Stellar Protocol 25 (X-Ray) introduced BN254 elliptic curve and Poseidon hash function support, enabling zero-knowledge proofs as a first-class feature on Soroban. The article demonstrates a practical Sudoku game example using Noir circuits and Ultrahonk verification on Stellar smart contracts.
Stellar's Protocol 25 upgrade, codenamed X-Ray, brought transformational capabilities for zero-knowledge applications by adding BN254 elliptic curve support and preliminary Poseidon hash functions to Soroban. The article provides a comprehensive introduction to ZK concepts—explaining elliptic curve cryptography, circuits, constraints, and proving systems like Groth16, PLONK, and Ultrahonk. It then walks through a real-world implementation: a Sudoku game where players prove they solved a puzzle without revealing the solution. The example uses Noir (a Rust-like DSL) to write the circuit, Barretenberg backend for proof generation, and a Soroban smart contract that verifies proofs via a single cross-contract call. The dApp allows users to deposit XLM into a prize pool and claim rewards for correct solutions, demonstrating how ZK integrates with Stellar's payment and smart contract infrastructure.
