OKLink: Make your transactions efficient and secure? Inseparable from the "zero-knowledge proof" technology

Original Author: Jason Jiang

In the evolution of blockchain technology, there are two key issues that cannot be avoided: privacy and expansion. When we searched for the "standard solutions" to these two problems, we found that they are inseparable from a technology, that is: zero-knowledge proof. What is a zero-knowledge proof? How does it solve the blockchain privacy and expansion problems?

1. What is a zero-knowledge proof?

In 1985, S.Goldwasser, S.Micali and C.Rackoff from MIT proposed zero-knowledge proof for the first time in the research paper "Knowledge Complexity of Interactive Proof Systems". This is a verification protocol for a prover to prove the correctness of its knowledge without revealing any valid information.

In order to facilitate understanding, let's give an example:

Little O owns a box with a password, and he wants to convince Little K that he knows the password without telling him the real password. How to do it?

Little O came up with a way: he asked little K to write a note that only he knew the content of in the world, and then little K put it into the opened box and locked it. Then Little O took the box away and used the password to take out the note that Little K put in the box, and gave the note to Little K the next day. During this process, Little K did not learn any information (the password of the box) that he did not know before, but he still had to believe that Little O knew the password. This verification process is zero-knowledge proof.

**In simple terms, zero-knowledge proof is to establish trust between the two parties with the minimum amount of information exchanged. Without disclosing more information, A can prove to B that something/a certain conclusion is correct. **

According to the interaction mode in the proof process, it can be divided into two categories: "interactive zero-knowledge proof" and "non-interactive zero-knowledge proof".

Interactive zero-knowledge proof means that in order to prove something, the prover needs to interact repeatedly with the verifier, just like a lie detector: the verifier constantly asks questions to challenge the authenticity of the prover’s commitment, and the prover needs to constantly Respond to these challenges until validators are convinced. Its flow is as follows:

Early zero-knowledge proofs were all interactive. This method is straightforward, but the process is lengthy and inefficient: both parties must complete the verification online at the same time, and only one verifier can be trusted at a time. If multiple people are to be trusted, the above process must be repeated. This process is tiring to think about.

Thus, non-interactive zero-knowledge proofs emerged. In non-interactive zero-knowledge proofs, the prover and the verifier agree on the verification rules in advance, the prover provides the data as promised, and the verifier can verify the correctness of the data at any time. In this kind of non-interactive verification, both parties do not need to be online at the same time, and the prover only needs to provide proof once. **The applications in actual scenarios are basically non-interactive zero-knowledge proofs, such as ZK-SNARK and ZK-STARK. **

2. What is the use of zero-knowledge proof in the blockchain world?

Zero-knowledge proofs are mainly used to solve two types of problems in the blockchain world: privacy and scalability. **

(1) Privacy

One of the important application results of zero-knowledge proof is the Zcash project launched in 2015 that can realize private transactions. In addition to anonymous coins such as Zcash, zero-knowledge proofs can also play a role in scenarios such as blockchain finance, on-chain voting, and identity verification.

In blockchain financial applications, zero-knowledge proofs allow participants to flexibly choose which transactions and information they want to disclose and hide. For example, companies can selectively expose certain payments for audit trails, while hiding confidential information about confidential customers, employee salaries, contractors, suppliers, and more.

When voting on the chain, zero-knowledge proof can also allow participants to vote anonymously and verify the validity of the voting results.

In addition, zero-knowledge proof can also help users achieve identity verification without revealing specific identity information. Polygan ID on Ethereum adopts a zero-knowledge proof verification scheme, which not only helps users protect privacy, but also meets regulatory requirements for KYC verification specifications. Users are free to choose when and which data to share.

(2) Expandability

The blockchain is in urgent need of expansion due to performance limitations that cannot meet market demand, and the ZK Rollup expansion solution based on zero-knowledge proof is regarded as the ultimate solution for Layer 2 expansion. ZK-Rollups improves the throughput of the blockchain by transferring calculations to the off-chain, that is, to pack a large number of transactions into a Rollup block, and generate a validity proof based on zero-knowledge proof under the chain. Smart contracts on Layer 1 only need Validating the proof allows the new state to be applied directly, resulting in lower gas and higher security.

zkSync based on ZK-SNARKs technology and StarkNet based on zk-STARKs technology are currently the most representative ZK-Rollups projects.

Among them, zkSync is a Layer 2 expansion solution launched by Matter Labs in 2018, which improves the scalability of the Ethereum network by using Rollup based on zero-knowledge proof. **In February of this year, zkSync announced that the zkSync Era main network was officially launched. OKLink multi-chain browser later took the lead in accessing zkSync main network data, becoming the first multi-chain browser supporting the zkSync network in the entire network. **

StarkNet is a permission-free Layer 2 network developed by the Israeli software company StarkWare. By using zk-STARKs technology, it can help DApps achieve greater computing scale at lower transaction costs. Since the launch of the mainnet in November 2021, the StarkNet ecosystem has developed rapidly. There are currently more than 100 Dapps and services, covering different categories such as DeFi, NFT, wallets, and cross-chain bridges. As one of the projects with the highest valuation and the largest market share in the ZK Rollup track, the development of StarkNet has attracted much attention. The OKLink multi-chain browser of OKLink will also launch the StarkNet browser in the near future, providing more comprehensive and richer on-chain data insights and services for all users who pay attention to and participate in the StarkNet ecology and Layer 2 construction.

It is reported that the StarkNet browser will be the 30th blockchain browser launched by OKLink and the second ZK Rollup browser after zksync. In the future, the OKLink multi-chain browser will also launch blockchain browsers for well-known ZK Rollup projects such as Polygon-zk, Linea, Base, and Scoll based on zero-knowledge proofs.