> For the complete documentation index, see [llms.txt](https://docs.zkopru.network/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.zkopru.network/arctic-roll/how-it-works.md).

# How it works

## Optimistic + RollUp + zk-transaction = zkopru

The "Optimistic" way in Ethereum means that we can skip the computation of a transaction by a challenge system if we provide enough data on-chain. Plasma Group brought up this concept to solve the data availability problem in the plasma solutions.

This concept gives us a significant advantage in computation. Especially for the implementation of the zk-transaction on Ethereum, it is necessary to use a SNARK-friendly hash function to construct a Merkle tree, which is usually very expensive on EVM. However, using the optimistic rollup, we can update the SNARK friendly Merkle tree at a low cost compare to computing it on-chain. As a result, this protocol consumes about 8,800 gas per private transaction.

Most of all, Zkopru can continuously upgrade itself because it supports mass migration, which allows moving assets to the other layer-2 network.