Blockchain based Distributed Storage Networks (Filecoin)

Strawman: put all file datas into the blockchain

• files are too large for everyone to validate
• no incentives for nodes to store and share files
  • storage
  • transmission

Off-chain storage

• How to prove each storage server actually store the data?
  • the verifier cannot store the entire file
• possible attacks
  • not storing the file, generating proofs dynamically
  • sybil attack: pretend to store more copies than actually does
  • outsourcing to external storage
• zero knowledge proof
  • trusted party
    • pk - prove key
    • vk - verification key
  • untrusted storage server
    • given a variable x, generate a proof π
  • anyone with (pk, vk) can verify (x, π)
    • put the (pk, vk) onto the blockchain
• avoid sybil attack
  • seal: multiple rounds of encryption (AES)
• avoid outsourcing attack
  • require the verification to finish within a timeout

Filecoin

• blockchain to store metadata
• blockchain can work as a trusted party (market)
  • bid: Alice -> market
  • ask: Bob -> market
  • deal: Bob -> Alice -> k (within a time bound)

Put procedure

• client: add bid order to L (ledger)
• network: match order, find ask
• client: sign deal, send deal (bid, ask), piece (with pk,vk,aes) to miner (storage server)
• miner: receive deal, piece, store the piece, sign

Get procedure

• on-chain: too much overhead
  • what if the client lies?
    • piece by piece
• off-chain: micropayment
  • signed by client
  • miner will send grouped micropayments to L after the data transfer is over