What is zero-knowledge proof? A complete guide

What is zero knowledge proof and how does it ensure online privacy? Learn what it is and why it’s important.

Imagine you’re keeping a secret and someone wants to confirm that you know it, but you don’t want to reveal what the secret actually is. How is this possible? Enter zero-knowledge proofs (ZKP), a cryptographic concept that allows for exactly this.

Despite their complex-sounding name, zero-knowledge proofs offer a simple but powerful idea: proving knowledge of something without revealing the details.

Introduced in the 1980s, zero-knowledge proofs have since become a cornerstone of modern cryptography, offering a path to secure and private digital interactions in an increasingly data-centric world.

Let’s understand what zero knowledge proof is, how they work, and explore the various fields where they find applications.

Description of zero knowledge proof (ZKP)

ZKPs are a method of encryption that allows one party, known as a prover, to show another party, the verifier, that it has certain information without actually revealing that information.

In simpler terms, ZKPs allow information to be verified without revealing its actual content. One of the most famous analogies illustrating zero-knowledge proofs is the “Ali Baba Cave” scenario:

Imagine that a verifier named Peggy wants to prove to Victor, a verifier, that he knows the secret password to enter a cave without actually revealing the password.

Peggy takes Victor to the cave entrance, goes in, and then exits by a different route. He then challenges Victor to identify the original entrance he used.

If Victor can find the original login, Peggy will reveal the password. However, if Victor cannot find the original login, Peggy successfully proves her knowledge of the password without revealing it.

In this analogy, the cave represents secret knowledge (the password), and Peggy’s ability to enter and exit the cave demonstrates her knowledge of the password.

More importantly, Victor cannot obtain any information about the password itself, as he cannot see which entrance Peggy used to exit the cave.

This example reflects how zero-knowledge proofs allow a party to prove knowledge of a secret without revealing the secret itself.

ZKPs have broad applications in areas such as authentication, privacy-preserving protocols, and blockchain technology.

How do zero knowledge proofs work?

Zero-knowledge proof is achieved through a complex series of interactions. At the core of ZKPs are mathematical algorithms and protocols that make this interaction possible.

A common type of ZKP is the interactive protocol, in which the prover and verifier perform a series of steps to determine the validity of the statement.

These steps are designed so that the verifier can be convinced of the prover’s knowledge without the prover having to reveal any specific information.

For example, consider a scenario in which Donald wants to prove to Joe that he knows a secret trick.

This is accomplished through a series of cryptographic calculations and exchanges that allow Joe to verify the accuracy of Donald’s claim without learning anything about the secret number.

ZKPs have wide-ranging applications. ZKPs are used in authentication and privacy-preserving protocols as well as blockchain technology.

For example, in a blockchain network, ZKPs can be used to prove the validity of transactions without revealing sensitive information such as the sender’s address or transaction amount.

Types of zero-knowledge proofs

Zero-knowledge proofs (ZKPs) come in several types, each serving specific purposes and offering unique advantages.

The two main types include interactive and non-interactive ZKPs and several others, each with their own features and applications.

Interactive Zero Knowledge Proofs (ZKIPs): Interactive ZKPs require the prover and verifier to engage in a series of interactions to verify the proof. The verifier presents challenges or questions to the prover, which he must answer correctly based on his possession of secret knowledge. An example is the Schnorr protocol, which is used to prove the knowledge of a discrete logarithm without revealing it.
Non-Interactive Zero Knowledge Proofs (NIZKs): Introduced in 1988, non-interactive ZKPs eliminate the need for interaction by using cryptographic algorithms based on pre-decided parameters. Proofers enter their information into an algorithm to create a proof; then the verifier checks this using another algorithm. Although more efficient, NIZKs are computationally intensive. Examples include zk-SNARKs and zk-STARKs. zk-SNARK (Zero-Knowledge Concise and Non-Interactive Knowledge Argument): zk-SNARKs allow a verifier to verify a statement without knowing additional details about it. They are concise, non-interactive and eliminate the possibility of cheating by meeting the ‘robustness’ requirement. zk-SNARKs are used in projects such as zkSync and Polygon zkEVM.
zk-STARK (Zero-Knowledge Scalable Transparent Information Argument): zk-STARKs are similar to zk-SNARKs but offer scalability and transparency. They are faster for larger witness sizes and generally rely on verifiable randomness rather than a reliable setup. StarkNet uses zk-STARKs for scalability and transparency in its operations. Statistical Zero-Knowledge Proofs: Statistical ZKPs allow a prover to convince a verifier with high probability rather than certainty. They are useful in situations where absolute precision is not required, as is the case with certain cryptographic protocols.
Knowledge Arguments: Knowledge arguments ZKPs prove that the prover knows a secret without revealing it. The Sigma protocol is an example used in digital signatures.
Non-Black Box Zero Knowledge Proofs: These proofs allow the verifier to examine the inner workings of the proof for additional information and provide transparency in certain cryptographic applications.
Zero-Knowledge Proofs: These proofs not only prove knowledge of a secret, but also knowledge of how to obtain it. The Schnorr identification protocol used in digital signatures is an example. Zero knowledge proof applications

