When "An Incomplete Guide to Rollups" was released on January 5, 2021, by Vitalik Buterin, the total TVL (total value locked) in Ethereum Layer 2 (L2) solutions was very low at around 75,000 ETH ($78M). At that time, it seemed as if the L2 market still had a way to go before reaching its potential. However, there are around 26 L2 projects now active, and the current total TVL for L2 is approximately 3.2 million ETH ($5 billion). This represents a rise of 42 times in terms of ETH and a growth of 64 times in terms of dollars. In particular, the two big optimistic roll-up projects Arbitrum and Optimism have risen to rank fifth and seventh, respectively, in the overall network TVL rankings. Now that the L2 market has reached such a widespread level of adoption, many consumers would experience a significant degree of inconvenience if L2 initiatives were to be discontinued. Numerous L2 projects came into being as a result of the expansion of the L2 market, and many of these projects went on to become well-known, including Arbitrum, Optimism, dYdX, zkSync, and Starknet. Even today, in spite of the vast number of networks that already exist on Ethereum, a big number of L2 projects are still being launched. This may be because L2 projects have the advantage of performing computations more quickly while still benefitting from Ethereum's high level of security. In the past, we have been focusing on some of the more well-known Rollup projects. This time, we will also discuss some of the more obscure projects that have been released in recent times. Scroll is the first project to be presented.<h2>zkEVM overview</h2>Why is it that optimistic rollups are receiving a considerably greater amount of attention in the present market than zero-knowledge rollups? There may be a variety of reasons for this, but by far, the most important one is that it may be used for a variety of purposes. In the case of optimistic rollups, it is not technically difficult to establish a computing environment similar to an EVM since it operates under the assumption that all transactions in L2 are genuine and then employs fraud proofs to assess whether or not the transactions are valid. As a result, the code that is now being utilized in the Ethereum network could be quickly uploaded on top of the optimistic rollup networks, the deployment of a variety of different dApps could be readily accomplished, and the ecosystem could significantly expand.On the other hand, building an EVM environment in a zero-knowledge rollup, which uses zero-knowledge proofs (ZKPs) to validate the validity of a computation, is very challenging. It is important to convert a particular calculation to the form of a QAP, which stands for "Quadratic Arithmetic Program," in order to construct a zero-knowledge proof for that computation. Constructing an algebraic circuit that is comprised of logic gates is the first stage in the process of transforming a computation into a QAP. In order to construct <a href="https://www.builder.news/crypto-insights/zk-evms-904ve" alt="ZK-EVMs: The holy grails for Ethereum scaling" title="ZK-EVMs: The holy grails for Ethereum scaling" target="_blank" rel="" class="">zkEVM</a> in the same environment as EVM, the EVM execution process—or, to be more specific, the EVM execution trace—must first be set as a circuit. This will allow a zero-knowledge proof to be derived from the EVM execution process. However, in order to do this mission successfully, a significant amount of time, money, and expertise was necessary.Because of this, zk-rollup projects have only been developed for certain purposes, such as dYdX, which focuses on trading, and ImmutableX, which concentrates on NFT. It was not possible to construct general-purpose networks that could host a variety of decentralized applications (DApps) due to technological challenges. When compared to optimistic rollups, zk-rollups have done badly in terms of both TVL and the number of users. This is another reason for this.<img src="https://cdn.builder.news/news/11ee04481e1af9e597b5028438497b73.jpg" alt="zkevm landscape" title="zkevm landscape" width="600" height="327" class="lykafe0">Source: ImmutableHowever, as Vitalik Buterin pointed out, zero-knowledge rollups may be a preferable solution to optimistic rollups in the medium and long run. Various teams have been attempting to construct general-purpose zk-rollup networks, and this is something that is currently being worked on. These projects may be categorized according to whether or not they are compatible with EVM. The first option is using Starknet and zkSync, both of which are compatible with the language they use. These two projects do not make use of EVM because, as was said before, it is exceedingly difficult to develop zkEVM from the ground up. Instead, they make use of their own proprietary virtual machines. It is possible to utilize Solidity. However, EVM compatibility is the lowest possible since there is a process of transpiring Solidity to a zero-knowledge-friendly language instead than immediately putting it into the compiler. This makes EVM compatibility with Solidity the least desirable. However, since the opcode and the execution environment both support zero-knowledge, it offers the most potential for improvement in terms of speed.The second virtual machine is the Polygon zkEVM, which is compatible at the level of the bytecode. Using a bespoke virtual machine is equivalent to the previous two projects in every way. To assure compatibility with Ethereum, however, it matches the opcodes used in the EVM with the zero-knowledge-friendly opcodes used in zkASM. This matches not only improves efficiency but also ensures compatibility with Ethereum. Even at this early level, it is possible to term it Ethereum-compatible; nonetheless, it is not yet EVM-equivalent.The third one is called Scroll, and it intends to construct a native zkEVM. Scroll is not focusing on directly building zkEVM at this time since doing so would be very challenging. At the moment, it is in a condition that is quite similar to that of Polygon zkEVM; nevertheless, Scroll does want to construct zkEVM as a long-term objective and is developing the platform appropriately. Scroll has the greatest degree of Ethereum compatibility, but it has the worst performance. This is due to the fact that the process of establishing the circuit involves a significant amount of overhead, which requires extra computational resources. Let's take a more in-depth look at Scroll, shall we?