# Architecture overview · Build with zero-knowledge proofs on Chromia · Learn Chromia > This ZKP demo is a Chromia application that shows you how to build confidential transactions with zero-knowledge proofs. The source describes it as a… Source: https://chromia.com/learn/zero-knowledge-proof/architecture-overview/ Build with zero-knowledge proofs on ChromiaLesson 4 of 19 1. [01Introduction to the course](https://chromia.com/learn/zero-knowledge-proof/introduction/) 2. [02Zero-knowledge proof](https://chromia.com/learn/zero-knowledge-proof/zero-knowledge-proof/) 3. [03Project setup](https://chromia.com/learn/zero-knowledge-proof/setup/) 4. [04Architecture overview](https://chromia.com/learn/zero-knowledge-proof/architecture-overview/) Module 1: Writing Circom circuits 1. [05Overview](https://chromia.com/learn/zero-knowledge-proof/circom-circuits/) 2. [06Circom circuits: introduction](https://chromia.com/learn/zero-knowledge-proof/circom-circuits/circom-circuits-introduction/) 3. [07Circom files overview](https://chromia.com/learn/zero-knowledge-proof/circom-circuits/circom-circuits-project/) 4. [08Circom circuits: compile](https://chromia.com/learn/zero-knowledge-proof/circom-circuits/circom-circuits-compile/) Module 2 – Dapp 1. [09Overview](https://chromia.com/learn/zero-knowledge-proof/dapp/) 2. [10Dapp: setup and run](https://chromia.com/learn/zero-knowledge-proof/dapp/dapp-setup-run/) 3. [11Dapp overview](https://chromia.com/learn/zero-knowledge-proof/dapp/dapp-overview/) 4. [12Dapp entities](https://chromia.com/learn/zero-knowledge-proof/dapp/dapp-entities/) 5. [13PLONK verification](https://chromia.com/learn/zero-knowledge-proof/dapp/dapp-verification/) 6. [14Dapp operations overview](https://chromia.com/learn/zero-knowledge-proof/dapp/dapp-operations/) 7. [15Dapp queries overview](https://chromia.com/learn/zero-knowledge-proof/dapp/dapp-queries/) Module 3 – Frontend 1. [16Overview](https://chromia.com/learn/zero-knowledge-proof/frontend/) 2. [17Frontend: setup and run](https://chromia.com/learn/zero-knowledge-proof/frontend/frontend-setup-run/) 3. [18Frontend architecture](https://chromia.com/learn/zero-knowledge-proof/frontend/frontend-explore/) 4. [19Frontend: test](https://chromia.com/learn/zero-knowledge-proof/frontend/frontend-test/) [Learn](https://chromia.com/learn/)[Build with zero-knowledge proofs on Chromia](https://chromia.com/learn/zero-knowledge-proof/) 04 / 19Advanced # Architecture overview ## What is the demo dapp? This ZKP demo is a Chromia application that shows you how to build confidential transactions with zero-knowledge proofs. It demonstrates a **privacy-preserving token system**. It runs two token forms side by side, public and private. You can switch your balance between them, and your transactions stay private. ### Core concept Privacy here rests on a **UTXO-based privacy model** with these parts: * **Public tokens** are FT4 tokens, and anyone can see them on chain. * **Private tokens** are cryptographic commitments whose amounts stay hidden. * **Shield operations** turn your public tokens into private commitments. * **Private transfers** send private tokens from one user to another anonymously. * **Unshield operations** turn private tokens back into public ones. Together, these operations add a **confidential transaction layer** above the Chromia blockchain. For each transaction, you decide whether it is public or private. ## Technical architecture ### Multi-layer architecture Three closely connected layers make up the dapp: ### 1. Circom zero-knowledge circuits **Technology stack**: Circom, the PLONK proof system, and Groth16 as a fallback **Key features**: * **PLONK proofs** keep verification efficient. * **Poseidon hashing** supplies cryptography suited to circuits. * **Nullifier generation** stops the same note from being spent twice. * **Commitment schemes** conceal token amounts. ### 2. Rell dapp (blockchain layer) **Technology stack**: [Rell](https://docs.chromia.com/rell/rell-intro), [Chromia Postchain](https://docs.chromia.com/get-started/about/architecture/node/#overview-of-postchain), [FT4 Framework](https://docs.chromia.com/build/ft4/intro/), ZKPGTXModule #### Security features * **ZKP verification**: ZKPGTXModule checks every private operation. * **Double-spending prevention**: the chain records nullifiers and rejects reused ones. * **Input validation**: a commitment can be spent only if it is valid. * **State consistency**: the UTXO sets are kept accurate. ### 3. Next.js client (frontend layer) **Technology stack**: Next.js, React, TypeScript, MetaMask integration, and the Chromia FT4Client **Key features**: * **SecureNoteManager** handles keys and encrypts notes on the client side. * **FT4Client integration** connects the frontend to the blockchain. * **MetaMask wallet connection** authenticates users and signs their transactions. * **ZKP proof generation** happens in your browser through WebAssembly circuits. * **Private key derivation** builds the note-decryption key from a wallet signature. * **A straightforward UI** lets you shield, unshield, and transfer privately. Written for this site from Chromia’s public course. Code samples are the course’s own. [← Previous**Project setup**](https://chromia.com/learn/zero-knowledge-proof/setup/)[Next →**Module 1: Writing Circom circuits**](https://chromia.com/learn/zero-knowledge-proof/circom-circuits/) On this page * [What is the demo dapp?](#what-is-the-demo-dapp) * [Technical architecture](#technical-architecture)