Blockchain sets itself apart from centralised entities through its transparent and trustless nature. While this transparency builds trust, it also comes with a major drawback: privacy, as every transaction detail, like transaction amount, is visible to the public.
Zero-Knowledge (ZK) proofs come in to assuage privacy concerns, letting users prove that something is true without revealing sensitive details. In greater detail, let’s break down what ZK proofs are, why they matter in blockchain, and how they help shore up digital privacy.
What Is a Zero-Knowledge (ZK) Proof?
ZK proofs, also known as ZKPs, let someone prove a claim is true (e.g., ‘I have enough funds’) without revealing the underlying data (e.g., exact account balance). This is the essence of a ZK proof. It involves:
The prover
The verifier
A secret (a password or piece of data that the verifier wants to keep private)
The prover convinces the verifier they know the secret, without actually exposing it. In technical terms, ZK proofs are cryptographic methods that allow proof of knowledge without disclosure of knowledge.
A ZK proof of a statement must satisfy three key properties:
Completeness: If the statement is true, an honest verifier (one who follows the protocol correctly) will be convinced by an honest prover.
Soundness: If the statement is false, no dishonest prover can convince an honest verifier that it is true, except with a very small probability.
Zero-Knowledge: If the statement is true, the verifier learns nothing beyond the fact that the statement is true. Essentially, knowing the statement (without the secret) is enough for the verifier to envision a scenario that demonstrates the prover’s knowledge of the secret.
Why Blockchains Need ZK Proofs
ZK proofs are becoming a foundational tool for privacy, scalability, and compliance in decentralised systems. Below is why they matter:
1. Privacy Without Exposure
ZK proofs let users prove facts — like their identity, age, or the validity of a transaction — without revealing any personal information. This is critical for privacy-focused cryptocurrencies or privacy layers on Ethereum.
2. Trust Without Centralisation
In decentralised finance (DeFi), ZK proofs can verify complex interactions (like loan eligibility or asset holdings) without relying on a central authority. This maintains censorship-resistance while enabling privacy.
3. Smarter Scaling
Since ZK proofs allow for compact proofs, they reduce the data volume that needs to be stored or transmitted on-chain. This contributes to more scalable Layer-2 solutions (like ZK rollups), where thousands of transactions can be verified with a single proof.
Real-World Use Cases:
Confidential DeFi protocols
Privacy-preserving voting systems
Identity proof without data exposure (great for Web3 logins and KYC)
A Note on Current Limitations:
Resource intensive: Generating and verifying ZK proofs can be computationally demanding.
Still evolving: Standards and tooling are improving, but it’s still the early stages for many use cases.
Types of ZK Proofs Explained
There are several types of ZK proofs. Below are the main types broken down broadly:
Interactive ZK Proofs
This works like a back-and-forth Q&A. The verifier asks the prover multiple questions to gain confidence that the prover really knows the secret.
Properties:
Require back-and-forth interaction, making them less efficient for some applications.
Typically rely on computational assumptions.
Pros: Simple to design for specific problems.
Cons: Require multiple rounds; less efficient for large-scale systems.
Non-Interactive ZK Proofs
No need for back-and-forth, as the prover generates a single, self-contained proof that the verifier can check using predetermined parameters without further interaction.
Properties:
More efficient for applications requiring a single proof transmission.
Often rely on stronger cryptographic assumptions.
Often require a trusted setup phase or rely on common reference strings (CRS).
Pros: Efficient for applications like blockchain; no need for real-time interaction.
Cons: Setup phase (e.g., CRS) can be complex or require trusted parties.
Examples:
Zero-Knowledge Succinct Non-Interactive Argument of Knowledge (ZK-SNARK): A type of ZK proof that is succinct (short proofs, fast verification) and widely used. It relies on a trusted setup for the CRS. Zcash utilises ZK-SNARKs for private transactions, proving transaction validity without revealing details.
Zero-Knowledge Scalable Transparent Argument of Knowledge (ZK-STARK): Functionally similar to ZK-SNARKs, but designed to be scalable and ‘transparent’. A trusted setup phase is not required. Starknet is an Ethereum ZK rollup solution that adopted ZK-STARK.
Bulletproofs: Enable proving that a committed value is in a range using a logarithmic number of field and group elements (in the bit length of the range). Monero uses bulletproofs to obfuscate transaction amounts.
Quick Comparison: ZK-SNARK vs ZK-STARK
Feature
ZK-SNARK
ZK-STARK
Trusted Setup
Required (relies on common reference string; can be risky if compromised).
Not required (uses transparent, publicly verifiable randomness).
Transparency
Less transparent due to trusted setup.
Fully transparent (no need to trust setup participants).
Scalability
Prover/verifier time scales linearly with computation complexity.
Scales quasilinearly, making it more efficient for large computations.
Proof Size
Smaller (hundreds of bytes).
Larger (tens to hundreds of kilobytes).
Verification Speed
Fast for small proofs.
Generally slower due to larger proof size, but improves with larger datasets.
Examples
Zcash, Tornado Cash, Aztec
Starknet, dYdX, Immutable X
Conclusion: Where ZK Proofs Are Taking Web3 Privacy
As blockchain matures, so do its demands for smarter privacy, better user control, and seamless security. ZK proofs are not just nice to have; they are becoming essential. In the coming years, ZK proofs will likely:
Power identity verification without KYC data leaks.
Drive scalable Layer-2 solutions in networks like Ethereum.
Enable compliance with privacy (e.g., provable AML checks, without exposing data).
Become embedded in wallets, DeFi, and decentralised autonomous organisations (DAOs) for private governance and voting.
For developers, ZK proofs open new design patterns. For users, they promise a safer, more respectful web. Understanding them now gives users an edge in the privacy-first future that Web3 is rapidly heading towards.
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