<h2>Scroll comes in</h2>Scroll is an open-source zk-rollup project that is working toward the goal of becoming an EVM-compatible zkEVM. An environment that is EVM-equivalent goes one step further than EVM-compatible by ensuring that it operates in the same manner as the requirements outlined in the Ethereum Yellow Paper. In order to accomplish this goal, Scroll is working along with the Privacy and Scaling Explorations (PSE) group of the Ethereum Foundation. Not only can Solidity be used for the creation of smart contracts in an environment that is analogous to an EVM, but a wide variety of additional tools, such as Etherscan, Foundry, Hard Hat, and Metamask, may also be utilized in the Ethereum network with little to no friction. Building a zkEVM that is similar to EVM is very challenging due to the fact that it calls for the maximum degree of Ethereum compatibility possible. Is it really feasible to complete this project?Because a significant amount of research has been carried out on the subject of zero-knowledge proofs over the course of the previous two years, the concept of developing a zkEVM has become more concrete. To begin, there is the possibility of making use of polynomial commitment. One of the ways that a particular polynomial may be condensed into a commitment value is via the use of the polynomial commitment. The KZG polynomial commitment is the technique that is used by Scroll. Other methods of polynomial commitment, such as IPA and FRI, are also available. The calculation performed on a zk-rollup may be transformed into a two-dimensional matrix by a procedure known as witness generation. This matrix can then be transformed into a list of polynomials, as seen in the picture that is located above this one. To ensure that the operation is carried out correctly, we need to check that the given polynomials fulfill the requirements of the given conditions, such as the fact that a(x)*b(x)-c(x)=0. By using the KZG polynomial commitment, it is simple to verify whether or not a certain condition (such as an (s)*b(s)-c(s)=0) is met for a particular random number "s," which helps to reduce the amount of overhead involved in establishing the circuit. In addition, with the introduction of Halo in the year 2019, it is now very simple to produce recursive proofs. When creating ZKP, hardware acceleration is achievable using GPUs, FPGAs, and ASICs; this brings the concept of developing a zkEVM one step closer to being a reality.<h2>Scroll architecture</h2>Now, let's have a look at the structure of the network that Scroll zk-rollup uses. The Scroll Network may be broken down into three primary components: 1) Scroll Node, 2) Roller Network, and 3) Rollup and Bridge Contracts. 3) Rollup and Bridge Contracts.<img src="https://cdn.builder.news/news/11ee04481e1b05e097b5028438497b73.jpg" alt="scroll architecture" title="scroll architecture" width="600" height="384" class="lykafe1">Source: Scroll<h3>Scroll node</h3>The Scroll node is responsible for collecting transactions from users in order to generate blocks of the Rollup network, submitting the blocks that it has built to Ethereum, and playing a part in the messaging that occurs between Ethereum and Rollup. A sequencer, a coordinator, and a relay are the three components that make up a Scroll node. Their respective functions are as follows:The Sequencer is a component that makes use of a Geth-forked client, which is responsible for receiving transactions from users, composing blocks, and executing them.The Coordinator is responsible for determining when a new block has been generated, obtaining the execution trace of the block from the Sequencer, and choosing a roller at random from the Roller Network to transmit the execution trace. Through taking in the execution trail, the roller assumes responsibility for the generation of ZKP.Detects deposit and withdrawal events in the bridge contract when users transfer funds, plays a role in continuously observing bridges and rollup contracts that exist in both the Scroll network and the Ethereum network, monitors whether rollup blocks and validation proofs are being submitted to Ethereum, and plays a role in determining whether rollup blocks are being submitted to Ethereum.<h3>A network of rollers</h3>The roller network is a network that is made up of rollers, each of which acts as a prover to create ZKPs. To generate ZKPs, rollers make use of specialized computing gear like GPUs, FPGAs, and ASICs. The roller is responsible for generating ZKP for each zkEVM circuit after receiving the execution trace from the Coordinator in the Scroll node, converting it into a circuit witness, and then generating the ZKP. A block proof is a representation of the validity of one block, and it is created by combining the ZKPs that have been formed by an aggregation circuit.<h3>Rollup and Bridge Contract</h3>The sequencer sends a block and state roots that summarize the current status of the scroll network to the Rollup contract. The Rollup contract then saves the state roots in the state of Ethereum and the block data in the form of calldata. In addition to this, it plays a part in the process of confirming the validation that is obtained from the rollers. The bridge contract is the one that is in charge of the transfer of funds from Ethereum to Scroll, and the relayer that is present in the scroll node is the one that watches over the deposit and withdrawal events that take place in the bridge contract.