ProofTrail

Prooftrail is an onchain platform for product ownership, invoices, and transfers, built on Flow Blockchain.

today, when products change hands, the trail of invoices and ownership records is fragile. pdf invoices can be forged, ownership transfers often lack proof, and audit trails break after the first sale. buyers are left guessing, sellers can’t build trust, and auditors struggle to verify authenticity.

prooftrail solves this by making every step verifiable onchain:

a product starts with a unique onchain id. the first sale registers ownership and stores an invoice on lighthouse. the json form of that invoice is hashed and anchored onchain. every resale creates a new invoice plus a transfer certificate. both buyer and seller must sign the certificate onchain before the transfer is valid. the audit trail never resets. all invoices, transfer certificates, and signatures are linked to the product id, forming a complete, tamper-proof history.

my approach balances cost and transparency: invoices live on decentralized storage (lighthouse), while hashes and metadata are onchain for immutability. this creates a low-cost, high-trust system that works for any product lifecycle.

why it matters:

• for luxury goods, provenance and resale markets.
• for supply chains, transparent product journeys.
• for digital + physical assets, seamless transfer of trust.

how we built it:

next.js, tailwindcss, and shadcn/ui for fast, clean frontend.

rainbowkit and wagmi for wallet integrations.

solidity smart contracts on an evm chain for product registry, invoices, and transfer certificates.

lighthouse for decentralized invoice storage.

I built it’s as a framework for trust — a way to give every product a blockchain passport, where invoices and transfers are permanently recorded, signed, and verifiable.

I built prooftrail by combining evm smart contracts with decentralized storage.

frontend: next.js, tailwindcss, shadcn for ui. rainbowkit + wagmi for wallet connections and onchain signing.

contracts: solidity contracts handle product registration, invoice logging, and transfer certificates (buyer + seller must both sign before ownership changes).

storage: invoices are stored as pdfs on lighthouse. their json form is hashed and written onchain, giving us low-cost but immutable records. (also used NEON DB in some areas of storage)

flow (EVM) blockchain: seller uploads invoice → pdf to lighthouse, hash to chain → on resale, new invoice + transfer cert generated → both parties sign → audit trail updates automatically.

using lighthouse kept storage decentralized and affordable, while the onchain hashes made the system tamper-proof.