Adrià Torralba-Agell

As blockchain technology continues to transform the realm of digital transactions, scalability has emerged as a critical issue. This challenge has spurred the creation of innovative solutions, particularly Layer 2 scalability techniques like rollups. Among these, ZK-Rollups are notable for employing ZeroKnowledge Proofs to facilitate prompt on-chain transaction verification, thereby improving scalability and efficiency without sacrificing security. Nevertheless, the intrinsic complexity of ZK-Rollups has hindered an exhaustive evaluation of their efficiency, economic impact, and performance. This paper offers a theoretical and empirical examination aimed at comprehending and evaluating ZK-Rollups, with particular attention to ZK-EVMs. We conduct a qualitative analysis to break down the costs linked to ZK-Rollups and scrutinize the design choices of well-known implementations. Confronting the inherent difficulties in benchmarking such intricate systems, we introduce a systematic methodology for their assessment, applying our method to two prominent ZK-Rollups: Polygon zkEVM and zkSync Era. Our research provides initial findings that illuminate trade-offs and areas for enhancement in ZK-Rollup implementations, delivering valuable insights for future research, development, and deployment of these systems.

Blockchains face significant scalability limitations that currently prevent their mass adoption, despite their contribution to the transformation across various sectors. Layer 2 (L2) solutions emerge as a promising avenue to alleviate these limitations, offering scalability enhancements while trying to retain the core security guarantees of underlying blockchains. However, despite their increasing prominence, the security assumptions underpinning Layer 2 solutions have not been sufficiently scrutinized. Addressing this gap, this paper contributes a rigorous examination of the security assumptions inherent in the most used blockchain Layer 2 scalability solutions (Payment Channel Networks, Optimistic Rollups, Zero-Knowledge Rollups, Validium, and Volition), by compiling and specifying all security assumptions that permissionless blockchains rely on, as well as, the additional security assumptions that Layer 2 solutions currently need on top of the inherited ones. Our analysis reveals that Layer 2 solutions need additional security assumptions beyond those already established by their underlying blockchains (Layer 1, or L1). By delineating these assumptions and their implications, our research facilitates a deeper understanding of the security challenges in blockchain scalability solutions.

Layer 2 rollups improve Ethereum’s scalability by executing transactions off-chain while relying on on-chain verification for finality. Despite their growing importance with increasingly high stakes, rollups have received limited systematic security analysis. In this paper, we present a taxonomy of rollup architectures and examine their associated security threats. We identify three main architectural patterns, primarily determined by the design of the sequencer, a critical component that bridges off-chain transaction execution with on-chain finality. Our analysis also reveals inherent trade-offs between throughput, decentralization, and resilience, demonstrating that no single architecture simultaneously optimizes all these properties.

Permisionless blockchains provide transparency, but converting raw on-chain traces into research-ready assets still demands specialized infrastructure, highly specialized low-level technical expertise, and non-trivial cost. These frictions are especially evident in Layer 2 environments (where Polygon zkEVM is an example), due to its added complexity on top of an already complex system. To lower this barrier, we assembled and released the corpus of Polygon zkEVM activity from its genesis up until 2024, extracted from a synced node and indexed into analysis-friendly tables. In this work, we describe the collection and transformation pipeline carried out over the Polygon zkEVM data, and showcase a representative analysis on user behavior patterns. We conclude with open questions and paths for future work. Moreover, we publish our code, notebooks and dataset to promote reproducibility, independent access to the data, and community contributions.

The rise of Layer 2 (L2) solutions, including Payment Channel Networks, sidechains, and rollups, has aimed to tackle the scalability challenges of Layer 1 (L1) blockchains like Bitcoin and Ethereum. Among these, Zero-Knowledge Rollups (ZK-Rollups) have emerged as a compelling solution by utilizing zkSNARKs to bundle multiple transactions, thereby enhancing throughput and reducing costs. However, despite their technical sophistication, ZK-Rollups do not inherently provide transaction privacy, a common misconception given the “Zero-Knowledge" nomenclature. This paper explores the privacy limitations of ZK-Rollups, emphasizing the need for privacy-preserving features that align with the expectations set by their name. We also review the strategies being developed by various projects to address these limitations. Furthermore, we propose the community begin adapting other names for the technology, such as “Verifiable Rollup" (verRollup), “Incrementally Verifiable Computation Rollup" (ivcRollup), or “Succinct Rollup" (sucRollup) that better represent the current capabilities of rollups. This work contributes to the ongoing discussion on achieving a balance between efficiency, scalability, and privacy in blockchain technologies.