What Are Zero-Knowledge Proofs and ZK-Rollups?

Zero-Knowledge Proofs Overview

Zero-knowledge proofs are a cryptographic breakthrough that allows someone to prove a statement is true without revealing any information beyond its validity. Imagine proving you're old enough to vote without showing your birth date, or demonstrating you have enough money for a purchase without revealing your bank balance. This seemingly magical property has applications far beyond simple privacy — it's becoming the foundation for scaling the world's blockchains.

In the blockchain world, zero-knowledge technology has evolved from an academic curiosity into a cornerstone of Ethereum's scaling roadmap. What began as a theoretical solution to blockchain's capacity limitations has matured into production-ready infrastructure processing millions of daily transactions. By November 2025, ZK-rollups — Layer 2 networks powered by zero-knowledge proofs — have become essential to Ethereum's vision of scaling to billions of users without sacrificing decentralization or security.

What Are Zero-Knowledge Proofs?

Let's start with an analogy that makes zero-knowledge proofs easy to understand.

The Cave Analogy

Imagine a cave with two entrances that connect in the middle through a locked door. You know the secret password to open the door. Your friend wants proof that you know the password, but you don't want to tell them what it is.

Here's what happens:

1. You enter the cave while your friend waits outside

2. You randomly choose to go through either the left or right entrance

3. Your friend then shouts which entrance they want you to exit from

4. Because you know the password, you can unlock the door if needed and exit from the correct side

5. After repeating this process many times, your friend becomes convinced you know the password — without ever learning what it is

This is the essence of a zero-knowledge proof: proving you possess knowledge without revealing the knowledge itself.

How This Applies to Blockchain

In blockchain applications, zero-knowledge proofs work similarly. A "prover" (like a rollup network) can prove to a "verifier" (like Ethereum) that thousands of transactions were executed correctly — without the verifier needing to check each transaction individually. The verifier only needs to check a small cryptographic proof, saving massive amounts of time and computational resources.

Two Faces of Zero-Knowledge: Scaling vs. Privacy

There are two distinct applications of ZK technology:

1. ZK for Scaling (Transparent Ledgers)

Projects like zkSync Era, Scroll, Linea, and Starknet use ZK proofs to compress thousands of transactions into one validity proof, saving space and gas costs. These networks use zero-knowledge technology purely for efficiency: bundling many transactions together and proving they're all valid with a single compact proof. 

However, the ledger remains fully public — every transaction is visible on block explorers, just like on Ethereum. This makes them ideal for decentralized finance, NFT marketplaces, and any application requiring public verifiability while benefiting from lower costs and faster processing.

Using a ZK-rollup like zkSync or Scroll does NOT make your transactions private. They're as transparent as Ethereum — just faster and cheaper.

2. ZK for Privacy (Encrypted Transactions)

Privacy coins like Monero (XMR) and Zcash (ZEC) use zero-knowledge proofs in a fundamentally different way — to hide transaction details while still proving their validity. Monero uses ring signatures combined with stealth addresses to obscure transaction origins and destinations, while Zcash employs zk-SNARKs to enable completely shielded transactions where amounts, senders, and recipients can all be hidden. In the case of Zcash, users have the flexibility to choose between transparent and shielded transaction options. 

These technologies enable true financial privacy where transactions can be verified as legitimate without revealing sensitive information about who is transacting or for how much.

What Are ZK-Rollups?

ZK-rollups are a Layer 2 scaling solution that bundles hundreds or thousands of transactions together, processes them off-chain, and then submits a single cryptographic proof to the Ethereum mainnet. This dramatically reduces the amount of data that needs to be processed on the main chain.

How ZK-Rollups Work

1. Transaction Batching: Multiple transactions are collected and grouped together off-chain.

2. Off-Chain Execution: These transactions are executed on the Layer 2 network.

3. Proof Generation: A zero-knowledge proof is created that cryptographically verifies all transactions in the batch are valid.

4. On-Chain Verification: Only the proof and minimal transaction data are submitted to Ethereum.

5. State Update: Ethereum verifies the proof and updates its state accordingly.

The entire process takes minutes rather than days, and it's far more efficient than processing each transaction individually on Layer 1.

Types of Zero-Knowledge Proofs

There are two different types of zero-knowledge proofs:

zk-SNARKs (Zero-Knowledge Succinct Non-Interactive Arguments of Knowledge)

zk-SNARKs produce very small proofs that are fast to verify, making them ideal for blockchain applications where minimizing on-chain data is crucial. However, they require a "trusted setup" ceremony where initial parameters are generated, and if these parameters are compromised, the security of the entire system could be at risk. Despite this trade-off, zk-SNARKs remain popular due to their efficiency. They're used by zkSync, Polygon zkEVM, and Linea.

zk-STARKs (Zero-Knowledge Scalable Transparent Arguments of Knowledge)

zk-STARKs eliminate the need for a trusted setup, making them more transparent and theoretically more secure. They're also quantum-resistant, meaning they should remain secure even as quantum computers become more powerful. The trade-off is that zk-STARK proofs are larger than zk-SNARK proofs, making them slightly more expensive to verify on-chain. Starknet is the primary project using zk-STARKs.

