A rollup is a mechanism that allows transactions to be executed on a separate blockchain while inheriting the availability and integrity guarantees of Ethereum itself (also called L1 Ethereum). Rollups achieve this goal by writing all transactions into L1 Ethereum as calldata, and then writing a hash of the transaction result (the state of their blockchain after the transaction).
Rollups use one of two mechanisms to convince the rest of the network that the result is correct:
- Optimistic rollups rely on verifiers that challenge incorrect results.
- Zero Knowledge rollups rely on mathematical proofs, which are difficult (computationally intensive) to create, but relatively easy to verify.