BuildProof
Verifiable, tamper-evident attestations for legal documents and AI-generated legal outputs: multi-party wallet signatures on-chain (EIP-712, gasless relay), deterministic pre-signing checks, and a pay-per-verify API for AI agents (x402).
Built for the BLI Legal Tech Hackathon 2, tracks LegalTech & RegTech and AI x Blockchain.
Status: prototype, unaudited. The registry, the verify page and the paid x402 API run on Base mainnet, but every record there is a demo with synthetic documents and there are no external users yet; see Live on Base. Every transaction the CLI sends carries BuildProof's Base Builder Code (ERC-8021).
Check it in 2 minutes
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Open the verify page: https://ttimesai-star.github.io/buildproof/ and use the three buttons under Try it in one click. Each one downloads a sample file, hashes it in your browser and looks the hash up on Base mainnet:
- Signed acceptance act:
Attested by all 2 signers and Signers match your list, with registration and completion times from the chain;
- Same act, one amount changed (23,600.00 → 28,600.00, one byte):
Not found;
- AI legal review, approved by a human: an AI-output manifest that became
ATTESTED only after the human reviewer co-signed.
You can also drop any of your own files there: nothing is uploaded, only the hash is sent to the RPC node.
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Watch the demo video (2 min 47 s, narrated): demo.mp4.
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Ask the paid API as an agent would (no wallet needed to see the price):
curl -i https://buildproof-x402.zbignevich.workers.dev/v1/attestation/0x5ce4d8327a23f4fa5c5e0bcc551f22ecc9285b36b5aab25eb4b9093ac92db006
# HTTP/1.1 402 Payment Required + PAYMENT-REQUIRED header: 10000 units of USDC (= $0.01) on Base (eip155:8453)
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Check the contract: Basescan and Sourcify exact match of contracts/BuildProofRegistry.sol.
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Run everything locally (Foundry, Node 18+, Python 3.10+): bash scripts/demo.sh for the 10-step story on a local chain, npm test for all tests. CI runs both on every push.
Why it matters legally
Disputes over documents are usually not about what the law says but about which file is the one the parties agreed to. US evidence rules already accept a matching hash as the ordinary way to show that a copy is identical to the original, and the main e-signature laws do not deny legal effect to electronic records. BuildProof turns that into a shared, timestamped record that every party can check without trusting the others.
- US Federal Rules of Evidence, Rule 902(14) makes data copied from an electronic file self-authenticating when it is "authenticated by a process of digital identification", certified by a qualified person. The Advisory Committee note: "data copied from electronic devices, storage media, and electronic files are ordinarily authenticated by 'hash value'... If the hash values for the original and copy are different, then the copy is not identical to the original." BuildProof records which hash each party approved and when; the certification itself is still done by a person.
- US ESIGN Act, 15 U.S.C. § 7001(a)(1): a signature, contract or other record "may not be denied legal effect, validity, or enforceability solely because it is in electronic form". Arizona, A.R.S. § 44-7061(A)-(B): a signature or record "secured through blockchain technology" is an electronic signature or electronic record.
- EU eIDAS Regulation (EU) No 910/2014, Article 25: an electronic signature "shall not be denied legal effect and admissibility as evidence in legal proceedings solely on the grounds that it is in an electronic form or that it does not meet the requirements for qualified electronic signatures"; only a qualified electronic signature has the effect of a handwritten one (Art. 25(2)).
What this means for BuildProof, stated plainly: a wallet signature is an ordinary electronic signature, not a qualified one (QES). Use BuildProof as the evidence and audit layer next to whatever signature the contract or local law requires, not instead of it. This is a description of the product, not legal advice for any jurisdiction.
Legal use cases
BuildProof provides an immutable, hash-only audit trail and multi-party attestation layer for legal and compliance operations. Content remains private off-chain while party approval and document lineage are proven on-chain.
- Contract and amendment chains (
supersededBy): Main contracts linked to supplementary agreements; once an amendment is attested, the original record shows as superseded.
- NDAs and engagement letters: Multi-party execution via wallet transactions or gasless EIP-712 signatures.
- Acceptance acts and invoices: Pre-signing checks verify arithmetic, rates, cumulative volumes, and party details before registration.
- AI-generated legal outputs: A canonical manifest combines model ID, prompt SHA-256, input document SHA-256 array, and output SHA-256. Co-signed by an AI operator and a human reviewer, it proves which exact output a lawyer approved and guarantees it was not edited afterwards.
- Evidence bundles for disputes and arbitration: Timestamped SHA-256 fingerprints recorded on-chain while sensitive evidence files remain strictly private.
- KYC and compliance file custody: Hash-only proof of file state at a point in time without putting personal data on-chain.
BuildProof complements legally required signatures and serves as tamper-evident evidence layer; see Legal Weight for regulatory scope.
This is the beginning of the README. Read the rest at the original. Read the full README ↗
