Building a Zero-Knowledge Proof dApp on Concordium

In this tutorial, you’ll learn how to integrate Concordium’s browser and mobile wallets into a React-based decentralized application (dApp), and generate zero-knowledge (ZK) proofs.

Concordium is an identity-based blockchain with a unique approach to balancing privacy and compliance. Through wallets, users can generate zero-knowledge proofs and selectively disclose identity attributes on their accounts like nationality, age, etc., instead of sharing the entire ID information.

Concordium wallets serve a unique dual purpose compared to wallets on other blockchains. They not only hold accounts (blockchain addresses) but also manage identities. Users first create an identity in their wallet by completing a verification process with an identity provider (using a passport or ID card). Then, they can create on-chain accounts through a transaction that associates each account with their verified identity.

Unlike other blockchains where addresses exist without any identity context, Concordium accounts are explicitly linked to real-world identities. This architecture enables wallets to generate zero-knowledge proofs about the identity information associated with a user’s account, allowing for selective disclosure of attributes in a self-sovereign way.

Unlike many other blockchains where implementing zero-knowledge proofs requires deep cryptographic expertise, Concordium simplifies this process significantly:

1. Built-in identity layer: Identity credentials are already associated with accounts, read this article for more details

2. Wallet-managed proofs: The cryptographic heavy lifting happens in the wallet

3. Flexible proof types: Support for revealing attributes, range proofs, and set membership proofs, read this article for more information

4. Simple developer experience: No need for specialized ZK languages or custom implementations

This architecture allows developers to focus on defining what needs to be proven rather than implementing complex cryptography.

What you will learn

In this tutorial, you will:

• Create a flexible wallet connection interface supporting both browser and mobile wallets

• Define various types of zero-knowledge proof statements

• Generate secure, time-limited challenges for ZK proofs

• Request identity proofs from Concordium wallets

• Process and display the results of these proofs

By the end, you’ll understand how to build privacy-preserving applications that can verify user eligibility while minimizing data exposure - a perfect balance of compliance and privacy.

Note

This tutorial focuses primarily on wallet integration and ZK proof generation from the frontend perspective. While we discuss verification concepts and security considerations throughout, the implementation of a secure backend verification system is not covered in detail.

In a production environment, proper verification of ZK proofs on a secure backend is critical to ensure:

1. The cryptographic proofs are mathematically valid

2. The challenge used in the proof is recent (using block hash verification)

3. The challenge has not been used in a previous proof (preventing replay attacks)

4. All other application-specific requirements are met

For backend implementation details, we reference the compliant-reward-distribution dApp and the web3id-verifier which demonstrate a more complete verification flow. We recommend studying that example alongside this tutorial for more comprehensive understanding.