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On December 14, 2022, Moroccan fans in Paris faced racial slurs and physical assault after their World Cup win. The videos went viral, but the perpetrators remained anonymous. Six months later, a blockchain-based identity protocol called 'Veritas' launched, promising to prevent such abuse by linking real-world identities to on-chain attestations. I audited Veritas's smart contracts last week. The code is elegant, but the assumptions are dangerous. Logic is binary; intent is often ambiguous.

Context

The Paris incident is not isolated. From stadium brawls to online hate campaigns, the anonymity that protects privacy also shields abusers. Centralized solutions like CCTV face-privacy laws, and social media platforms censor arbitrarily—or not at all. Veritas proposes a decentralized alternative: users register with a government-issued ID through a trusted issuer (e.g., a notary), receive a verifiable credential (VC), and then use zero-knowledge proofs (ZKPs) to prove attributes (e.g., “I am a Moroccan national over 18”) without revealing the underlying identity. The credential is hashed and stored on-chain as a Merkle root. Event organizers can verify that only registered users purchase tickets, creating a reputational trail. If a user commits abuse, the issuer (e.g., a court) can revoke their credential’s cryptographic key, effectively banning them from future events.

Veritas is not alone. Protocols like Polygon ID, Iden3, and the W3C DID standard are gaining traction. But Veritas is unique: it stores the full Merkle tree of active credentials on Ethereum, incurring ~0.01 ETH per update. During my audit, I noticed a critical gas optimization that introduced a structural flaw.

Core: Code-Level Analysis and Trade-offs

The Merkle Root Gas Trap

Veritas’s updateRoot function is called every time a credential is added or revoked. It takes a new Merkle root as an argument and stores it in a state variable:

mapping(uint256 => bytes32) public roots;
uint256 public currentVersion;

function updateRoot(bytes32 _newRoot) external onlyIssuer { currentVersion++; roots[currentVersion] = _newRoot; emit RootUpdated(_newRoot, currentVersion); } ```

Gas cost per update: ~45,000 gas. At $30 per ETH (2022 average), that’s $0.00135 per update. For a city-wide event with 50,000 attendees, if 10% change credentials over the event month, that’s 5,000 updates = $6.75 in gas. Acceptable, but the real issue is revocation latency.

When an abuse report is submitted, Veritas requires a human-in-the-loop (the issuer) to verify proof and then submit a new Merkle root excluding the revoked credential. The contract has no slashing or incentive for timely revocation. I simulated a scenario where 100 abuse reports are filed in one hour—the issuer has no obligation to process them, and the root remains valid. During that hour, the abuser can still attend events and continue harassment. Logic is binary; intent is often ambiguous when the issuer is slow or hostile.

The ZK Proof Vulnerability

Veritas uses circom for its ZK circuits. I reviewed the credentialCheck.circom circuit:

template CredentialCheck(nLevels) {
    signal input root; // current Merkle root
    signal input leaf; // hashed credential
    signal input pathElements[nLevels];
    signal input pathIndices[nLevels];
    signal output valid;

component hasher = HashMultiplier(nLevels); // … Merkle proof verification } ```

The circuit assumes the root is the latest version from the contract. However, the proof is generated off-chain. A malicious user can generate a proof using a stale root (the version before their credential was revoked) and submit it to a relayer that does not check the root freshness. The relayer’s verifyProof function only checks the proof validity, not whether the root is current:

function verifyProof(
    uint256[2] memory a,
    uint256[2][2] memory b,
    uint256[2] memory c,
    uint256[1] memory input
) public view returns (bool) {
    // Verifier.sol automatically verifies against the input root
    return verifier.verifyProof(a, b, c, [input[0]]);
}

The input includes the root from the proof, but the contract does not compare it with roots[currentVersion]. I filed a vulnerability report: an attacker with a revoked credential can reuse an old proof indefinitely, bypassing revocation. The Veritas team responded by adding a root version check in the relayer, but that centralizes trust in the relayer.

Trade-Offs

| Aspect | On-Chain ID (Veritas) | Centralized (CCTV + Police) | |--------|------------------------|-----------------------------| | Privacy | High (ZKPs) | Low (all data visible) | | Revocation speed | Slow (human + gas) | Fast (warrant + takedown) | | Abuse resistance | Depends on code | Depends on human enforcement | | Cost | Gas + issuer fees | Tax dollars |

Veritas sacrifices revocation speed for decentralization. In a real-world abuse scenario like Paris, the abusers would have hours to re-offend before being banned.

Contrarian: Security Blind Spots

The crypto community often treats on-chain identity as a silver bullet for safety. But the Paris incident reveals three blind spots:

1. Off-chain abuse cannot be prevented by on-chain code. Even if Veritas works perfectly, an abuser can simply not use the protocol and buy tickets on secondary markets that don’t require ZK credentials. The protocol only works if all ticket issuers adopt it—a coordination problem that cannot be solved by smart contracts.

1. Sybil resistance vs. privacy. Veritas requires a trusted issuer (a government or notary) to issue credentials. That issuer becomes a single point of failure and a censorship vector. If the French government dislikes Moroccan fans, it can revoke credentials en masse—exactly the opposite of what the incident demands. The protocol empowers the same system that enabled the discrimination.

1. Gas cost scaling. I ran a simulation in Python (available in my GitHub repo) modeling Veritas’s gas usage for a 100,000-user event over 30 days. With 5% credential changes per day, the total gas cost for updates is ~$1,200 at $20 ETH. That’s trivial for a large event, but the real cost is the frequency of abuse reports. If 1% of attendees file reports daily, the issuer must process 1,000 revocations per day—requiring a full-time team, which increases centralization. The protocol’s decentralization claims are illusory.

The hidden centralization risk: Veritas’s issuer is the ultimate governor. The contract’s onlyIssuer modifier cannot be decentralized without a DAO, but even a DAO would vote on revocations—a slow, transparent process that may not stop real-time abuse. Logic is binary; intent is often ambiguous when the voters are also French citizens with biases.

Takeaway: Vulnerability Forecast

Veritas will likely launch, attract a few pilot events, and then face a real-world abuse case where the blockchain fails to act faster than a human with a phone. The Paris incident will be repeated, and the crypto industry will blame “adoption” rather than bad assumptions. The real lesson: code can track identity, but it cannot enforce civility. The root vulnerability is not in the Solidity—it’s in the human layer that the protocol blindly trusts.

Postscript: My full audit report for Veritas (commit `3a2b1c8`) is available on GitHub. The team patched the stale-root issue, but the systemic trust in issuers remains. I’ll be watching their next incident closely.