Sidechain Storage

By moving data storage and computation off the main chain, sidechains significantly increase transaction throughput and reduce network congestion. This allows the main chain to focus on consensus and finality, while the sidechain handles bulk data operations. For example, a gaming dApp can process thousands of in-game asset transfers per second on a sidechain without burdening the main Ethereum network.

Sidechain storage dramatically lowers transaction fees (gas costs) by using a separate, often more efficient, consensus mechanism (e.g., Proof of Authority) and not competing for block space on the expensive mainnet. This makes microtransactions and frequent data writes economically viable, enabling use cases like play-to-earn gaming, high-frequency DeFi, and data oracles.

A critical feature is the secure, two-way peg mechanism that locks assets on the main chain and mints equivalent representations on the sidechain. This enables:

• Asset portability: Moving tokens (e.g., Wrapped BTC, ETH) between chains.
• Cross-chain communication: Triggering actions on the main chain from the sidechain.
• Data finality relay: Periodically committing sidechain state checkpoints to the main chain for enhanced security.

Sidechains can implement consensus models optimized for their specific use case, independent of the main chain. This allows for:

• Higher performance with PoA or DPoS for enterprise data streams.
• Enhanced privacy with zk-SNARKs or other cryptographic primitives.
• Tailored governance where sidechain validators manage upgrades and parameters, reducing main chain governance overhead.

Security is not inherited; it is provided by the sidechain's own validator set. Models vary:

• Federated: Trusted entities operate the bridge and consensus (e.g., early Polygon PoS).
• Proof-of-Stake: Validators stake native tokens to secure the chain (e.g., Polygon's upcoming zkEVM).
• Plasma & Rollups: Use cryptographic proofs to commit data to the main chain, with different data availability guarantees (e.g., storing data on-chain vs. off-chain).

Sidechain storage enables specific high-volume, low-cost applications:

• Gaming & NFTs: Immutable in-game assets and high-speed transactions (e.g., Polygon for NFT minting).
• Enterprise Data Logs: Supply chain tracking and audit trails.
• DeFi Scaling: High-frequency trading and micro-lending platforms.
• Data Oracles: Decentralized services like Chainlink can run cheaper, faster data feeds on a sidechain.

A core risk is ensuring data stored on the sidechain remains available to prove the state for withdrawals back to the main chain. If sidechain validators withhold data, users cannot generate the Merkle proofs required to exit. This is mitigated by data availability committees (DACs) or data availability sampling (DAS) in more advanced designs, but remains a critical failure mode.

The security model depends heavily on who controls the storage validators.

• Federated/Custodial: A trusted group manages the sidechain, introducing centralization and counterparty risk.
• Proof-of-Stake Non-Custodial: Validators are slashed for misbehavior, but a malicious majority can still censor or revert transactions.
• Zero-Knowledge (ZK) Rollups: The strongest model, where validity proofs posted to the main chain guarantee state correctness, making storage liveness the primary concern.

Sidechain finality is often weaker than the underlying L1. A deep reorganization (reorg) on the sidechain could invalidate transactions users assumed were settled, impacting bridges and cross-chain applications. The risk is highest for sidechains with probabilistic finality (e.g., PoW sidechains) versus those with fast finality that checkpoint to the main chain.

The smart contracts locking assets on the main chain and minting them on the sidechain are a prime attack surface. Historical exploits (e.g., Ronin Bridge, Wormhole) often target bridge logic or validator multisigs, not the sidechain storage itself. Secure bridge design requires time-delayed withdrawals, fraud proofs, or validity proofs to detect and challenge invalid state transitions.

If a malicious actor gains control of the supermajority of sidechain validators (e.g., via a 51% attack in PoS or a compromised multisig in a federation), they can:

• Censor transactions.
• Double-spend assets on the sidechain.
• Halt the chain, freezing all assets. This risk is amplified if the validator set is small or lacks economic stake slashed on the main chain.

Sidechain client software and smart contracts are frequently upgraded. A centralized or rushed governance process can introduce bugs or malicious code. The ability to upgrade bridge contracts or validator sets without sufficient delay or decentralization poses a systemic risk, as seen in incidents where admin keys were used to pause bridges or mint unlimited tokens.

The guarantee that all transaction data is published and accessible for network participants to verify state transitions. Sidechain storage must ensure data availability so validators can reconstruct the chain's state and detect fraud. Without it, a sidechain cannot be securely validated by its parent chain or other parties.

• Core Requirement: Essential for fraud proofs and validity proofs in optimistic and zk-rollups.
• Layers: Can be handled on-chain (expensive), by a committee, or via specialized data availability layers like Celestia or EigenDA.

The process by which a blockchain updates its global state (account balances, smart contract storage) based on a new block of transactions. A sidechain's storage system records the result of each state transition.

• Execution: The sidechain's virtual machine (e.g., EVM) executes transactions to compute the new state.
• Storage Commitment: The resulting state root (a cryptographic hash of the entire state) is stored and often published to the parent chain as a compact proof of the sidechain's current state.

A protocol that enables the transfer of assets and data between the sidechain and its parent chain (or other chains). The security and trust model of a bridge is intrinsically linked to the sidechain's storage and consensus.

• Asset Bridges: Lock tokens on the main chain, mint representations on the sidechain. The bridge contract must verify the sidechain's state, which depends on reliable storage.
• Messaging Bridges: Relay arbitrary data, requiring verification of transaction inclusion and finality proofs from the sidechain's stored history.

A mechanism where a sidechain periodically submits a summary of its state (e.g., a block hash or state root) to its parent chain. This anchors the sidechain's history into the more secure parent chain's ledger.

• Security Function: Allows users to prove the existence and state of sidechain transactions based on the parent chain's consensus.
• Storage Implication: Reduces the data that needs to be permanently stored on the parent chain, as only checkpoints are stored, while full history remains on the sidechain's nodes.

A scaling technique that horizontally partitions blockchain data across multiple committees or chains (shards). Sidechain storage can be viewed as a form of application-specific sharding, where each sidechain maintains its own independent state and transaction history.

• Parallelism: Different sidechains/shard s process and store transactions concurrently, increasing total throughput.
• Comparison: Unlike monolithic chains, sharded architectures (e.g., Ethereum's roadmap) and sidechain models both distribute storage and computation to overcome single-chain bottlenecks.

An older Layer 2 scaling framework that uses child chains (a type of sidechain) with periodic commitments to Ethereum. Plasma chains have their own block validation and storage, with users responsible for monitoring the chain and submitting fraud proofs.

• Storage Model: Relies heavily on users storing their own transaction history and relevant state data to challenge invalid exits.
• Evolution: Largely superseded by optimistic rollups, which improve usability by posting all transaction data to Layer 1, simplifying the storage and security model for users.