## 4 Blockchain Technologies: Layer 1 and Layer 2
### Zero-Knowledge Rollups  
ZK rollups aggregate multiple transactions off-chain and provide cryptographic proof of the validity of transactions without disclosing any specific transaction data. Subsequently, this verification, in conjunction with the transaction data, is made publicly available on the Layer 1 chain. ZK rollups offer a significant benefit in that Layer 1 just needs to validate a single ZKP proof rather than each specific transaction. This procedure significantly reduces the computational workload required by Layer 1, enabling quicker transaction processing and higher throughput [48].  
ZK proofs, such as zkSTARKs and zkSNARKs, are becoming increasingly popular in the blockchain world. These technologies facilitate the ability of one party to demonstrate to another party their knowledge of something without really disclosing the information itself. Both solutions are designed to enhance privacy and scalability by minimizing the required information exchange between users. zkSNARKs stands for Zero-Knowledge succinct noninteractive argument of knowledge. They lack interactivity, allowing the code to be deployed and operated alone. zkSNARKs rely on elliptic curves to ensure their security and necessitate a trustworthy setup. The dependence on a trusted set-up has raised concerns among critics, although developers only require its use in the beginning stages. Since there are no confidential data used in the blockchain implementations, the community dropped zk and instead uses SNARKs and STARKs.  
However, STARKs have bigger proof sizes, resulting in longer verification processes and requiring a greater amount of gas. Although the documentation for STARKs is not as detailed as that for SNARKs, the technical community has created a more comprehensive range of resources for individuals interested in implementing this state-of-the-art technology [53; 54].  
StarkNet utilizes STARKs to offer scalable and transparent anonymity on the blockchain. The decision to use STARKs instead of SNARKs is based on the former's superior scalability and the absence of a trusted setup. This makes it an effective solution for building decentralized applications that demand robust security and privacy. Miden, Polygon ZKEVM, zkSync, and Scroll are projects that frequently employ SNARKs to improve the scalability and privacy of Ethereum such as zkSync [23], Polygon zkEVM [24], Scroll [25]. Taiko would select its ZK proof technology based on its particular objectives for scalability, privacy, and the necessity for a trusted setup. They usually choose between zkSTARKs and zkSNARKs based on their needs for privacy, scalability, and not needing a trusted setup [55; 56].  
Several projects are leading the way in zkRollups to enhance scalability and efficiency in blockchain networks, particularly in Ethereum. Scroll enhances the overall efficiency and interoperability of the dApps with existing EVMs. By utilizing ZK proofs, this system verifies transactions without revealing any details. This enhances efficiency and decreases expenses, all while upholding Ethereum's level of security. zkSync ensures cost-effective transactions and efficient processing, enabling Ethereum developers to smoothly transfer their existing dApps. Polygon is a zkRollup that is completely identical to the EVM, guaranteeing compatibility with all current Ethereum contracts and tools. StarkNet is a decentralized system based on zkRollup technology that focuses on facilitating scalable transactions while keeping costs at a minimum. Taiko aims to be user-friendly for developers while maintaining optimal performance and security [48].