universal privacy Commons: 4/5

Zero-Knowledge Proofs (ZKPs)

Also known as:

1. Overview

Zero-Knowledge Proofs (ZKPs) is a pattern for building resilient value creation systems.

Problem: In many digital interactions, you need to prove that a statement is true without revealing the information that makes it true. For example, you might need to prove to a website that you are over 18 without revealing your actual birth date. Or, a company might need to prove to an auditor that it has followed certain business rules without revealing the confidential data involved in those rules.

Context: You are designing a system that requires one party (the Prover) to convince another party (the Verifier) of the truth of a statement, but the information underlying the statement is sensitive and cannot be revealed. You need a way to provide this proof without compromising the confidentiality of the underlying data.

2. Core Principles

Use a Zero-Knowledge Proof (ZKP), a cryptographic protocol where a Prover can prove to a Verifier that they know a value or that a statement is true, without conveying any information whatsoever apart from the fact that they know the value or that the statement is true.

A ZKP must satisfy three properties:

  1. Completeness: If the statement is true, an honest Prover can convince an honest Verifier.
  2. Soundness: If the statement is false, a cheating Prover cannot convince an honest Verifier (except with a very small probability).
  3. Zero-Knowledge: If the statement is true, the Verifier learns nothing other than the fact that the statement is true.

ZKPs are a complex and rapidly evolving area of cryptography, with different schemes like ZK-SNARKs and ZK-STARKs offering different trade-offs in proof size, prover time, and verifier time.

3. Rationale

ZKPs are a powerful tool for building trust in a decentralized and privacy-preserving way. They:

  • Decouple Verification from Disclosure: Allow you to verify facts without having to see the sensitive data behind them.
  • Enhance Privacy: Provide one of the strongest possible forms of data minimization.
  • Enable Scalability (in blockchains): Can be used to verify complex computations off-chain and then submit a small proof to a blockchain, increasing throughput.

4. Consequences

  • Positive:
    • A revolutionary tool for privacy and trust.
    • Enables a wide range of new privacy-preserving applications.
    • Can be used to improve the scalability and privacy of blockchain systems.
  • Negative:
    • Extreme Complexity: ZKPs are at the cutting edge of cryptography and are extremely complex to understand and implement correctly.
    • High Computational Cost: Generating proofs can be computationally intensive, although verification is often very fast.
    • Immaturity: The field is still evolving rapidly, and the tooling is not yet mature.

5. Application Context

Best Used For:

  • Value creation systems requiring strong privacy and security foundations
  • Organizations operating in regulated environments
  • Systems handling sensitive data or requiring high trust

6. Known Uses

  • Zcash: A privacy-focused cryptocurrency that uses ZK-SNARKs to shield the sender, receiver, and amount of a transaction.
  • Identity Management: Being explored as a way to prove identity attributes (e.g., “I am a citizen of country X”) without revealing a full identity document.
  • Blockchain Scaling: ZK-Rollups are a Layer 2 scaling solution for Ethereum that use ZKPs to bundle many transactions into a single proof.