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Why is zkSNARKs so important in the Web3.0 era to implement new identity primitives?

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The zero-knowledge nature of zkSNARKs allows participants to make very broad and complex trusted claims.

原文标题：《 ZK Identity: Why and How (Part 1) 》

Original author: 0xPARC

xinyang@DAOrayaki.org

This article is the first in a series on why advances in cryptography are important for implementing new identity primitives. "Why" is covered in this article; The next article will explain how.

The design of online identity systems has been the subject of intense debate over the past few years. Modern digital identity systems have enabled new and complex online interactions and communities. Unfortunately, many of these systems also have significant weaknesses.

Many of these weaknesses can be attributed to the limitations inherent in the design of centralized identity systems. First, these systems are usually built around a central control point, and therefore a central point of failure. Modern e-commerce, social media and messaging platforms are vulnerable to pressure or interference from powerful actors, such as authoritarian governments, or to technical attacks by malicious hackers; When the central operator is coerced or hacked, other parties besides the central operator will also be at risk. Second, these systems depends on the concentration of power in the hands of carriers, they could not have exactly the same as that of all users (financial, moral or social) -- for example, have diverse global audience private social media companies must decide what is often unreasonable conduct review, what is the interest of public safety behavior, Although they often do not have the proper capacity to make judgments.

Decentralization and encryption mechanisms are not magic panacea, but they do provide some useful tools, and they expand the design space for digital identity systems. As more of our social and economic lives move online, it will become increasingly important to design identity systems that are secure, secure and controlled by users. In this article, we will argue that new encryption primitives, such as zkSNARKs, are critical to building identity systems with these features.

At their core, zkSNARKs are useful because they enable users of digital systems to generate arbitrarily complex trusted claims without relying on trusted parties. All identity systems are built around some mechanism for producing a credible identity and reputation claim -- usually a fairly complex claim attached to a credential from a trusted authority such as a government or company. By applying the zkSNARK structure to claims about identity and reputation, we can reinvent digital identity systems and put control and data custody in the hands of users.

A credible claim

Since zkSNARKs operates on precise, mathematically defined "claims," we must first precisely decompose the nature of the claims involved in the identity system.

It's hard to do business with a completely unknown and distrustful counterparty. Common sense suggests that as trust between counterparties decreases, so does the likelihood of co-operation; Game theory tells us that in a one-off prisoner's dilemma, the best strategy is always to defect. You'd much rather buy a used car from a close friend who's connected to your social network than from an untrustworthy 58.com seller from out of town who won't even tell you his name.

To build trust with each other, we need to be able to make credible claims: statements about our identity and reputation that are credible to the people we interact with. If the 58.com seller above assures you that he has "sold a lot of cars before and everyone loves my car, trust me," that's not really a credible statement. But that claim feels more believable when combined with five-star reviews you know from verified buyers on a popular website.

The idea of trusted claims sounds obvious, but setting up a mechanism to produce them (in this case, a popular classified-site) and making them legal is not easy. In the traditional model, our usual solution is to delegate record management to a trusted authority so that they can prove our claims about identity and reputation and give them credibility. This institution must demonstrate their legitimacy and credibility over time, often in adversarial environments, and maintain the infrastructure for mass generation and distribution of certificates.

Crucially, in most models, proof of the central authority is what makes the claim credible. It's a valid government ID, so I'm a citizen; This is an accurate list of my followers, so I'm a social influencer; These are a set of verified reviews and ratings, so I'm a trusted online retail business.

Another application for trusted declarations is further down the stack. First of all, how do you know that the person or business you're interacting with is making a statement to you about themselves, and not someone else? Many systems rely on trusted institutions that perform more basic functions than proof of identity itself. An API access token, a government-issued passport, or a signature chain generated by a certificate authority when you visit a website are proof of an identity claim.

Useful identity systems allow participants to make very broad and complex trusted claims.

(digitally) Doordash Web servers make trusted claims to you when you order through Doordash (" I'm Doordash Web Server, "via a cascade of DNS signatures); You make a trusted declaration of your identity to Doordash through a third-party identity provider (" I am a Doordash user and should be allowed access to the credit card saved on this account "by using" Google Login "). You make a credible statement to Doordash about future payments through various financial institutions (" I have the money to pay you for my order, which will arrive soon "through a credit card provider that doesn't reject transactions).

(Physical) When you borrow money to buy a house, you implicitly make a number of credible claims about your identity and reputation to banks, real estate agents, sellers and the government.

(Mix) When you apply for a job, you make a credible claim to your potential employer by using many different certification systems. By citing credentials (degrees, certificates) from educational institutions or professional certification bodies, references from colleagues you have worked with, and references from previous companies, you claim that you have the training and personality to do the job. Social media and other online account providers can provide further proof of implicit claims about who you are.

privacy

The situation is further complicated by the fact that almost all identity systems by nature require privacy to function as intended.

Privacy is important, sometimes controversial, for moral and ideological reasons; But more fundamentally, as a simple system design problem, it is often necessary. For example, almost all identity systems rely on the concept of secret data to generate trusted identity claims -- passwords, social security numbers, private keys, credit card passwords, account recovery questions, and so on. For obvious reasons, this data must be kept secret.

