NoirZeppelin - OpenZeppelin-Style Privacy Library for Noir

[stawuah]

Problem

NoirZeppelin is a comprehensive, production-ready privacy library for the Noir programming language that ports battle-tested OpenZeppelin contract patterns into zero-knowledge circuits. This library enables developers to build privacy-preserving applications for both Web2 and Web3 environments without requiring deep cryptographic expertise.

The library standardizes common privacy patterns (authentication, access control, token operations, voting) while maintaining the security guarantees of zero-knowledge proofs. It aims to become the industry standard for privacy-preserving circuit development in Noir.

Current Challenges

1. Lack of Standardized Privacy Patterns: Developers building ZK applications must reinvent privacy primitives from scratch, leading to security vulnerabilities and inefficient code.

2. High Barrier to Entry: Understanding cryptographic proofs requires specialized knowledge. There's no "OpenZeppelin equivalent" for Noir that abstracts complexity.

3. Code Reusability: No established library pattern for privacy circuits. Each project siloes its implementation, wasting effort and creating maintenance burden.

4. Security Inconsistency: Without audited reference implementations, privacy bugs proliferate. Different projects implement the same concepts differently, reducing auditability.

5. Bridge Gap Between Web2 and Web3: Privacy needs exist in both centralized and decentralized applications, but Noir lacks tooling to serve both ecosystems simultaneously.

6. Verification Complexity: Integrating ZK proofs with smart contracts requires manual Solidity verifier generation and testing. This process is error-prone.

Why Now?

Noir is gaining adoption (Aztec Contracts, Solidity integration, NoirJS)
Industry recognizes privacy as critical infrastructure
OpenZeppelin's success proves developers will adopt standardized libraries
Web3 needs privacy solutions; Web2 seeks regulatory-compliant authentication

Happy Case

Core Vision

Create an audited, production-ready library that:

• Ports OpenZeppelin's most critical functions to Noir circuits
• Works seamlessly with both Web2 backends and Web3 smart contracts
• Provides clear security patterns and best practices
• Reduces development time and security risk
• Establishes Noir as the standard for privacy-preserving applications

1. Access Control Module

Ported from: OpenZeppelin's AccessControl.sol and Ownable.sol

Functions

• verify_role() - Prove user has a specific role without revealing identity
• verify_multisig() - Prove M-of-N signatures for governance
• verify_permission() - Check permissions against a Merkle tree of privileges
• verify_ownership() - Prove ownership of a resource

Sample Implementation

// Prove user has admin role without revealing identity
pub fn verify_role(
    user_commitment: Field,
    role: Field,
    role_commitment: Field,
    salt: Field
) -> bool {
    // User commitment hides actual identity
    // Prove: hash(user_commitment + role + salt) == role_commitment
    let computed = std::hash::poseidon::bn254::hash_3([user_commitment, role, salt]);
    computed == role_commitment
}

// Prove M-of-N multisig without revealing which signers
pub fn verify_multisig<N>(
    signers: [Field; N],
    threshold: u32,
    message_hash: Field,
    signatures: [Field; N]
) -> bool {
    let mut valid_count = 0;
    for i in 0..N {
        // Check if signature is valid for this signer
        if signatures[i] == std::hash::poseidon::bn254::hash_2([signers[i], message_hash]) {
            valid_count += 1;
        }
    }
    valid_count >= threshold
}

Use Cases

• Web3: Private governance systems (DAO voting without revealing voter identity)
• Web2: Role-based authentication (access corporate systems without exposing roles)

---

2. Authentication Module

Ported from: OpenZeppelin's ERC721Permit.sol, ERC2612.sol patterns

Functions

• prove_secret_knowledge() - Prove you know a secret without revealing it
• verify_password() - Verify a password against a salted hash (for Web2 apps)
• verify_2fa() - Time-window-based OTP verification
• prove_ownership_key() - Prove control of a private key/account
• sign_and_verify() - Fiat-Shamir-based signature verification

Sample Implementation

// Verify password without transmitting plaintext
pub fn verify_password(
    password: Field,
    password_hash: Field,
    salt: Field
) -> bool {
    let computed_hash = std::hash::poseidon::bn254::hash_2([password, salt]);
    computed_hash == password_hash
}

// Time-based OTP verification (Google Authenticator style)
pub fn verify_2fa(
    otp: Field,
    otp_secret: Field,
    timestamp: u64,
    window_size: u64
) -> bool {
    let time_window = timestamp / window_size;
    
