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Architecture overview

What is the demo dapp?​

The ZKP demo dapp is a production-ready privacy-preserving token system built on Chromia that demonstrates how to implement confidential transactions using zero-knowledge proofs. It creates a complete dual-token ecosystem where users can seamlessly move between public and private token representations while maintaining full transaction privacy.

Core concept​

The dapp implements a UTXO-based privacy model, where:

  • Public tokens (FT4) exist transparently on the blockchain
  • Private tokens exist as cryptographic commitments with hidden amounts
  • Shield operations convert public tokens to private commitments
  • Private transfers move private tokens between users with complete anonymity
  • Unshield operations convert private tokens back to public tokens

This creates a confidential transaction layer on top of Chromia's blockchain, giving users the choice between public and private transactions.

Technical architecture​

Multi-layer architecture​

The dapp consists of three tightly integrated layers:

1. Circom zero-knowledge circuits​

Technology stack: Circom, PLONK proof system, Groth16 (backup)

Key features:

  • PLONK proofs for efficient verification
  • Poseidon hashing for circuit-friendly cryptography
  • Nullifier generation to prevent double-spending
  • Commitment schemes for amount hiding

2. Rell dapp (blockchain layer)​

Technology stack: Rell, Chromia Postchain, FT4 Framework, ZKPGTXModule

Security features​

  • ZKP verification using ZKPGTXModule for all private operations
  • Double-spending prevention through nullifier tracking
  • Input validation ensuring only valid commitments can be spent
  • State consistency maintaining accurate UTXO sets

3. Next.js client (frontend layer)​

Technology stack: Next.js, React, TypeScript, MetaMask integration, Chromia FT4Client

Key features:

  • SecureNoteManager for client-side key management and note encryption
  • FT4Client integration for seamless blockchain interaction
  • MetaMask wallet connection for user authentication and signing
  • ZKP proof generation in the browser using WebAssembly circuits
  • Private key derivation from wallet signatures for note decryption
  • Intuitive UI for shield, unshield, and private transfer operations