Title: Feature: Implement Zero-Knowledge Proofs (zk-SNARKs) for Confidential Evidence Verification

[Adithyakp86]

Description

Currently, the system anchors evidence hashes (SHA-256) directly to the Polygon blockchain using the EvidenceStorage.sol contract. While this ensures immutability, it potentially exposes metadata fingerprints of highly sensitive judicial evidence on a public ledger.

To achieve true "Zero-Trust Architecture" (as outlined in Phase 2) and enhance privacy, we need to implement Zero-Knowledge Proofs (zk-SNARKs). This will allow investigators and courts to cryptographically prove that a specific piece of evidence exists and remains untampered with, without ever exposing the actual hash or metadata on the public chain.

Proposed Solution

1. Circuit Generation: Write a circom circuit that takes the original evidence hash as a private input and a public commitment (e.g., a Pedersen hash) representing the case/organization.
2. Smart Contract Update: Upgrade EvidenceStorage.sol to include a verifyProof function using a generated Solidity verifier contract.
3. Backend Integration: Update the Express.js API to generate zk-proofs off-chain using snarkjs before submitting the transaction via ethers.js.
4. Verification Flow: Update the evidence-verification.js frontend module to validate the zk-proof against the blockchain state instead of doing raw hash comparisons.

Technical Stack

• circom / snarkjs
• Solidity (Verifier Smart Contract)
• Node.js / ethers.js

Acceptance Criteria

• ZK circuit compiled and verifier smart contract deployed to Polygon Amoy.
• EvidenceStorage.sol successfully upgraded to accept and verify proofs.
• Backend generates proofs dynamically upon evidence upload.
• Verification times remain under 5 seconds on the frontend.
• Comprehensive unit tests added to Hardhat (tests/).

Labels: enhancement, blockchain, hard, security

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