The EIP-4844 Revolution

Ethereum's EIP-4844 (Proto-Danksharding), implemented in early 2024, transformed the rollup landscape by introducing "blob" transactions. This innovation slashed data availability costs — historically the biggest expense for rollups — by 30-50% or more.

What Changed

Before EIP-4844, rollups paid expensive calldata costs to post transaction data on Ethereum's permanent storage. After the upgrade, rollups use cheaper "blob space" — temporary data storage that's automatically pruned after approximately 18 days but remains available long enough for security purposes. This cost reduction made ZK-rollups economically competitive with optimistic rollups and accelerated adoption throughout 2024-2025.

ZK-Rollups vs. Optimistic Rollups

Both are Layer 2 scaling solutions, but they use different approaches to verify transactions:

While Optimistic rollups still lead in Total Value Secured, ZK-rollups have closed the compatibility gap entirely. Projects like zkSync Era, Polygon zkEVM, Scroll, and Linea have been on mainnet for extended periods by 2025, allowing developers to deploy Solidity code directly without learning new programming languages. The main practical difference users experience is withdrawal time — ZK-rollups enable much faster bridging back to Ethereum.

Top ZK-Rollup Projects in 2025

Here are some of the top zk-rollup projects to watch:

Linea

Developed by ConsenSys — the team behind MetaMask — Linea has seen massive adoption due to seamless wallet integration that enables one-click onboarding through the world's most popular Ethereum wallet. The network is available directly through MetaMask, removing friction for users already familiar with the wallet interface. 

Linea represents the "institutional-grade" ZK-EVM with its focus on security audits, regulatory compliance considerations, and integration with established DeFi protocols. The network is fully EVM-equivalent, allowing developers to use the same code as Ethereum on Linea.

Mantle Network (MNT)

Mantle completed a significant upgrade in 2025 to become the first OP Stack L2 to launch as a ZK Validity Rollup, combining the efficiency of optimistic rollups with the cryptographic security of ZK proofs. With over $2 billion in total value secured according to DeFiLlama, Mantle is now one of the largest ZK rollups. 

The hybrid architecture separates validators and relayers into distinct components, reducing systemic risk — if one part is compromised, the rest of the system remains secure. ZK proofs add cryptographic finality while the Threshold Signature Scheme (TSS) staking distributes control across a broader set of participants.

Starknet (STRK)

Starknet remains a throughput leader, powered by its custom Cairo programming language and STARK proofs that are quantum-resistant and require no trusted setup. In mid-2025, StarkNet reached Stage 1 decentralization — a milestone in Vitalik Buterin's framework for rollup networks that indicates the network has passed key technical and governance thresholds bringing it closer to full decentralization. 

The average transaction fee on StarkNet is around $0.02, with the network recording over 127 TPS in late 2024 and sub-2-second confirmation times. The STRK token is used for governance and staking within the ecosystem.

Scroll (SCR)

Scroll offers "bytecode compatibility" with the Ethereum Virtual Machine — meaning it's virtually identical to Ethereum for developers. Any code that runs on Ethereum runs on Scroll without requiring any modifications. 

ZKsync Era (ZK)

ZKsync has evolved into the "Elastic Chain" — a network of interoperable Hyperchains that share liquidity and security while allowing each chain to customize its parameters. The network has processed around 465 million transactions since launch with an average block time of 2 to 4 seconds, and average fees of around $0.03 per transaction. 

ZKsync offers native account abstraction at the protocol level, making crypto wallets significantly easier for mainstream users by enabling features like social recovery, session keys, and gasless transactions.

Polygon (POL) & The AggLayer

Polygon has evolved beyond its sidechain origins, rebranding its token to POL and launching the Aggregation Layer (AggLayer) — technology that unifies liquidity across multiple ZK chains, making them feel like a single chain from the user's perspective. 

Polygon zkEVM is fully EVM-equivalent and maintains opcode compatibility with the Ethereum Virtual Machine, enabling developers to bring their smart contracts to the network with minimal support required. 

ZK Beyond Ethereum

While Ethereum was the testing ground, ZK technology has now expanded across the entire crypto ecosystem.

