This article is from the WeChat public account: Silicon Valley insight (guigudiyixian) , author: Juny, the original title: “block chain again” meteoric rise “zero-knowledge proof Why has technology become the focus of Silicon Valley blockchain research? 》 Picture from: Visual China

The concept of blockchain has been around for 10 years since Bitcoin was introduced in January 2009.

Even so, what is the blockchain and what can it bring? Many people still see flowers in the fog, seemingly understand. Coupled with the hype of various virtual currencies in recent years, most people pay attention to this complicated new thing.

In October, China officially announced that “Blockchain is an important breakthrough in independent innovation of core technology”, which has made the topic of the long-awaited blockchain in China once again rocketed at a rocket-like speed, setting off a new wave of technology and applications. Research boom. As one of the most important underlying technologies of the new blockchain, zero-knowledge proof has also become the focus of current research in academia and industry.

In order to explore the development of the latest blockchain technology, Silicon Valley Insight went to the annual San Francisco Blockchain Summit and interviewed one of the speakers of this conference, the Bulletproofs theoretical invention from Stanford University. People Benedikt Bünz, together discussed the connotation of zero-knowledge proof technology and its significance for the development of blockchain.


Benedikt Bünz

Benedikt Bünz, Ph.D., Applied Crypto Group, Stanford University, and author of Bulletproofs theory. Chief scientist and co-founder of startup Findora.

What is zero-knowledge proof?

Benedikt said that the essence of blockchain is actually cryptography, and the concept of blockchain came into being after the advent of Bitcoin in 2009. As one of the three basics of modern cryptography, zero-knowledge proof technology was proposed by MIT professors ShafiGoldwasser, Silvio Micali, and cryptographer Charles Rackoff as early as 1985. For their pioneering contributions in modern cryptography and zero-knowledge proofs, in 2012 Shafi Goldwasser and Silvio Micali also won the Turing Award, known as the “Nobel Prize in Computer Science.”

Therefore, zero-knowledge proofs existed before the blockchain, and have already reached a very high theoretical level. However, the early zero-knowledge proof theory did not have a good application scenario, only staying at the theoretical level. It wasn’t until the advent of the blockchain that it created opportunities for zero-knowledge proof.

Simply speaking, zero-knowledge proof is that the prover knows the answer to the question, he needs to prove to the verifier the fact that he knows the answer, but requires the verifier not to get any information about the answer.

Does it sound dizzy? Never mind, give you a simple example.

You and your companion have a room in front of you, and there is a password lock on the door. You need to prove to your companion that you know the password of the lock, but you do n’t want to tell him what the password is. So what should I do? ? Your partner knows that there is a book in the room where he wrote his name, and you just need to show it to him to prove that you can enter the room.

In the process, you (Certifier) ​​ doesn’t need to tell your companions directly (Verifier) ​​ What is the password of the room, but this book with his name shows him the fact that you know the password.

What is the relationship between zero-knowledge proof technology and blockchain?

The concept is not difficult to understand, but why is it that zero-knowledge proof is important for the next development of blockchain?

Let’s first briefly understand the principle of Bitcoin trading.

Suppose A wants to transfer a bitcoin to B. At this time, we consider bitcoin as a check, and A wants to transfer this check to B, then he needs to create a new check for B, and B’s face tears up his original check. In this process, the transaction addresses of the two must be related. So what are the consequences of this?

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Benedikt explained to Xiao Tan that the anonymity of Bitcoin is only reflected in the fact that the address does not have a real person identity, but all transaction information is completely public. So once someone knows your Bitcoin address, (such as himTransfer to you) , he can check all your transaction history and balance from the chain. And this kind of privacy exposure will lay a deep hidden danger for large-scale commercial applications in the future.

It is for this reason that zero-knowledge proof technology is particularly important. What changes can it make?

Take Zcash, the first application of zero-knowledge proof technology to digital currency, as an example, it is still A to ZCash to B.

