dominate TVL due to EVM equivalence, while ZK rollups promise faster finality and stronger security guarantees as proof generation becomes more efficient.

The Zero-Knowledge Revolution

Zero-knowledge proofs represent a fundamental breakthrough in cryptography, enabling one party to convince another that a statement is true without revealing any information beyond the validity of the statement itself.

In the context of Layer-2 scaling, ZK proofs allow a rollup operator to generate a compact validity proof that certifies the correctness of thousands of state transitions. The Layer 1 contract verifies this proof in constant time, regardless of how many transactions were batched.

The two dominant proof systems — SNARKs and STARKs — offer different tradeoffs. SNARKs produce smaller proofs but require a trusted setup ceremony. STARKs are transparent (no trusted setup) and quantum-resistant but generate larger proofs. Recursive proof composition allows proofs of proofs, enabling virtually unlimited scalability.

Protocol Map

How Layer-2 protocols relate to each other