Bitcoin's ZK Layer: Citrea & BitVM

For over a decade, Bitcoin was considered too simple for smart contracts due to its deliberately limited scripting language. In 2025, projects like Citrea are changing this paradigm using BitVM — a novel construction that enables complex computations to be verified on Bitcoin without changing its core protocol. 

Citrea operates as a ZK-rollup for Bitcoin that verifies proofs natively on the Bitcoin network, allowing users to deploy their BTC in DeFi applications with Bitcoin's unparalleled security guarantees. This breakthrough unlocks dormant capital that was previously locked in Bitcoin's non-programmable environment, bringing programmability to the largest and most secure blockchain without compromising its conservative design philosophy.

Solana's ZK Compression

Solana uses ZK technology in a completely different way from Ethereum — not for transaction rollups, but for state compression. Through innovations like Light Protocol and Helius, Solana developers now use ZK Compression to dramatically reduce on-chain storage costs. Instead of storing expensive data like token balances directly on-chain where storage is costly, developers store only a tiny ZK "fingerprint" on-chain while keeping the actual data in cheaper off-chain storage. 

This approach has reduced the cost of operations like airdropping tokens to millions of users by nearly 1,000x, making Solana the most cost-effective chain for massive-scale consumer applications in 2025.

Privacy Coins: Monero and Zcash

The privacy coin landscape showcases two different approaches to using zero-knowledge technology for transaction privacy. 

Monero (XMR) uses ring signatures, stealth addresses, and RingCT (Ring Confidential Transactions) to provide mandatory privacy for all transactions — amounts, senders, and receivers are automatically obscured. Every transaction mixes with others to hide its origin, making Monero the most private cryptocurrency by default. 

Zcash (ZEC), on the other hand, employs zk-SNARKs to enable shielded transactions but gives users a choice — transactions can be fully transparent, fully shielded, or a mix of both. Shielded transactions completely hide all transaction metadata while still being cryptographically verifiable as valid.

Programmable Privacy L1s

New Layer 1 blockchains are embedding ZK technology directly into their architecture to enable private applications, not just private payments.

Aleo takes a radical approach where users execute transactions locally on their own device, generating ZK proofs of correct execution, and only send these proofs to the network. This keeps user data and application logic entirely off-chain while still enabling public verification that rules were followed. The result is a platform where users can run private applications — from private DeFi strategies to confidential voting systems — without revealing sensitive information to the network.

Midnight, a partner chain for Cardano, focuses on selective disclosure and regulatory compliance. The platform allows businesses and individuals to prove specific statements about themselves — such as "I am over 18 years old" or "I have sufficient funds for this transaction" — without revealing underlying personal information like exact age or bank balance. This selective disclosure model makes Midnight particularly attractive for enterprise applications that must balance privacy requirements with regulatory compliance.

Challenges Facing Zero-Knowledge Projects

Despite significant progress, ZK technology still faces several obstacles that projects are actively working to overcome.

Prover Centralization

While ZK-rollup networks themselves are decentralized with distributed validators and open participation, the specialized servers that generate zero-knowledge proofs (called "provers") are often run by the founding teams or a small set of entities. Generating ZK proofs requires significant computational resources — often necessitating powerful GPUs or custom ASICs — which creates barriers to entry for independent operators. If a single entity controls proof generation, it could theoretically censor transactions by refusing to include them in proofs. 

Projects are addressing this through hardware acceleration to lower costs, decentralized prover networks with economic incentives, and ongoing research into more efficient proof systems that reduce computational requirements.

Liquidity Fragmentation

The ZK ecosystem now includes multiple competing chains — Scroll, zkSync, Linea, Polygon zkEVM, Starknet, and more — each with its own isolated liquidity pool. A user with assets on zkSync cannot easily interact with applications on Scroll without bridging funds, creating friction and splitting capital across ecosystems. 

This fragmentation means DeFi protocols must choose which chains to deploy on, developers must build cross-chain infrastructure, and users face a confusing landscape of disconnected networks. Solutions emerging include Polygon's AggLayer technology that creates a unified liquidity layer across ZK chains, zkSync's Elastic Chain architecture for seamless interoperability between Hyperchains, and cross-chain messaging protocols that enable atomic swaps and unified state across rollups.

Proving Time and Costs

Generating zero-knowledge proofs remains computationally intensive and can take minutes to hours depending on the complexity of the computation being proven. This creates latency in transaction finality and increases operational costs for rollup operators. While proof verification on Ethereum is quick, the generation process requires substantial resources. 

The industry is addressing this challenge through better software that generates proofs faster, specialized computer chips designed for ZK calculations, and techniques that combine multiple proofs into one to improve efficiency. As these technologies mature, proof generation is becoming faster and cheaper.

