Rollup

A rollup is a mechanism that allows transactions to be executed outside layer 1 and then the data is posted to layer 1 where consensus is reached. As transaction data is included in layer 1 blocks, this allows rollups to be secured by native Ethereum security.

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).

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.