    // Check current window
    let current_otp = std::hash::poseidon::bn254::hash_2([otp_secret, time_window as Field]);
    
    // Also check previous window (clock drift tolerance)
    let previous_otp = std::hash::poseidon::bn254::hash_2([otp_secret, (time_window - 1) as Field]);
    
    (otp == current_otp) | (otp == previous_otp)
}

// Prove knowledge of secret without revealing it
pub fn prove_secret_knowledge(
    secret: Field,
    secret_hash: Field,
    challenge: Field,
    response: Field
) -> bool {
    // Verify the secret matches the commitment
    let secret_valid = std::hash::poseidon::bn254::hash_1([secret]) == secret_hash;
    
    // Verify the challenge-response (Fiat-Shamir)
    let response_valid = response == std::hash::poseidon::bn254::hash_2([secret, challenge]);
    
    secret_valid & response_valid
}

Use Cases

• Web2: Privacy-first authentication systems (passwords never sent in plaintext to server)
• Web3: Non-interactive proof of account ownership for airdrops or whitelists

---

3. Token Operations Module

Ported from: OpenZeppelin's ERC20.sol, ERC721.sol, ERC1155.sol

Functions

• prove_token_balance() - Prove you own tokens without revealing amount
• prove_transfer_valid() - Prove a transfer is valid (sufficient funds, proper permissions)
• prove_token_spending() - Anonymous token spending with nullifiers (prevent double-spend)
• verify_nft_ownership() - Prove ownership of an NFT without revealing which one
• prove_batch_transfer() - Verify multiple transfers without revealing amounts

Sample Implementation

// Prove sufficient balance for transfer without revealing amount
pub fn prove_transfer_valid(
    sender_balance: Field,
    transfer_amount: Field,
    sender_balance_commitment: Field,
    salt: Field
) -> bool {
    // Verify commitment matches actual balance
    let commitment_valid = std::hash::poseidon::bn254::hash_2([sender_balance, salt]) == sender_balance_commitment;
    
    // Verify sufficient funds (without revealing exact amount)
    let sufficient_funds = sender_balance >= transfer_amount;
    
    // Verify amount is positive
    let positive_amount = transfer_amount > 0;
    
    commitment_valid & sufficient_funds & positive_amount
}

// Anonymous token spending with nullifier (prevents double-spend)
pub fn prove_token_spending<let TREE_DEPTH: u32>(
    token_serial: Field,
    amount: Field,
    recipient: Field,
    token_root: Field,
    merkle_proof: [Field; TREE_DEPTH],
    nullifier: Field,
    nullifier_secret: Field
) -> bool {
    // Create token commitment
    let token_commitment = std::hash::poseidon::bn254::hash_3([token_serial, amount, recipient]);
    
    // Prove token is in the set (Merkle proof)
    let in_set = verify_merkle_proof(token_commitment, 0, merkle_proof, token_root);
    
    // Verify nullifier is correctly generated (prevents double-spend)
    let expected_nullifier = std::hash::poseidon::bn254::hash_2([nullifier_secret, token_serial]);
    let nullifier_valid = nullifier == expected_nullifier;
    
    in_set & nullifier_valid
}

// Prove you own tokens above threshold without revealing exact amount
pub fn prove_token_balance(
    balance: Field,
    min_required: Field,
    balance_commitment: Field,
    salt: Field
) -> bool {
    // Verify commitment
    let commitment_valid = std::hash::poseidon::bn254::hash_2([balance, salt]) == balance_commitment;
    
    // Prove balance meets minimum (range proof concept)
    let meets_minimum = balance >= min_required;
    
    commitment_valid & meets_minimum
}

Use Cases

• Web3: Private DeFi transactions (swaps without front-running via MEV hiding)
• Web3: Anonymous payments where recipient is public but amounts are hidden
• Web2: Privacy-preserving micropayments or credit systems

---

4. Voting & Governance Module

Ported from: OpenZeppelin's Governor.sol patterns

Functions

• prove_valid_vote() - Prove you're eligible to vote and cast a valid vote
• prove_vote_tally() - Aggregate votes without revealing individual votes
• verify_voter_eligibility() - Merkle-tree based voter registry check
• prevent_double_voting() - Nullifier-based replay protection