In addition, the process of producing trusted claims with fully transparent data can have negative externalities, or at least complex ones; Privacy safeguards prevent this. For example, if you have to show your entire financial history, only to buy or sell items in an online market, bank statement, credit card transactions, loan payments, and other work that he can use this information to have nothing to do with the original transaction beyond interaction (negative examples include advertisements, harassment and even blackmail). Privacy "sandboxes" provide one-time interactions that are well defined and limited in scope so that we can build more complex systems from simple and understandable building blocks.

In traditional systems that require privacy, we have to delegate more power to central authorities, which store private data and guarantee credible claims about it that are nearly impossible to verify.

The role of cryptography

All of the models we have discussed so far for trusted claim generation and identity systems involve a centralized actor. As we've discussed, there are many reasons to want a system that doesn't rely on a powerful recorder or manager.

But the obvious question is: If I don't have your data, how can I trust your story? If you send me your data, how do I know it's valid? If you want to make a claim about private data, what do we do? This is where cryptography comes in.

From our perspective, much of applied cryptography (and consensus) over the past fifty years has been a progressively expanding project of what credible claims can be made without credible authority under various resource constraints and privacy conditions.

Digital signature schemes allow me to make credible claims about the consistency of my online identity across a range of different actions by signing a series of messages with the same private key. "I'm authorized to charge Alice's credit card."

The group signature scheme allows me to make more sophisticated privacy claims about my identity. "I'm a member of the alumni group, but I'm not going to tell you which one."

Signature aggregation, multi-signature, and threshold signature schemes allow me to make statements about group behavior under a variety of resource constraints. "This large collective organization -- not just one reckless employee -- has authorized the transfer of money from our financial accounts."

Consensus schemes and programmable smart contracts allow me to make credible and irreversible commitments to future actions. "If you send me digital asset A, I will immediately send you digital asset B in exchange."

Historically, progress has been slow -- each of these cryptographic primions defines a new, scoped declaration whose structure is highly explicit. In the past few years, however, that has changed.

The exciting thing today is that thanks to SNARKs, we now have a mechanism to effectively make arbitrary credible claims. Thanks to the zero-knowledge nature of zkSNARKs, we can also tweak the declared privacy guarantees exactly to our liking.

Here are a few examples of what kind of claims you can make with zkSNARK that were previously impossible.

"I am a trustworthy debtor. I have repaid large loans to three trustworthy banks on time, although I will not disclose the banks or what the loans were for."

"I am a respected community member. Although I am writing this post anonymously, I have accumulated over 10,000 support points on this forum under my named account."

"I am a long-time crypto Token collector. The ethereum addresses I control collectively hold at least two NFT from the dark forest Valhalla series and at least 100ETH."

These declarations can be combined, composed, and even programmed in arbitrarily complex ways.

While all of this is theoretically possible, we still have a long way to go. Creating a powerful set of ZK identity tools for the next generation of applications requires substantial improvements in performance, reliability, developer experience, and application design patterns. In the next article, we will discuss our understanding of the way forward.

Addendum: What goes into identity?

To understand where cryptography can be used to build an identity system, it is useful to break down the concept of an identity system into its key components.

When analyzing a particular identity system, we can ask the following questions.

What is the atomic unit of identity?

Physical world: Identity is often related to legal personality. In other words, the atomic unit of identity is the individual, or company.

网络空间：身份可以是谷歌/脸书/推特账户；与证书机构相关的公钥/私钥对；一些基于以太坊的 Token 的持有人（可能不与具体地址挂钩！）；以及其他。

What constitutes valid proof of identity or proof? Who can issue identification? Who can revoke privileges associated with proof of identity?

Physical world: A valid proof may look like a state-issued ID card or business license. The government ultimately has the power to have the privileges that come with having a valid id: it can revoke your passport, for example.

Cyberspace: A valid proof could be an OAuth token provided by FB, or a valid digital signature (or signature chain). Various service providers have authority over various proofs: Twitter can block your account, for example.

Who keeps ancillary data related to your identity? Who has access to this data, and who controls that access?

The physical world: Secondary data is held by government agencies and bureaucracies, private service providers (banks, credit scoring agencies) and personal contacts (your personal network).

Cyberspace: In a centralized model, secondary data is held by large technology companies. In a decentralized model, secondary data is shared between client software you control (browser, personal web server) and a decentralized storage network (for example, historical transaction data or smart contract status in a blockchain).

What records, documents or certificates are signals of reputation and credibility? Who determines these signals and how to interpret them? Who has access to the basic input data that determines reputation? Who has access to these signals?

The physical world: credit score reports, background checks, social references, employment letters, certificates and honors, and titles.

Cyberspace: NFT ownership, account age and prior activity, proof of likes on the Internet, Reddit or other forums.

Some of these concepts blend: identity, reputation and proof of identity are closely related and not easily separated. In some systems, for example, the atomic unit of identity is even defined as "what the central authority can validly prove" -- the concept of a Facebook account that is not stored in a Facebook database does not exist.

In general, the identity we use in this series refers to a persistent tag for an entity (a person, an organization, a robot) and represents that entity's legal personality, public key, account ID, and so on. We use reputation to refer to statements about an entity's past behavior (" Alice always keeps her promises, "" Bob always pays his credit card bills on time," "Cozy Home always uses accurate pictures on its Airbnb listings").