Rollup

A rollup is a mechanism that allows transactions to be executed on a separate blockchain while inheriting the availability and integrity guaranteed 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). As transaction data is included in layer 1 blocks, this allows rollups to be secured by native Ethereum security.

There are two types of rollups with different security models:

1. Optimistic rollups: assumes transactions are valid by default and only runs computation, via a fraud proof, in the event of a challenge.
2. Zero Knowledge rollups rely on mathematical proofs, which are difficult (computationally intensive) to create, but relatively easy to verify.