June 30 (Cointime) - Layer-2 blockchains built on top of Ethereum offer increased throughput and security, but assessing their level of security is complex and not always clear-cut. L2Beat provides a risk analysis framework for comparing active layer-2 options based on security-related criteria, with state validation being the most important factor. Four widely accepted varieties of Layer-2s exist, each with its own tradeoffs and suitability for specific use cases.

Arbitrum and Optimism are the first optimistic rollups to launch on the Ethereum mainnet, both using fraud proofs to secure their systems. Optimism initially used a simpler "single-round" proof design, but a subsequent audit showed that it was difficult to secure. To reach Stage 1, a rollup must have a functional proof system with at least five external actors who can submit fraud proofs, and users must be able to exit to Ethereum mainnet without permissioned operators.

Multi-signature wallet schemes are often used to manage smart contract upgradability, but permissionless withdrawals are insufficient to be secured by Ethereum if there is still a multisig that can unilaterally break security properties. Of the major rollups, only Arbitrum has reached Stage 1, but zero-knowledge tech is expected to become the standard for security and scalability.