Sample Implementation

// Prove valid vote with eligibility and replay protection
pub fn prove_valid_vote<let TREE_DEPTH: u32>(
    voter_id: Field,
    vote: u32,
    vote_commitment: Field,
    voters_root: Field,
    voter_merkle_proof: [Field; TREE_DEPTH],
    salt: Field
) -> bool {
    // Vote must be valid (0 = No, 1 = Yes)
    let valid_vote = (vote == 0) | (vote == 1);
    
    // Prove voter is in eligible voters registry
    let voter_commitment = std::hash::poseidon::bn254::hash_2([voter_id, salt]);
    let valid_voter = verify_merkle_proof(
        voter_commitment,
        0,
        voter_merkle_proof,
        voters_root
    );
    
    // Verify vote commitment matches
    let commitment_matches = vote_commitment == 
        std::hash::poseidon::bn254::hash_3([voter_id, vote as Field, salt]);
    
    valid_vote & valid_voter & commitment_matches
}

// Generate nullifier to prevent double voting
pub fn prevent_double_voting(
    voter_secret: Field,
    proposal_id: Field
) -> Field {
    // Nullifier uniquely identifies this voter+proposal combination
    // Prevents same voter from voting twice on same proposal
    std::hash::poseidon::bn254::hash_2([voter_secret, proposal_id])
}

// Verify voter eligibility via Merkle proof
pub fn verify_voter_eligibility<let TREE_DEPTH: u32>(
    voter_id: Field,
    voters_root: Field,
    merkle_proof: [Field; TREE_DEPTH],
    index: u32
) -> bool {
    verify_merkle_proof(voter_id, index, merkle_proof, voters_root)
}

Use Cases

• Web3: Private governance (voting without revealing your stance)
• Web2: Private surveys/polls (aggregated results without individual responses)

---

5. Merkle Proof Module

Core utility for all privacy patterns

Functions

• verify_merkle_proof() - Standard Merkle proof verification
• verify_merkle_batch() - Prove membership in multiple trees
• update_merkle_path() - Generate proofs for dynamic trees

Sample Implementation

// Standard Merkle proof verification
pub fn verify_merkle_proof<let TREE_DEPTH: u32>(
    leaf: Field,
    index: u32,
    sibling_path: [Field; TREE_DEPTH],
    root: Field
) -> bool {
    let mut computed = leaf;
    
    for i in 0..TREE_DEPTH {
        // Check if we're on left or right branch
        if (index >> i) & 1 == 1 {
            // We're on the right, sibling is on left
            computed = std::hash::poseidon::bn254::hash_2([sibling_path[i], computed]);
        } else {
            // We're on the left, sibling is on right
            computed = std::hash::poseidon::bn254::hash_2([computed, sibling_path[i]]);
        }
    }
    
    computed == root
}

// Prove membership in multiple Merkle trees (batch verification)
pub fn verify_merkle_batch<let N: u32, let TREE_DEPTH: u32>(
    leaves: [Field; N],
    indices: [u32; N],
    sibling_paths: [[Field; TREE_DEPTH]; N],
    roots: [Field; N]
) -> bool {
    let mut all_valid = true;
    
    for i in 0..N {
        let valid = verify_merkle_proof(
            leaves[i],
            indices[i],
            sibling_paths[i],
            roots[i]
        );
        all_valid = all_valid & valid;
    }
    
    all_valid
}

// Generate nullifier for Merkle tree membership (privacy-preserving)
pub fn generate_merkle_nullifier(
    leaf: Field,
    nullifier_secret: Field
) -> Field {
    std::hash::poseidon::bn254::hash_2([leaf, nullifier_secret])
}

Use Cases

• Efficient membership proofs for whitelists, token registries, voting rolls
• Anonymous credential systems
• Private airdrop claims

---

Summary

NoirZeppelin brings the OpenZeppelin developer experience to privacy-preserving applications. Just as OpenZeppelin made smart contract development accessible and secure, NoirZeppelin makes zero-knowledge proof development simple and safe.

Developer Experience:

• Simple API: Import functions like verify_password() or prove_token_balance() - no cryptography PhD required
• Copy-paste ready: Production-ready circuits that work out of the box
• Universal compatibility: Same code works for Web2 backends and Web3 smart contracts
• Fast integration: Go from idea to working privacy app in hours, not weeks

Key Benefits:

• Security by default: Audited, battle-tested patterns prevent common ZK vulnerabilities
• Reduced development time: 10x faster than building privacy circuits from scratch
• Lower risk: No need to reinvent cryptographic primitives - use proven patterns
• Privacy without complexity: Abstract away circuit details, focus on your application logic

Impact:
NoirZeppelin establishes Noir as the standard for privacy-preserving applications, enabling developers to build with confidence whether they're creating private authentication systems, confidential DeFi protocols, or anonymous voting platforms.