<img src="https://cdn.builder.news/news/11ee04481e1b0a8a97b5028438497b73.jpg" alt="scroll roller network" title="scroll roller network" width="600" height="391" class="lykafe2">Source: ScrollThe combination of the role groups and processes that have been discussed up to this point results in the formation of the structure that was displayed in the preceding illustration. The execution traces T for the blocks that are continually produced by the sequencer are transmitted to the coordinator. The sequencer continues to produce new blocks. In addition, the data from the block that has the hash value D is transmitted to the Rollup contract that is already part of the Ethereum network. The coordinator picks a roller at random from the roller network that is not tied to any other rollers and sends that roller along with the value T. The ZKP for T is produced by the roller that was selected, which is denoted by P. Another benefit of the approach is that it has the ability to be scaled up, which is made possible by the fact that each roller can handle it simultaneously. This is one of the advantages of the procedure. P is sent to the coordinator after it has been generated, and the coordinator then gathers P at predetermined intervals and sends it to another roller in order to construct A, which is a summary of the information that has been gathered. At this stage, the coordinator has acquired A and has transmitted it to the Rollup contract that was pre-existing in Ethereum. After that, the Rollup contract validated it, and it was given permission to grant finality to the block that it belongs to.When a block is created, finality is achieved by the completion of a series of procedures; thus, the state of the block is different depending on which process it is positioned in. These processes include the following, among others:When a block has been proposed by the sequencer, and T has been passed on to the roller, we say that the block is at the pre-committed stage. Precommitment refers to the fact that the block has been committed. The block has not yet been transmitted to Ethereum, and as long as the sequencer is reliable, it is possible to use the block in the Precommitted state despite the fact that it is now in the state it will be in when it is sent. There has been no transmission of the block to Ethereum as of yet.Committed is the state that occurs when the data of the block is transferred to the Rollup contract that is already existent in Ethereum. This happens when the block is said to have "committed" its data. This shows that the data for the block is now accessible on the Ethereum network; however, the validity of the action cannot be guaranteed because the validation has not yet been certified. Despite this, the data for the block is now accessible on the Ethereum network.Finalized is the state that is reached after all of the processes stated in the prior section has been carried out in their entirety and have been validated on the Ethereum network up to A, which stands for the aggregated ZKP. This state is referred to as the state of being "finalized." Because of the usage of the Ethereum network to verify that the operation was carried out correctly, the state in issue is now one that can be depended upon by everyone without the chance of experiencing any adverse effects.<h2>Decentralization</h2>Because rollup networks are able to verify the legitimacy of transactions in the Ethereum network through the use of fraud or validity proofs, there would not be any major concerns even if the organizations that create blocks were centralized. This is because rollup networks have the capacity to demonstrate the legitimacy of transactions. It would be desirable to decentralize it in the end, despite the fact that there are only a few obstacles, such as censorship and MEV. On the other hand. In addition, Scroll plans to decentralize not just the duty of the sequencer but also the function of the roller. Decentralizing rollers, which enables them to undertake ZKP generation in parallel and is one of the key contributors to raising the network's scalability, as we saw before in this discussion, is one of the primary ways to increase the network's capacity to support more users. The Scroll team hopes to begin by designing a solution that takes use of GPU, and then plans to put the code into the open-source community so that anybody can easily join as a roller. This will let anybody participate in the process. To take things one step further, it plans to build ASIC and FPGA solutions in collaboration with other companies that are experts in the hardware industry.<h2>Future developments</h2>At this point in time, the development of Scroll has progressed to the pre-alpha testnet stage. Because everyone on the pre-alpha testnet is able to receive testnet tokens through Faucet and test out a basic bridge and swap, we do urge readers who are interested in giving it a try. This is because everyone on the pre-alpha testnet has access to these features. The following step, which will occur before the introduction of the zkEVM mainnet, will be the alpha testnet stage, which will come after the pre-alpha testnet stage. The decentralization of the prover and sequencer that was described before is anticipated to take place after the deployment of the mainnet.Some bottom linesSeveral projects, including Starknet, zkSync, and Scroll, are working towards constructing general-purpose zk-rollup networks. Scroll is an open-source zk-rollup project aiming to become an EVM-compatible zkEVM. While building a zkEVM is challenging, advancements in zero-knowledge proofs, such as polynomial commitment and Halo, have made the concept more feasible. Decentralization is a key focus for Scroll, with plans to decentralize not only the sequencer but also the roller functions, enhancing scalability and network capacity. The project aims to involve the open-source community and collaborate with hardware experts to develop GPU, ASIC, and FPGA solutions.There is currently nothing accessible on the mainnet; however, a number of projects, such as Starknet, zkSync, Polygon, and Scroll, have declared that they will be developing zkVM and zkEVM in the near future. Despite this, the competition is getting more and more severe with each passing day. Due to the fact that Scroll is working on achieving the highest degree of EVM compatibility that is technically achievable, it is possible that the project's full product will be released after the other three. Having said that, considering that you will be able to harness the code, tools, and infrastructure that are used in Ethereum, it is worthwhile to keep an eye out for it when it becomes available. Scroll is really a thing to look forward to.<div class="pr-block-special">Disclaimer: This article is intended for and only to be used for reference purposes only. No such information provided constitutes advice or a recommendation that any investment or trading strategy is suitable for any specific name.</div>

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Scroll: Reaching the native zkEVM Layer 2