What is zKVM? - A Complete Guide to Zero-Knowledge Virtual Machines

The blockchain realm is constantly evolving, and one of the most exciting innovations in recent years is Zero-Knowledge Virtual Machine (zKVM). At its core, this zKVM is a system that permits complicated computations to be verified, without revealing the underlying data. This indicates that information can remain private while still proving that the results are accurate. 

Here in this blog, we are going to explore what zKVM actually is and its ecosystem, key factors and much more., Before delving into the topic, let's see a glimpse of ZKP (Zero-Knowledge Proofs).

What is Zero Knowledge Proof (ZKPs)?

A Zero Knowledge Proof (ZKPs) is a cryptographic protocol that allows a prover to convince a verifier that the certain statement is true, without revealing any excess information beyond the validation of the statement. 

In Simple Terms: 

- You need to prove you know something (like the numbers or the result). 

- But you don't reveal what you know. The zero-knowledge part means I learn absolutely nothing about your result.

- The proof is just a checkmark. The process turns a complex computation into a simple "Yes, this was done correctly" signal. This is why it's so useful for things like verifying a transaction without knowing the amount.

While ZKPs can be used for privacy, their use in zkVMs mainly prioritizes succinctness, not only privacy. They create a tiny proof that a large computation was done correctly. This proof is much faster to verify. This blend of security & scalability is what makes ZW cryptography so powerful for applications that need to be both trustworthy and efficient.

Types of Zero-Knowledge Proofs

There are only two mainly used types in ZKPs: zk-SNARKs and zk-STARKs. The choice between these proof systems is a critical architectural decision for a zkVM, as it dictates the design and implementation of its components.   

zk-SNARKs

zk-SNARKs (Zero-Knowledge Succinct Non-Interactive Arguments of Knowledge), which is super capable of producing smaller and efficient proofs, which can be verified faster. A key limitation is the zk-SNARKs is it requires a trusted setup (one-time process).  

zk-STARKs 

zk-STARKs (Zero-Knowledge Scalable Transparent Arguments of Knowledge) utilize a different cryptographic foundation, which renders them transparent. This leads to them not requiring a trusted setup, like zk-SNARKs. Scalability is easy to achieve with Zk-STARKs, but they typically generate larger proofs than zk-SNARKs.

What is zkVM?

The core challenge of the Web3 ecosystem is the problem of verifiable computation. Traditional systems rely on re-executing a program to verify its output, which is a slow, costly, & also resource-intensive process. This approach creates bottlenecks, particularly in decentralized environments like blockchains.

“A new model was required to move beyond this inefficient model.“

That's where the new paradigm is embodied by the Zero-Knowledge Virtual Machine (zkVM). In its simplest form, a zkVM is a virtual machine that can generate a Zero-Knowledge Proof (ZKP) to cryptographically verify one party to prove the validity of a statement to another party without revealing any additional or underlying information, unlike a traditional Virtual Machine (VM).

ZK algorithms used to create a succinct proof. This means the proof is small in size and can be verified exponentially faster than re-executing the original program, saving time and computational resources. This property of succinctness is the basis for what makes ZK layer-2 blockchains scalable and efficient.

The evolution of this technology follows a clear logical progression. The problem of resource-intensive re-execution created the need for a new solution. Zero-knowledge proofs emerged as the technological primitive to enable verification without re-execution. 

The zkVM then emerged as the critical abstraction layer, a "universal circuit" that makes ZK proofs accessible by allowing developers to write provable programs in familiar languages without needing deep cryptographic expertise. This fundamental shift in the computation is the primary driver of the benefits that zkVMs bring to the Web3 space.

Difference Between zkVM vs Traditional VM

A zkVM differs from traditional systems in various aspects. Here are some of the key differences between zkVM & traditional VMs.

In essence, a traditional system's core function is computation, with security and privacy addressed. A zkVM, by contrast, is fundamentally a verifiable computer designed for trustless environments like Web3.

How Does a zkVM Really Work?

Understanding how a zkVM functions requires a look at its multi-stage process. This process can be abstracted into four primary stages:

The Compiler Stage:

This is the initial step where a program written in an ordinary language like Rust, C++, or Solidity is converted into machine code (VM-readable code). 

The Virtual Machine (VM) Stage:

The VM executes the machine code generated by the compiler. Without revealing information about the program, and generates an execution trace. This trace is formatted to conform to a specific cryptographic standard. This format is predetermined by an arithmetic scheme, such as R1CS, PLONKish, and AIR.

The Prover Stage:

This stage where all the magic of zero-knowledge proofs happens. The prover takes the execution trace and converts it into a series of complex algebraic polynomials. 

The prover then commits to these polynomials using a Polynomial Commitment Scheme (PCS) and performs a Polynomial Interactive Oracle Proof (PIOP) to confirm that the polynomials satisfy the necessary constraints of the computation. Finally, the prover produces a small, succinct.

The Verifier Stage: 

This is the final step. The verifier receives the succinct proof from the prover and checks its validity against the established verification protocol. The verifier either accepts or rejects the proof, which gives the integrity of the computation without the need for resource-intensive re-execution. 

Behind zkVMs, the choice between SNARKs & STARKs is a fundamental design decision that shapes the entire system. Both are powerful forms of zero-knowledge proofs that enable efficient verification of complex computations.

SNARKs are known for their incredibly small proof sizes and also have fast verification times. STARKs, on the other hand, are transparent, meaning they do not require a trusted setup, making them more trustless & secure.

Why zkVMs Are a Game-Changer?

Combining the deterministic nature of a virtual machine with the cryptographic power of zero-knowledge proofs, zkVMs offer a triad of benefits that are central to their adoption: scalability, security, and efficiency.

