Zero-Knowledge Sudoku

Abstract

Imagine sharing that you know a secret without revealing the secret itself. This is what zero-knowledge proofs (ZKPs) aim to do. In ZKPs there is a prover who claims knowledge of something and a verifier who checks this claim. The goal of this project is to further explore current technologies revolving around ZKPs and understand possible adaptations to an everyday application beyond blockchain use cases. To explore the practical use of ZKPs, this project introduces a web puzzle application that keeps the solutions of individual users private using ZKPs. A user can solve a logic- based puzzle like Binairo or Sudoku and check the validity of their solution by sharing only a ZKP of the solution. That way, the solution never leaves the user’s device. To further strengthen the security, the following two checks are implemented: (1) making sure that the solution matches the original puzzle, and (2) integrating the user’s ID during the generation process. These checks prevent users from reusing a proof to “solve” other puzzles or for the proof to be stolen by another user. To implement this application, different ZKP frameworks are considered. Circom and snarkjs are selected because of their active development, clear documentation and good web development capabilities. The final result is a secure application that demonstrates how ZKPs can be applied in a realistic and practical way. This highlights their broader potential in digital security. In most applications, the impact of ZKPs is intentionally hidden, as good cybersecurity aims to operate in the background. The ZKP-Puzzles application puts the ZKPs in the spotlight and visualizes how ZKPs work.