TL;DR:

• Zero-Knowledge Rollups (ZK Rollups) are a Layer-2 solution for blockchain scalability.

• zkSync uses zk-rollups for Ethereum's layer-two blockchain, with gas fees 1/100 of L1 gas and reportedly supporting over 100,000 transactions per second.
• Polygon zkEVM uses zero-knowledge proofs to reduce transaction costs and increase throughput while inheriting Ethereum's security, with a lower throughput of 2,000 TPS.
• ZkBNB can package hundreds of transactions and generate cryptographic proofs as zkRollups, allowing users to trade digital assets without permission and offering developers the opportunity to build marketplaces for NFTs.
• The three zk solutions are developer-friendly, allowing easy porting of Ethereum dApps.

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Zk Rollup: Layer-2 Solutions for Blockchain Scalability

Blockchain technology has come a long way in recent years, but one problem still looms large: scalability. As the number of users and transactions continues to increase, the limitations of blockchain become more apparent. That's where Layer-2 solutions like Zero-Knowledge Rollups (ZK Rollups) come in. ZK Rollups are considered the ultimate Layer-2 solution for blockchain-related scalability problems, and they can potentially transform the way we use blockchain technology. In this article, we'll take a closer look at the innovations in the zk-rollup space, focusing on three main players: zkSync Era, zk-BNB, and zk-Polygon. 

What is zkSync:

The zkSync blockchain uses zk-rollups as a scaling technology for Ethereum's layer-two blockchain. In a similar fashion to optimistic rollups, zk-rollups gather transactions off the Ethereum mainnet and submit their proofs to Ethereum. By doing this, hundreds of transactions are batched into one, verified and secured by Ethereum.

With zkSync, each batch of transactions is passed to an off-chain provision that generates cryptographic proof (called a SNARK) that they are valid. Verifying the validity of the proof is easier than developing the proof. The ease of this process means that it can be sent to Layer 1 and confirmed in a smart contract. As a result, transfers between Layers 1 and 2 are near-frictionless.

Furthermore, since it is EVM compatible, you can easily transfer existing Layer 1 smart contracts to Layer 2.

Moreover, zkSync with its V2 version it can reportedly support over 100,000 transactions per second once ETH2 data sharding is available. According to zkSync, gas fees are 1/100 of L1 gas and cheaper than optimistic rollups.

Further, the main Ethereum blockchain secures the assets, and you can move your assets back to L1 at any time.

What is Polygon ZkEVM: 

The Polygon zkEVM takes advantage of zero-knowledge proofs' scaling power. In fact, it's the first zero-knowledge scaling solution that is entirely equivalent to an EVM. 

zkEVM uses ZK proofs to reduce transaction costs and increase throughput while inheriting Ethereum's security. Polygon zkEVM has a lower throughput of 2,000 TPS.

Further Polygon zkEVM makes transactions much more efficient by creating a parallel chain to the main Polygon network using zk-proofs. It allows transactions to be validated without exposing sensitive information, making them faster and more secure.

Moreover, Polygon zkEVM allows developers and users to use the same code, apps, and tooling but reportedly with much better performance and lower fees. By leveraging Ethereum's network effects, EMV-compatible zkEVMs can benefit from EMV's benefits. 

The zkEVM allows users to deposit assets from Ethereum and transact off-chain. All of these transactions are grouped into batches, and a zero-knowledge proof confirms each transaction's validity. By doing this, the operators of zkEVM cannot steal user funds. 

Additionally, it allows smart contracts on L2 to perform transactions that can be verified on L1 without the need for nodes to re-execute them.

What is ZkBNB:

The ZkBNB has the same capability of packaging (or "rolling-up") hundreds of transactions and generating cryptographic proofs as zkRollups. It is possible to prove the validity of each transaction in the Rollup Block using SNARKs (succinct non-interactive arguments of knowledge). In this way, it ensures that all funds are held on the BSC, while computations and storage are performed on the BNB Sidechains, at a much lower cost and more quickly. 

According to the protocol, ZkBNB is just as secure as BNB Smart Chain because it uses zk-SNARK proofs.

Furthermore, zkBNB's built-in liquidity pools allow users to trade digital assets without permission. zkBNB also offers developers the opportunity to build marketplaces for crypto collectibles and non-fungible tokens (NFTs).

In addition to supporting 100 million addresses, zkBNB can reportedly handle up to 10 thousand transactions per second (TPS), and gas fees can be reduced by up to 10x. Moreover, if a user feels that his transactions are censored by zkBNB, they can withdraw funds at any time.

Similarities and Differences

ZK-rollup has several advantages over other scaling solutions, such as Sidechains and Plasma.

• Rollup validators cannot tamper with the states or embezzle money.
• It is also possible for users to retrieve their funds from the Rollup even if the validators stop cooperating. Due to the readily available data, it is easier to access than in Plasma.

• Validity proofs eliminate the need for users or other trusted parties to monitor Rollup blocks online.

The three zk solutions discussed here are developer-friendly, allowing easy porting of Ethereum dApps. 

In spite of the similarities between these projects, there is one critical difference that sets zkSync apart. In contrast to Polygon's zkEVM and zk-BNB, zkSync does not support bytecode. With bytecode compatibility, Ethereum's core code can be easily ported to Layer 2 networks with minimal changes.

As well, zkSync requires projects to be compiled using its LLVM-based compiler before they can be used on its network. Due to this approach, zkSync differs slightly from the other two zk solutions.

Since zkSync Era launched, the project has accumulated a total value locked (TVL) of $249 million, according to L2 Beat. It is significantly higher than the $8.4 million on Polygon's chain of zkEVM. This discrepancy can attributed to the airdrop hype around zkSync Era. 

Zero-knowledge proofs allow individuals to verify their identities without divulging sensitive personal information. As an alternative to providing identity details, users can simply verify that they meet specific criteria, such as a decentralized identity that verifies their citizenship without sharing their name or passport number. 

Even though all current zk solutions offer several advantages for the crypto space, it will take time to see which one wins since the technology is still relatively new and many innovations have yet to be implemented.