With NoirZeppelin, privacy becomes a feature you can add, not a mountain you have to climb. (NOIR GUD 👽)

Alternatives Considered

Alternative 1: Roll Your Own

Pros: Full control, custom optimization
Cons:

• High security risk (no audits)
• Months of development time
• No community support
• Maintenance burden

Alternative 2: Use Aztec.nr

Pros: Mature, well-tested
Cons:

• Aztec-specific (not general purpose)
• Limited Web2 support
• Tightly coupled to Aztec network
• Not modular enough for standalone use

Alternative 3: Port from Circom

Pros: Existing implementations
Cons:

• Different language paradigm
• Manual porting required
• Not idiomatic Noir
• No Noir-specific optimizations

Why NoirZeppelin is Better

Additional Context

Why This Matters
For the Noir Ecosystem

Accelerates Adoption: Lower barrier to entry for privacy apps
Security: Audited reference implementations reduce vulnerabilities
Standardization: Industry-standard patterns for privacy circuits
Documentation: Clear examples and best practices

For Developers

Time Savings: Stop reinventing the wheel
Security: Built on battle-tested cryptographic patterns
Flexibility: Works with any Noir backend (Barretenberg, Marlin, etc.)
Dual Use: Same library for Web2 and Web3

NoirZeppelin - Implementation Roadmap

Phase 1: MVP (Months 1-2)

Core Deliverables:

• Core cryptography module (Poseidon hashing, Merkle proofs)
• Authentication module (password verification, 2FA)
• Access control module (role verification, multisig)
• Basic documentation and examples
• Unit tests for all functions
• Security audit (external)

---

Phase 2: Extended (Months 3-4)

Core Deliverables:

• Token operations module (balance proofs, transfers)
• Voting module (eligible voter proofs, tallying)
• Nullifier registry utilities
• Performance optimizations
• Integration tests with smart contracts
• Comprehensive API documentation

---

Phase 3: Ecosystem (Months 5-6)

Core Deliverables:

• NoirJS integration examples
• Solidity verifier generation (automated)
• Web2 backend examples (Node.js, Python)
• Best practices guide for circuit auditing
• CLI tool for generating circuits
• Mainnet-ready examples

---

Security Considerations

Threat Model

1. Proof Forgery

• Risk: Ensure only valid proofs are accepted
• Mitigation: Standard Noir verification + external audits

2. Replay Attacks

• Risk: Prevent reuse of valid proofs
• Mitigation: Nullifiers, timestamps, nonces

3. Information Leakage

• Risk: Prevent side-channel attacks
• Mitigation: Constant-time operations, input validation

4. Circuit Vulnerabilities

• Risk: Logic errors in proof generation
• Mitigation: Formal verification, thorough testing, expert audits

---

Audit Plan

Internal:

• Code review by Noir experts

External:

• Security firm (Trail of Bits, OpenZeppelin, Certora)

Community:

• GitHub security policy
• Bug bounty program

Formal Verification:

• Critical functions formally verified

Would you like to submit a PR for this Issue?

Yes

Support Needs

NoirZeppelin - Support Needs

Looking for support from the community in these areas:

1. Technical Review

• Code review of circuit implementations
• Security pattern validation
• Performance optimization suggestions
• Best practices for Noir library structure

---

2. Security Audit

• Connections to auditing firms (Trail of Bits, OpenZeppelin Security, Certora)
• Pre-audit security review by Noir core team
• Formal verification guidance
• Bug bounty program setup

---

3. Documentation

• API documentation standards for Noir libraries
• Example application patterns
• Integration guides (NoirJS, Solidity)
• Tutorial content

---

4. Community

• Feedback on API design decisions
• Real-world use case validation
• Testing on different backends (Barretenberg, Marlin)
• Promotion in Noir ecosystem channels

---

5. Ecosystem Integration

• Official Noir documentation inclusion
• Awesome-noir listing
• Conference/meetup presentation opportunities
• Collaboration with Aztec team on patterns