Developer Education and Tooling

Understanding zero-knowledge cryptography requires specialized knowledge, creating a steep learning curve. Additionally, debugging ZK circuits when things go wrong is significantly more challenging than traditional smart contract development. The ecosystem is addressing this through improved developer documentation and tutorials, abstraction layers that hide cryptographic complexity, better error messages and debugging tools, and educational programs and workshops focused on ZK development.

The Future of ZK Technology

As we look toward 2026 and beyond, several trends are shaping the evolution of zero-knowledge technology.

Ethereum's Fusaka Upgrade

Ethereum's Fusaka upgrade is scheduled to activate on the mainnet on December 3, 2025. This major network upgrade includes improvements specifically designed to make zero-knowledge rollups more efficient and cost-effective.

The upgrade's most significant feature for ZK technology is the introduction of new opcodes and optimizations that will dramatically reduce the computational cost of generating zero-knowledge proofs. By making certain cryptographic operations more efficient at the protocol level, Fusaka is expected to lower ZK proving costs substantially, making ZK-rollups even more economical to operate.

Additionally, Fusaka introduces PeerDAS (Peer Data Availability Sampling), which allows the network to handle more rollup data without requiring every node to store everything. This enables Ethereum to support significantly more ZK-rollup activity, furthering the network's capacity to scale through Layer 2 solutions.

Vitalik's Long-Term Vision

Ethereum co-founder Vitalik Buterin has consistently stated that zero-knowledge rollups will become the dominant scaling solution in the mid to long term as the technology matures. His ongoing research and proposals focus on making ZK proofs faster and cheaper to generate, which would further accelerate ZK-rollup adoption and make them more accessible to a wider range of applications.

Amazing to see so many major L2s now at stage 1.

The next goal we should shoot for is, in my view, fast (<1h) withdrawal times, enabled by validity (aka ZK) proof systems.

I consider this even more important than stage 2.

Fast withdrawal times are important because waiting a… https://t.co/YZs2hQ3Wrn

— vitalik.eth (@VitalikButerin) August 6, 2025

Growing Institutional Interest

The zero-knowledge ecosystem is attracting attention from traditional financial institutions exploring blockchain technology for private, compliant transactions. Projects like Deutsche Bank's blockchain initiatives have explored ZK technology for identity verification and tokenized asset transactions, demonstrating institutional interest in privacy-preserving blockchain solutions. According to Communications of the ACM, ZK proofs enable institutions such as banks to interact with public blockchain networks while maintaining data privacy and regulatory compliance — addressing a critical barrier to institutional adoption.

Regulatory frameworks are also evolving to accommodate privacy-preserving technologies. The U.S. GENIUS Act and CLARITY Act have provided clearer rules for digital assets and market structure, reducing uncertainty for institutions considering blockchain adoption. Meanwhile, ZK-rollup networks continue to demonstrate their capacity to handle significant transaction volume, with major networks processing over a million daily transactions.

Conclusion

In 2023, the question was "Will ZK-rollups work?" In 2025, the question is "Which ZK ecosystem will you build on?"

With technical barriers of cost and compatibility removed through EIP-4844 and mature ZK-EVMs, zero-knowledge proofs have evolved from a niche Ethereum scaling solution into the foundational privacy and scaling layer for the entire Web3 ecosystem. The technology has proven itself in production across multiple chains, processing billions of transactions and securing billions of dollars in value.

Whether you're a developer seeking scalability, an institution requiring privacy, or a user wanting instant finality and low fees, ZK technology now offers production-ready solutions across multiple blockchains. The upcoming Fusaka upgrade will further cement zero-knowledge proofs as essential infrastructure for the future of blockchain technology.

Glossary: Key Terms Explained

EVM-Compatible: A blockchain that can execute Ethereum code with minor modifications (example: zkSync Era).

EVM-Equivalent: A blockchain that perfectly mimics Ethereum's execution environment with no modifications required (example: Scroll, Polygon zkEVM).

Type-1 zkEVM: Fully equivalent to Ethereum with no changes to EVM specifications, prioritizing compatibility.

Type-2 zkEVM: Equivalent to EVM but with minor modifications for better proof generation efficiency.

Validity Proof: A cryptographic proof that a batch of transactions was executed correctly according to the rules.

Data Availability: Ensuring that transaction data is accessible for verification by anyone who needs it.

Sequencer: The entity that orders and batches transactions in a rollup before they're proven.

Prover: The entity that generates zero-knowledge proofs demonstrating transaction validity.

Blob: A temporary data package introduced with EIP-4844 that rollups use to post transaction data cheaply.

Finality: The point at which a transaction is considered irreversible and permanently part of the blockchain.

This article is only for informational purposes and should not be taken as investment advice. Always do your own research before depositing your assets in any crypto technology.

The original version of this article was contributed by CJ.