Rollups on Ethereum (enshrined settlement)
- Current rollups on Ethereum post their blocks directly to an EVM-based smart contract, also known as a bridge contract. This contract effectively implements an on-chain light client for the rollup, that receives block headers and processes fraud or validity proofs. In this model, there is an enshrined, hard coded, trust-minimized bridge to the Ethereum main chain.
- Using the bridge contract, users can deposit and withdraw assets between the rollup and the execution chain that the bridge contract lives on in a trust-minimized way, because the contract will not accept invalid blocks from sequencers, thanks to fraud or validity proofs.
- The Ethereum chain, acting as a consensus and data availability layer, only records and finalizes blocks that are valid according to the bridge contract. Thus the rollup full nodes and lights clients (outside of the smart contract) consider the Ethereum on-chain light client as the root source of truth as to what the canonical (correct) rollup chain is. In this model, we consider that Ethereum is enshrined as a coupled settlement layer for the rollup, where the rollup is a 'baby chain' to Ethereum rather than an independent chain in its own right.