  The rapid expansion of the use of blockchain-based systems often leads to a
choice between customizable private blockchains and more secure, scalable and
decentralized but expensive public blockchains. This choice represents the
trade-off between privacy and customization at a low cost and security,
scalability, and a large user base but at a high cost. In order to improve the
scalability of secure public blockchains while enabling privacy and cost
reduction, zk-rollups, a layer 2 solution, appear to be a promising avenue.
This paper explores the benefits of zk-rollups, including improved privacy, as
well as their potential to support transactions designed for specific
applications. We propose an innovative design that allows multiple zk-rollups
to co-exist on the same smart contracts, simplifying their creation and
customization. We then evaluate the first implementation of our system
highlighting a low overhead on existing transaction types and on proof
generation while strongly decreasing the cost of new transaction types and
drastically reducing zk-rollup creation costs.