Zero-knowledge proofs have a wide range of applications across various industries and technologies thanks to their ability to increase privacy, security, and efficiency in digital interactions.

Blockchain technology: One of the most prominent applications of ZKPs is blockchain technology. ZKPs can be used to prove the validity of transactions without revealing sensitive information such as the sender’s address or transaction amount. This can help improve privacy and scalability in blockchain networks. For example, ZKPs are used in Zcash (ZEC), a privacy-focused cryptocurrency. ZKPs allow users to prove ownership of funds without revealing their transaction history or account balance.
Authentication: Zero-knowledge proofs can be used for secure and privacy-preserving authentication. For example, they can be used to prove that an individual is over a certain age without revealing their exact age or date of birth. Organizations such as QEDIT leverage ZKPs to enable companies to verify the integrity of their data without disclosing it to third parties, thus ensuring data privacy.
Digital voting: ZKPs can be implemented in digital voting systems to ensure the integrity of the voting process while protecting voter privacy. ZKPs can be used to prove that a vote was cast correctly without the actual vote being revealed. An example of this is the “CIVITAS” project, which uses ZKPs to enable verifiable and anonymous voting in elections.
Data sharing and collaboration: ZKPs can enable secure and private data sharing and collaboration. For example, ZKPs can be used to prove that certain conditions are met without revealing underlying data, allowing parties to collaborate without compromising sensitive information.
Authentication and Access Control: ZKPs can enhance authentication and access control mechanisms. ZKPs can be used to prove ownership of a digital asset without revealing the asset itself, increasing security in digital transactions. For example, ZKPs are used in the “Sovrin” network to enable individuals to prove attributes about themselves, such as age or qualifications, without revealing unnecessary personal information.
Privacy-Preserving Technologies: ZKPs are also used in privacy-preserving technologies such as anonymous credentials and private set intersection protocols. These technologies enable secure interactions without revealing sensitive information. Advantages and challenges of zero-knowledge proofs

Zero-knowledge proofs (ZKPs) offer several advantages.

Advantages Privacy: One of the key advantages of ZKPs is the ability to provide confidentiality by allowing a party to prove knowledge of something without revealing the actual information. This is very important in applications where data privacy is very important, such as authentication.
Security: ZKPs increase security by enabling verifiable calculations without revealing sensitive data. This is especially important in blockchain and cryptocurrency applications where transactions must be verified without revealing transaction details.
Efficiency: ZKPs can significantly reduce the computational and communication overhead associated with proving the validity of a statement. This efficiency makes them suitable for use in resource-constrained environments.
Transparency: In some cases, such as non-interactive ZKPs that use publicly verifiable randomness, ZKPs can increase trust in the system by offering transparency in the generation and verification of evidence.
Scalability: Certain types of ZKPs, such as Zk-STARKs, offer scalability advantages, allowing efficient proof generation and validation even with large amounts of data. challenges

ZKPs also come with some challenges that need to be addressed for widespread adoption:

Complexity: ZKPs can be complex to implement and understand; Requires expertise in cryptography and mathematics. This complexity may hinder its widespread adoption and implementation.
Computational intensity: Creating and verifying ZKPs can be computationally intensive. This can lead to scalability issues, especially in high-throughput applications.
Reliable installation: Some ZKPs require a reliable installation phase to establish global parameters. Ensuring the integrity of this installation and preventing possible attacks can be difficult.
Proofer knowledge: ZKPs are based on the assumption that the secret knowledge they claim to know belongs to the prover. Validating this assumption without revealing the secret can be challenging in some scenarios.
Interoperability: Interoperability of different ZKP systems may be limited, making it difficult to use ZKPs seamlessly across different platforms and applications. road ahead

As of today, zero-knowledge proofs have emerged as a crucial technology to increase privacy and scalability in various digital applications.

Recently released ZK-powered blockchains such as Polygon zkEVM, zkSync Era, and StarkNet show great promise. Its potential applications and effects are just beginning to be explored.

It will be fascinating to see how these technologies evolve and what new possibilities they will unlock in the coming years.