Rollup Basics

What Is a Rollup?

A rollup is a blockchain that derives some of its security from another blockchain called a data availability layer. Just like traditional blockchains, rollups can support myriad use cases - including tokens, NFTs, and smart contracts. But, compared with other kinds of blockchains, rollups are much cheaper to operate.

Why are Rollups Cheap to Operate?

In a traditional blockchain, the work of applying each transaction to the ledger is duplicated across a globally distributed network of computers called full nodes. The larger this network is, the more secure the blockchain. But, since every full node has to process every transaction, the throughput of the chain needs to stay relatively low. Otherwise, the cost of running a full node will increase, which will discourage users from running nodes and weaken the chain’s security.

To avoid this issue, rollups don’t require most of their nodes to process transactions at all. Instead, they outsource transaction processing to a few beefy computers called sequencers. These sequencers accept transactions from users and apply them to the rollup’s ledger in real time.

Every few minutes, the sequencers checkpoint the rollup ledger onto the data availability layer (the underlying blockchain) by submitting a cryptographic commitment to the rollup’s latest state. When this happens, the rollup nodes verify that the new commitment is valid - either by checking a cryptographic proof or by waiting to see if anyone disputes the update. (Rollups that rely on cryptographic proofs of validity are called zk-rollups, while rollups that rely on honest parties to dispute invalid updates are called optimistic rollups.)

Since verifying a commitment is a lot less work than validating the transactions directly, rollups can process many more transactions than traditional blockchains without sacrificing security.

What is the Internet of Rollups?

The internet of rollups is what we call a fleet of zk-rollups running on an optimized data availability layer like Celestia or Ethereum (after EIP-4844). Sovereign Labs is building software to create native connections between rollups - so that sending transactions between rollups feels less like “bridging” between separate blockchains and more like making a regular transaction. Thanks to the power of cryptography, cross-rollup transactions can be fast, cheap, and secure, with no need for trusted third parties or rent-seeking middlemen.

What is the Sovereign SDK?

The Sovereign SDK is a free and open-source toolkit for building zk-rollups that is currently under development.

At a high level, the Sovereign SDK aims to do three things. First, it will provide a standard interface that allows rollups to communicate with data availability layers. This standard interface will make it easy for rollups to deploy on new data availability layers - and for new chains to support existing rollups. Second, it will integrate with cryptographic compilers. Developers will be able to write their code in standard programming languages, and the SDK will automatically convert their business logic into a form that’s cryptographically verifiable. Finally, it will provide default implementations of common blockchain primitives like tokens, NFTs, and bridges.

What Use Cases will the Internet of Rollups Enable?

The internet of rollups will be able to do everything blockchains can do today - payments, DeFi, NFTs, and governance - but at much greater scale and lower cost than the blockchains of today. We also expect it to enable emerging use cases, like gaming and automatic bug bounties. And, of course, it will allow for new inventions that we can’t predict - applications which are only viable at the massive scale and low cost that zk-rollups provide.