It’s been a while since my previous article about ZK Proofs. It’s time to see what’s changed since then, what kind of new solutions and blockchains have been developed, and whether the idea of using zk-proofs with the blockchain still makes sense. We’re gonna do this from a new angle - the perspective of L2s! Grab a cup of coffee and lesssssssgo!

zk-Rollups: The Magic Sauce Behind Scalable Blockchains

Alright, let’s talk about zk-rollups. You might’ve heard this term thrown around in crypto circles, especially if you keep an eye on Ethereum or scaling solutions. But what’s the big deal, and why should you care? So, blockchains, especially the popular ones, are a bit like tiny city centers. Everyone wants to live there, but space is extremely limited, and rent (aka transaction fees) keep increasing. People are sending more and more transactions, firing up complex apps, and, surprise! The main chain gets congested fast. Enter zk-rollups, our scaling superheroes.

zk-rollups are basically clever ways to pack loads of transactions into one neat bundle, do most of the heavy lifting off-chain, and then prove to the main chain: “Hey, we did everything right!” using some cryptographic magic called zero-knowledge proofs (yup, that’s the “zk” part). The chain just checks the proof, saves a bit of summary data, and - boom! - we’ve got space for way more action without breaking a sweat.

Calldata, Storage, and Why zk-Proofs Are Awesome

Normally, every transaction and its data sit on the blockchain forever. It’s like keeping every grocery receipt since 2015 - messy and potentially expensive. But zk-rollups have a neat trick: they only send the superimportant stuff (called “calldata”) to the chain, while the rest of the data hangs out off-chain, compacted by zk-proofs into tiny packages. What does this mean? Well, instead of needing a truckload of space, you can fit a week’s worth of shopping into your pocket. zk-proofs let you crunch thousands of transactions into one small proof that anyone can check. This saves tons of space and makes everything run faster and cheaper. So, if you’re into scaling, zk-rollups are basically a turbo mode for blockchains.

Projects & Ecosystem: The zk-Rollup Party

A bunch of projects are already rolling (pun intended) with zk-rollups. On Ethereum, you’ve got zkSync, StarkNet, Polygon zkEVM, and more. These guys are all about making things faster, cheaper, and more user-friendly. Solana and other blockchains are also dipping their toes in, tweaking zk-tech to fit their own vibe. But, and this is a big BUT, don’t be fooled. Just because something uses zk-proofs doesn’t mean it’s private by default. Most zk-rollups are all about scalability, not privacy. So, your transaction details might still be out in the open. If you’re dreaming of total privacy, you’ll need extra tech (and maybe a different rollup flavor). zk-proofs equal speed and compression, but privacy? That’s a whole other story.

Overview of the most significant guests of the zk-Rollup Party

Fortunately, in the blockchain universe, there's enough space for many different projects, and some of them have already developed privacy-focused L2s. Let's take a look at a set of examples showcasing how zero-knowledge proofs (ZKPs) are used across different blockchains, highlighting privacy, scalability, and other unique use cases.

Privacy-Centric Blockchains

• Zcash
  - ZK usage: zk-SNARKs for shielded transactions, hiding sender, receiver, and amount.
  - Reason: Privacy.
• Aztec Network
  - ZK usage: zk-SNARKs for confidential transactions on Ethereum.
  - Reason: Privacy + scalability (private DeFi).
• Aleph Zero
  - ZK usage: zk-SNARKs for private transfers and confidential smart contracts.
  - Reason: Privacy + scalability.

Scalability-Focused Blockchains

• Polygon zkEVM
  - ZK usage: zk-SNARKs to batch, prove, and submit multiple transactions as a single proof to Ethereum.
  - Reason: Scalability (low fees, high throughput); privacy is secondary.
• StarkNet (and StarkEx)
  - ZK usage: zk-STARKs for rollup scaling, enabling thousands of transactions to be proven and submitted efficiently.
  - Reason: Scalability.
• Loopring
  - ZK usage: zk-SNARKs for high-speed, low-fee decentralized exchange via zk-rollups.
  - Reason: Scalability.
• Mina Protocol
  - ZK usage: Recursive zk-SNARKs maintain a tiny blockchain size by compressing the chain history.
  - Reason: Scalability (tiny chain, easy node sync).

Other worth mentioning, not-ZK-rollup, but still ZK, solutions

• Immutable Audit/Compliance
  - Example: Some enterprise or permissioned blockchains use ZKPs to prove compliance or data validity (e.g., KYC checks) without revealing sensitive customer data.
• Identity
  - Example: Privado ID uses zk-SNARKs to enable users to prove certain attributes (age, residency, etc.) without revealing the actual data.
  - Reason: Privacy, selective disclosure.
• Proof of humanity
  - Example: The World ID protocol uses ZKPs and biometric iris scans to verify users as unique individuals without revealing personal information; users can privately prove their verified human status for various actions, with only their uniqueness disclosed.
  - Reason: Privacy, selective disclosure.
• Voting
  - Example: ZKPs are employed in blockchain voting systems (e.g., MACI Minimal Anti-Collusion Infrastructure) to prove votes are valid without exposing voter identity.
  - Reason: Privacy, auditability.

Wrapping Up

To sum it up: zk-rollups are the secret ingredient making blockchains ready for prime time. They pack transactions tight, slice fees, and keep things running smoothly. But if you want privacy, read the fine print, as zk doesn’t mean invisible. The tech is moving fast, so keep watching this space, and we will keep you updated too!