HumanVouch

Proof that a real, unique human stands behind a piece of content — anonymous, sybil-resistant, and verified on Stellar with zero-knowledge.

🔗 Live demo: https://web-seven-eta-40.vercel.app · 🎬 Narrated walkthrough: demo/humanvouch-demo-narrated.mp4

Built for Stellar Hacks: Real-World ZK.

---

The honest thesis

You cannot prove, from content alone, that a human and not an AI wrote it. The bytes are identical, and AI detectors are unreliable and trivially evaded (Google's Dipper paraphraser dropped one detector from 70% → 4.6% accuracy). HumanVouch does not attempt this.

Instead it proves something real and achievable: a verified, unique human privately vouches for a piece of content — putting their (anonymous) personhood behind it, in a way bots and duplicate accounts cannot fake. It's attribution, not authorship; accountability, not AI-detection.

What it does

• Vouch — a verified human stakes a private, anonymous vouch on a piece of content. A Groth16 zero-knowledge proof is generated in the browser (the identity secret never leaves the device) and the attestation is recorded on Stellar.
• Verify — anyone can check how many unique verified humans stand behind a piece of content.
• Shareable credential — vouching returns a /?v=<contentHashField> link (the SHA-256 content hash reduced into the BLS12-381 field, recomputable by anyone holding the content) + a paste-able badge you drop on X, Medium, anywhere; opening it resolves the attestation on-chain.
• For agents (x402) — an HTTP endpoint where an AI agent pays a micropayment over x402 (HTTP 402) and gets a verifiable, on-chain answer to "does a real human stand behind this content?" — HumanVouch as infrastructure for the agent era.
• Proof of personhood — a real Cloudflare Turnstile human check gates getting an identity (anti-bot); production upgrades to World ID for true uniqueness.
• Sybil-resistance — one human, one vouch per content, enforced on-chain by a nullifier.

How the zero-knowledge works

The circuit proves, without revealing the human:

commitment      = Poseidon(identitySecret)
MerkleInclusion(commitment, path) == root        // membership in a personhood registry
nullifierHash   = Poseidon(identitySecret, contentHash)   // one human, one vouch per content

Public signals: [root, nullifierHash, contentHash]. The on-chain AttestContract verifies the Groth16 proof, requires the root be a valid registry root (Groth16 validity alone ≠ membership), rejects nullifier replay, and records the vouch.

On Stellar this means BLS12-381 (Soroban's native pairing). The circuit is compiled with circom --prime bls12381 and hashes with Poseidon over BLS12-381 — a Poseidon-Merkle membership proof verified on Stellar, which (as far as we found) had not been demonstrated before.

On-chain (Stellar testnet)

• AttestContract: CDPDQJB7HX5XVOUHEDQKV6T7KJXNGVTVH3VDCXMFEE7GPIIINOVO5YZT (set_vk, set_root / is_valid_root, attest, get_vouches).
• Built on the official soroban-examples/groth16_verifier (BLS12-381) + CircomStellar's proof encoder.

Architecture

packages/
  zk/          Circom membership + content-nullifier circuit (Poseidon-bls12381) + off-chain witness
  contracts/   Soroban: groth16 verifier + AttestContract (registry + attest + replay guard)
  web/         Nuxt app: built-in wallet, browser proving, verify, shareable links,
               x402 agent endpoint (/api/v1/attestation), Turnstile personhood
  circuits/    Plan-01 circuit lib (BN254, TDD) — superseded on-chain by the bls12381 build
docs/          design spec, BLS12-381 migration addendum, on-chain status

Stack: Circom 2 + snarkjs (Groth16) · Soroban (Rust) on Stellar testnet · Nuxt 3 / Vue + Tailwind · @stellar/stellar-sdk · Cloudflare Turnstile · deployed on Vercel.

Run it

# the full live app
cd packages/web && yarn install && yarn dev      # http://127.0.0.1:58273

# rebuild the ZK circuit + proof (needs the circom 2 compiler on PATH)
cd packages/zk/circuits && mkdir -p build
circom attestation255.circom --r1cs --wasm --prime bls12381 -o build
# trusted setup + proof: see docs/ONCHAIN-STATUS.md

Deploy

The live demo is deployed to Vercel with packages/web/scripts/deploy.sh, the only reproducible deployment path:

cd packages/web && ./scripts/deploy.sh

What the script does:

1. Builds with the Vercel preset (VERCEL=1 yarn build), producing .vercel/output/.
2. Copies the complete @stellar/stellar-sdk package from the root node_modules into every serverless function under .vercel/output/functions/*.func/node_modules/@stellar/stellar-sdk.
3. Uploads the prebuilt output to production with npx --yes vercel deploy --prebuilt --prod --yes.

Do not remove step 2. stellar-sdk 16's ESM build ships nested vendored dependencies that Vercel's file tracer misses. Without the copy, the server routes (for example the x402 endpoint /api/v1/attestation) return a 500 on a missing js-xdr file.

Requirements: the Vercel CLI must be authenticated (npx vercel login, or a VERCEL_TOKEN in the environment) and the directory linked to the Vercel project (npx vercel link).

Honest caveats (also stated in the demo)

• Not AI detection. Attribution to an accountable unique human, not a claim about who typed the bytes.
• Demo trusted setup is non-production (deterministic entropy → forgeable). Production needs a real MPC.
• Personhood is Cloudflare Turnstile (anti-bot) in the demo; production = World ID (unique-personhood).
• The demo personhood registry is operated by us (real Poseidon-bls12381 commitments + Merkle root published on-chain) — real cryptography, standing in for World ID / passport.

---

Real zero-knowledge, real on-chain, for the humans who create — and the agents that increasingly read what we write.