They use verifiable computation to offload intensive programs to a server or another chain, which then gives a cryptographic guarantee of the output. This significantly reduces the work required for verifiers to confirm the output's legitimacy, leading to secure scalability in blockchain environments.

The power of this new model is rooted in three key cryptographic properties of the underlying zero-knowledge proof systems:

- Soundness: Guarantees that a proof system is truthful, meaning a verifier will reject proofs for false statements.

- Completeness: The proof system is able to prove all true statements. If a computation is done correctly, a prover can generate a proof that a verifier will accept.

- Zero-Knowledge: Measures the proof system efficiency, including proof size, verification time, & memory usage. This property allows zkVMs to achieve significant efficiency gains, as a small, quick-to-verify proof can represent a massive computation. 

These properties unlock tangible benefits, most notably in the realm of blockchain scaling. By allowing the bulk of smart contract execution to be moved off-chain, zkVMs can significantly speed up transaction processing & reduce costs.

zkVM-based zero-knowledge rollups offer fast finality and low transaction costs, which differ from optimistic rollups. While optimistic rollups need a one to two week challenge period for fraud proofs, zkVM-based rollups are finalized instantly once the validity proof is posted to the layer-1 blockchain. This makes them ideal for applications that need quick asset movement, like DeFi protocols.

zkVM Trilemma: Speed, Efficiency, and Succinctness

zkVMs face a key trilemma that requires developers to balance three competing factors: speed, efficiency, & also succinctness. Optimizing for one of these factors often ends up at the expense of another.

Speed:

This refers to how quickly the zero-knowledge proofs can be generated and verified without any struggle.

- Challenges: Cryptographic & mathematical operations are computationally intensive.

- Solutions: Use of specialized hardware like ASICs & GPUs, optimizing algorithms, also process parallelization can speed up computations as well.

Efficiency:

This relates to the amount of computational energy resources that are required to generate and verify proofs.

- Challenges: Resource-intensive nature of proof generation will be a major hurdle for scalability.

- Solutions: Algorithm optimization and techniques like data compression can be used to reduce the amount of information that needs to be processed.

Succinctness: 

The ability of a proof to be small, making it easy to transmit and store.

- Challenges: A proof must be small enough for quick transmission while still containing all the necessary information.

- Solutions: Advanced cryptographic techniques like SNARKs & STARKs are used to create smaller, more efficient proofs.

The trilemma lies in the fact that improving one factor often negatively impacts the others. For example, increasing speed might reduce efficiency or succinctness. 

Continuously exploring new approaches, such as hybrid algorithms and ML, to find a balance that will drive the future of blockchain technology.

zkVM Ecosystem: Key Projects Comparison

The zkVMs landscape is diverse, with projects making different architectural choices to address specific market needs.

General-purpose zkVMs are blockchain-agnostic and not tied to the EVM's architecture, offering great flexibility. It supports high-level languages like Rust, C++, & Go, which helps developers to build provable applications with existing languages & libraries instead of developing them for crypto-specific ones.

- RISC Zero, which is based on the RISC-V instruction set and allows developers to prove the correct execution of arbitrary Rust code.    

- Succinct's SP1, described as one of the fastest RISC-V zkVMs that can generate proofs for LLVM-based languages like Rust.   

- Polygon Miden, a privacy-first rollup that leverages client-side proving and local transaction execution.

zkVM vs. zkEVM: Key differences

The key similarity between zkVM & zkEVM lies in their shared use of ZKPs to provide privacy & scalability. zkVMs are used for the general purpose of various blockchain applications, while zkEVMs are specifically optimized for the Ethereum ecosystem.

Its goal is to bring the benefits of zero-knowledge proofs, scalability, security, & low cost to Ethereum without changing the existing developer experience.

Notable projects in this space include Polygon zkEVM & zkSync Era, which offer scalable & secure EVM-compatible layer-2 solutions.

Key Factors to Consider When Choosing a zkVM

Choosing between multiple zkVMs is a key decision. Each zkVM has its own limitations, so choosing the right one based on your needs is important. If you are looking to scale in the Ethereum ecosystem, zkEVM will be the best pick, while a general-purpose zkVM offers flexibility for architectural innovation.

Here are a few criteria to choose the right zkVM:

1. Define requirements: Determine the specific use case & requirements for your project.

2. zkVMs Evaluation: Assess the correctness, security, trust assumptions, & performance of each zkVM.

3. Limitation Consideration: Balance speed, efficiency, and mainly succinctness based on your project's needs.

4. Compare: Test the different zkVMs and choose the best one that meets your requirements.

Ongoing research focuses on optimizing zkVM performance through compiler optimizations (like LLVM) & hardware acceleration (using GPUs). The zkVM cost model is different from a traditional CPU, because each and every instruction must be proven. This requires specific "zkVM-aware" refinements to compiler optimizations to ensure they improve performance rather than degrade it.

Conclusion

zkVMs provide secure scalability, fast finality, & low transaction costs. They achieve this by providing a new verification model that doesn't require resource-intensive re-execution.

Beyond their use in zk-rollups, zkVMs are being applied in new areas like ZK Coprocessors, verifiable machine learning, and on-chain identity. This technology represents a fundamental shift from a trust-based to a mathematically verifiable computing model and is poised to be a cornerstone of the Web3 ecosystem.

Maticz, a leading blockchain development company, leverages zkVM technology to build a wide range of decentralized solutions. Our services include developing custom zk-rollups for enhanced scalability, creating secure and efficient DeFi protocols. By harnessing the power of zkVMs, Maticz provides innovative and reliable solutions that bring your application to the forefront of the Web3 landscape.