Unlike Bitcoin, A’s voucher will have a series of voucher numbers. When A is transferred to B, A does not need to exchange addresses directly with B. Instead, it has a third-party voucher invalidation list. By entering the “invoice code” of A, which needs to be abolished, and using “remarks to be abolished”, it is proved that Alice’s check has become invalid, and then B will obtain a new valid voucher number. In this way, B does not need to see A’s certificate, but still realizes the transfer of asset ownership.

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There are two main issues involved in this zero-knowledge proof, one is who is doing this trusted third party (trusted set-up), and the other is proving whether the performance is good enough (verification time & proof size) . Therefore, many scholars have begun to study different solutions for these two dimensions. Some have focused on solving performance problems, such as Libra (Not Facebook’s libra) , etc., some of them are to solve the problem of eliminating” trusted third parties “, such as Bulletproof proposed by Benedikt and Supe he is optimizingss = “lazyImg” _src = “ imageView2 / 2 / w / 1000 / format / jpg / interlace / 1 / q / 85” data-w = “899” data-h = “499”>

Pictures are from the official Findora website

The reason for doing this project is that they believe that the current maturity of zero-knowledge proof technology has developed to a stage where it can be commercialized. At the same time, the development of the financial industry, especially the development of digital currency, will have a significant effect on zero-knowledge proof Strong technical requirements.

Why is there such a demand?

First, let’s take a look at the three main payment methods currently on the market. The first is a completely decentralized chain of FacebookLibra, Ethereum, Bitcoin, etc. that can be used for payment. The second is a centralized Alipay, WeChat payment, and bank transfer. The third is the privacy protection ZCash, Monero, Findora and other payment networks.

These three payment methods, decentralized Libra, Ethereum, and Bitcoin are highly transparent to the public, but the privacy is the worst; traditional third-party giants’ centralized institutions are only used by third parties for transaction information. It is known that it belongs to the medium of privacy; and the untraceable privacy payment using zero knowledge proof technology has the highest privacy.

Obviously, most users will definitely not want their property transaction amounts to be seen or tracked by everyone, so there is a need for privacy.

In addition to currency payments, in financial applications such as hedge funds, exchanges, and P2P, not only privacy is required, but also complex compliance is required, which requires financial networks to support very complex At the same time of the transaction, it can also ensure a high degree of privacy and efficiency, and may also ensure the auditability of the transaction, in order to gain considerable trust from customers.

And this is what the Findora project wants to do. It uses zero-knowledge proof technology to build a financial platform that supports complex transactions and also has high privacy, efficiency, and auditability.

For example, in investment fund management, current funds are able to see which investors have subscribed for how many shares of the fund, but with zero-knowledge proof technology,Fund managers only know the overall fund size, but they don’t know exactly how much money each investor has.

In addition, they have developed several zero-knowledge proof tools. Some can be used for privacy protection calculations, and have a great role in helping to seal bid auctions, dark pool transactions, fair lottery, etc. There are also tools for demonstrating compliance that financial institutions can use to prove compliance while protecting privacy.

Benedikt said that the current Supersonic technology they developed for Findora is the first SNARK that does not require trusted settings, and the size of the proof is very small, such as: 1 million gates with high complexity, and only 10 proofs are needed. -20KB. This further guarantees the computational complexity, credibility and verification speed.

Benedikt shares technology at the conference

What other difficulties do blockchains need to break through?

In addition to the privacy issues solved by zero-knowledge proofs, Benedikt told the small investigator that he believes that transaction efficiency and energy consumption are two other issues that need to be addressed during the development of blockchain technology.

Blockchain has achieved decentralization and security, but increasing transaction speed has become a problem. Take bitcoin as an example, bitcoin currently supports a maximum of 7, 8 transactions per second, but in traditional payments, visa can support a transaction volume of 3,000 transactions per second. Obviously, if the blockchain is to develop on a large scale, the increase in transaction speed is an obstacle that must be overcome.

In addition, the issue of energy consumption is urgently needed to be solved. Bitcoin available in 10 years, as prices continue to break new highs, the total energy consumption Bitcoin network has continued to grow at an alarming rate. According to the latest report released by the Cambridge University Research Institute, the entire Bitcoin network