Understand the importance of pursuing a user-centric model in rollups and the role of Radius in that vision.

Introduction

The basics of growth for any successful product or service are long-term users. In an ideal world, you wouldn’t have to worry about users churning away.

The reality. Today’s users might not be your users tomorrow.

This challenge extends to rollups and decentralized applications within blockchain ecosystems, particularly in environments where users have the ease and flexibility to hop on and off between rollups and applications. Achieving usage growth isn’t enough when users don’t stick around for long.

Why rollups need to put users first

Despite the rapid shift towards a modular world and the promising scalability potential of rollups, creating a sustainable rollup ecosystem remains inherently challenging. This challenge arises from both existing rollup designs and the pain points faced by users:

• Censorship and harmful MEV risks: Rollups rely on centralized sequencers to receive and order user transactions, exposing users to risks such as censorship and harmful MEV (frontrunning, sandwiching). These risks undermine trust in rollups, as transaction orders can be manipulated and reordered for the benefit of the sequencer. Censorship and harmful MEV are strictly problematic — from both a regulatory perspective and by threatening users with unfair transaction execution and loss of funds.

• No finality guarantees on Ethereum: Users expect their transactions to be executed in a specified order and achieve finality on Ethereum (as preconfirmed by the rollup). While rollups guarantee the correct execution of transactions, there is no certain guarantee for inclusion on Ethereum. The lack of incentive alignments between Ethereum and rollups exacerbates this issue; for example in cases where rollup transactions aren’t as profitable for the L1 proposer. Without strong finality guarantees, users experience untold frustration, which again leads to a loss of trust in the rollup.

• Poor interoperability user experience: User experience remains one of the biggest bottlenecks in blockchains. Navigating across different applications, especially across multiple rollups, incurs high friction. Users must rely on bridges or go through Ethereum itself, which is inconvenient and cumbersome. With thousands of rollups on the horizon and anticipated demand for frequent cross-rollup transactions, making the user experience as frictionless as possible and abstracting away complexity becomes essential.

Resolving user pain points becomes crucial in practice as the rollup ecosystem grows: ensuring transaction security, fast finality, and a seamless experience for interoperability. These pillars are foundational for rollups to thrive in a competitive landscape and provide long-term value to users.

Radius: The key ingredient for building a user-centric rollup

In our pursuit to build a user-centric rollup ecosystem, we’ve created Radius, a novel and secure sequencing solution powered by cryptography, providing fast finality and seamless interoperability.

Radius is a fundamental component in rollups—orchestrating a secure and seamless transaction journey from within—and contributing to their scalable growth.

Here are the guiding principles underpinning our vision for user-centric rollups:

Secure transactions from censorship and harmful MEV

Keeping transactions secure and safe is the first step towards building a user-centric rollup. Radius ensures the security of transactions by encrypting transactions using a trustless sequencing engine to prevent sequencer attempts to censor, frontrun, or sandwich them. Transactions remain encrypted until sequencers preconfirm the order (with delay encryption) and encrypted transactions are verified with zero-knowledge proofs (ZKPs), eliminating the amount of trust placed in sequencers.

In Radius, preconfirmations ensure that transactions are free from censorship and harmful MEV and executed in the correct order.

Learn more about our approach using delay encryption and zero-knowledge proofs (ZKPs) for encrypted mempools.

Fast Finality

The objective of fast finality is to provide users with high certainty that their preconfirmed transactions will be finalized on Ethereum without relying on the trust of the rollup. This certainty enables users to move on with creating the next transactions without having to wait for finalization on Ethereum.

A crucial aspect of achieving fast finality is the inclusion guarantee on Ethereum. However, this guarantee cannot be solely ensured by the efforts of the rollup. To achieve this, Radius uses mechanisms like based sequencing to align incentives between Ethereum and rollups, fostering a mutually cooperative ecosystem. This ensures preconfirmations for fast finality, regardless of the entity providing them.

Incentive alignment mechanisms, combined with our trustless sequencing engine for censorship and harmful MEV resistance, enable rollups to inherit fast finality guarantees and enhance economic security.

Our previous developments include preconfirmation guarantees for censorship and harmful MEV resistance (as demonstrated in Curie Testnet) and preconfirmation guarantees in cases of sequencer failures (demonstrated in Portico Testnet), where a failed leader delegates its sequencing rights to a follower.

Seamless Interoperability

The fragmentation of rollups and complexity in their communication arise from the absence of a shared entity. Shared sequencers act as a mechanism for unifying rollups providing seamless interoperability experiences. This means users are given the simplest, most seamless journey as they engage with various rollups.

Moreover, shared sequencers facilitate state synchronization among rollups, regardless of their execution environments (or different block times). This unlocks opportunities for atomic transactions, eliminating the need for rollup sequencers to give preconfirmations individually or communicate directly for cross-rollup transactions.

Learn about our approach to achieving atomic execution with shared sequencers.

Rollup Benefits

As much as rollups need to prioritize their end-users, we recognize the importance of catering to our users—the rollups.

Rollups can benefit from 1) autonomy in sequencing 2) a selective composability solution tailored to their composability needs and 3) earning user-protected revenue.

Autonomy in sequencing: Rollups have flexible sequencing options that that align with their values and goals.

If rollups desire full control over their sequencing rights, they can simply run the trustless sequencing engine that is built within the rollup to ensure the security of transactions granting censorship and harmful MEV resistance, inherit fast finality, and seamless interoperability features.

Selective composability: With selective composability, rollups can choose which other rollups to communicate with based on their preferences and requirements. This approach allows rollups with different execution environments to achieve customized scalability.

For example, a rollup in the ZK stack ecosystem may choose to communicate exclusively with select rollups within the same ecosystem (and similarly for Madara, Polygon CDK, OP Stack, Arbitrum Orbit rollups).

Rollups also have the flexibility to opt out of selective composability as needed.

User-Protected Revenue

Rollups continue to generate revenue while protecting users from censorship and MEV activities.

Blockspace is divided into two: top-of-block (ToB) and bottom-of-block (BoB). BoB is specifically dedicated to encrypting user transactions, protecting them censorship, fronrunning, and sandwiching through the built-in trustless sequencing engine. Meanwhile, rollups can build ToB for revenue (or allocate ToB building rights to builders), where they can include backrunning bundles based on the rollup’s previous block state.

Learn about our approach to ensuring revenue generation for rollups.

Rollups with a user-first mindset

While blockchains strive to be a secure, scalable, and decentralized network, the current mismatch in system design and value extraction presents challenges for Ethereum rollups to adopt a user-centric approach.

To address these challenges, rollups require finding the right guardrails prioritizing transaction security, fast finality, and seamless interoperability values that center around the users.

As part of the expanding modular ecosystem working to optimize rollup efficiency, Radius helps rollups navigate through these challenges for users to transact securely and confidently—creating a strong, resilient, and sustainable rollup ecosystem.