Zero knowledge proofs (ZKP) are a category of cryptographic primitives that enable something seemingly impossible: proving that one party knows something, without ever revealing the information itself. For example, a simple ZKP allows you to prove that you know a particular password without actually revealing it.
The first implementation of ZKPs to gain major traction was Zcash, the popular privacy coin. Through its Groth16 Zk-Snark algorithm, it allowed people to transact with full privacy. The cryptography allowed to essentially encrypt transactions, while using ZKPs to ensure they followed all the relevant rules (such as not sending more coins than the user owned, or not creating additional coins).
Since then, zero knowledge technology made great strides and expanded its list of use cases. It isn’t just about privacy: ZKPs are used to scale blockchains, ensure verifiability of data, prove uniqueness of digital identities and many more. Here are a few of the most interesting projects that are working on bringing the next generation of zero knowledge proofs:
#1 ZkSync Era’s PLONK for scalability
ZkSync Era is a layer-2 rollup that helps scale Ethereum by using the power of ZKPs. The Era blockchain provides batched ZK proofs of each state transition of its EVM-compatible network, which can be verified directly by Ethereum smart contracts. This saves a tremendous amount of space and computing power, as a single proof can include thousands of transactions while occupying very little space. ZkSync Era leverages the “succinctness” of ZKPs — not only does the proof not need to include the data itself, but it can also be many times smaller than what it’s representing. As one of the first live examples of this scalability technology, ZkSync Era is extremely promising for letting blockchains handle mainstream levels of usage.
The specific proof used for zkSync Era is called PLONK — an ultra-efficient proving system that’s been around for a few years.
#2 Space and Time’s Proof-of-SQL for tamper proof data
Space and Time is a decentralized data warehouse, essentially a next-generation platform for easily storing and using data in a database, including blockchains. It’s backed by a unique system called Proof of SQL, which uses ZKPs to ensure that the data you store and retrieve remains tamper-proof, correct and up to date.
Proof of SQL uses a verifier and prover system to write and read from Space and Time data warehouses, meaning that each operation is backed by provable ZKP-based cryptography.
Space and Time is unique among all its peers, who tend to use economic incentives to ensure the data they deliver is correct. But this approach isn’t quite as sturdy as a zero knowledge proof, giving Space and Time an edge. The technology also allows introducing several key innovations, such as the ability to read historical blockchain data directly from smart contracts, a first in the industry.
#3 Anoma’s Unique Intent-Based Private Blockchain
Anoma is a novel blockchain protocol aiming to develop a new way of using blockchains for economic transactions. It relies on the concept of an intent, which is a “partial transaction” that expresses a cryptographically verifiable intention to do something. The easiest example in a crypto setting is that of a limit order on an exchange: you’re committing to buying or selling an asset for a certain price, and the full transaction will only execute if somebody comes in to take your order. Anoma generalizes this structure for all kinds of economic activity, which is very unique in blockchain, where all transactions usually execute fully or not at all.
Zero knowledge proofs are everywhere in Anoma. For example, they underpin Taiga, a zero knowledge program execution protocol that allows applications to have their logic completely shielded from outside eyes by hiding its type, its data and the parties involved.
It uses the Halo2 zero knowledge proving system to hide all relevant transaction data, which was first proposed by the developers of Zcash.
Taiga relies on custom Validity Predicates: a way to express application rules and ensure that a program follows them, without forcing it to reveal any of its critical data. Taiga is a radically different way to execute blockchain applications, using intents and “notes” to express business logic, promising to be both private and much more expressive than regular smart contracts.
#4 Aztec’s private and scalable Rollup
Aztec is a hybrid layer-2 zkRollup that supports both public and private smart contract execution. Like zkSync, it improves the capacity of the Ethereum blockchain and connects to it like any other rollup. But unlike “simple” zkRollups, Aztec also makes a point in enabling fully private transactions.
Privacy in blockchains is a hotly debated topic, but in many ways it will be necessary: businesses and regular people are all accustomed to a certain level of privacy in the traditional financial world. Corporations can’t trace their competitors’ entire budget, you can’t see your friend’s expenses, and many would agree that this is how it all should be. With traditional blockchains, this is generally impossible to guarantee.
Aztec’s been building its private rollup for several years, and it has spearheaded ZK technology tremendously through its R&D. Once ready, it promises to be a revolutionary blockchain platform where both public and private smart contracts coexist.
#5 Verifiable Decentralized Identities with Polygon ID
Proving your identity online is not an easy task, especially in Web3. Many applications need to know who their customers are — maybe not at an individual level, but at least to be certain that each of their users is one unique human.
Traditional document-based verification relying on centralized stores of data are often leaked and hacked. And even if they aren’t, users are often uneasy to provide their personal data to random people and companies online.
This is where Decentralized Identifiers (DID) based on ZKPs can shine. They enable a new world of digital identity where consumers of the data can verify a user’s uniqueness without ever knowing who they are. DIDs can be created both in a decentralized and centralized setting, depending on the application. But the verification system means that you can port your identity across all platforms — avoiding, for example, having to go through KYC with each new financial platform you’re using.
An application of DIDs being developed is Polygon ID, which is an infrastructure layer for enabling ZKP-based identifiers. Through a series of partners, users can create onchain representations of their identity, which can then be easily verified by other consumers of the data, without ever having to know the person’s identity.
This might be the most important use case for ZKPs yet — in the modern world, personal privacy is getting ever more eroded. This novel cryptography can offer the best of both worlds of preserving privacy, while hindering illegal uses of anonymity.