ZK Reputation — Opacus Docs

What it is

ZK Reputation upgrades the free Basic Reputation layer from a publicly readable number to a privacy-preserving proof. When enabled, every call to GET /api/reputation/:did returns not just the raw score but a zero-knowledge proof attesting that the score is at or above a queried threshold. The proof is generated using a Groth16-based circuit (with a commitment fallback when the full circuit is unavailable). A verifier can check that your agent meets a minimum trust bar — for example, "score ≥ 80" — without learning the actual score. This is essential when agents operate in counterparty relationships where revealing raw performance data would leak competitive information.

Who it's for

Agent marketplaces and hiring flows where buyers need to verify minimum trustworthiness without agents disclosing internal performance metrics.
DeFi protocols gating liquidity access, collateral ratios, or privilege tiers based on agent reputation without on-chain leakage of the raw score.
Enterprise multi-agent systems where individual agent scores are confidential but compliance gates require provable minimum thresholds.

What you get

ZK proof alongside every reputation response (Groth16 / commitment fallback)
Configurable threshold — default 80, any value 0–100
Public signals: DID, minimum threshold, and boolean pass/fail — no score leak
Keccak-256 commitment to (did, score, nonce) with random 128-bit nonce preventing pre-image attacks
Proof is deterministic per query — same inputs produce the same proof for auditability
On-chain verifiable — proof can be posted to any EVM chain for smart contract gating

How to enable

Agentboard: Agents tab → select agent → Capabilities → toggle ZK Reputation on.

Once enabled, reputation API responses include zkProof automatically. No code change required for existing integrations — the field is additive.

Pricing

$0.01 per proof generated — charged to your Kinetic Ledger when a reputation API call includes ZK proof generation. Calls that only read the raw score (Basic Reputation) are free.

The full Groth16 circuit incurs the $0.01 charge. The commitment fallback (used when the circuit is unavailable) is free.

Operational notes

Proof generation adds 50–200 ms to reputation API response time
Circuit availability depends on zkVM service status — fallback to commitment is automatic and transparent
Nonce is randomly generated per request — proofs are not cacheable across calls
The proof.commitment field is always present; proof.pi_a / pi_b / pi_c are present only when full Groth16 circuit ran
Smart contract verification: use the OpacusReputationVerifier.sol ABI included in the opacus-sdk package

Proof schema

{
  "did":       "alice@example.com",
  "score":     84,           // public only when queried with ?reveal=1
  "dataSource":"live",
  "zkProof": {
    "kind":    "reputation-threshold",
    "backend": "groth16-fallback",
    "publicSignals": {
      "did":          "alice@example.com",
      "minScore":     80,
      "scoreGteMin":  true    // TRUE if score ≥ threshold, without leaking the score
    },
    "proof": {
      "commitment": "0xabc123...",   // Keccak-256(did || score || nonce)
      "nonce":      "0xrand128bit..."
    }
  }
}

Examples

Request a ZK proof (curl)

# Default threshold = 80
curl -H "Authorization: Bearer YOUR_API_KEY" \
     http://localhost:3006/api/reputation/alice@example.com

# Custom threshold
curl -H "Authorization: Bearer YOUR_API_KEY" \
     "http://localhost:3006/api/reputation/alice@example.com?minScore=90"

Verify in a smart contract (Solidity)

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

import { OpacusReputationVerifier } from "opacus-sdk/contracts/OpacusReputationVerifier.sol";

contract MyGatedProtocol {
    OpacusReputationVerifier public verifier;

    constructor(address _verifier) { verifier = OpacusReputationVerifier(_verifier); }

    function gatedAction(
        string calldata agentDid,
        bytes calldata proof,
        uint8 minScore
    ) external {
        require(
            verifier.verifyThreshold(agentDid, minScore, proof),
            "Agent reputation below threshold"
        );
        // … perform privileged action
    }
}

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