135 lines
5.1 KiB
Markdown
135 lines
5.1 KiB
Markdown
Codex Contracts
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================
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An experimental implementation of the smart contracts that underlay the Codex
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storage network. Its goal is to experiment with the rules around the bidding
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process, the storage contracts, the storage proofs and the host collateral.
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Neither completeness nor correctness are guaranteed at this moment in time.
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Running
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-------
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To run the tests, execute the following commands:
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npm install
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npm test
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To start a local Ethereum node with the contracts deployed, execute:
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npm start
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This will create a `deployment-localhost.json` file containing the addresses of
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the deployed contracts.
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Overview
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--------
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The Codex storage network depends on hosts offering storage to clients of the
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network. The smart contracts in this repository handle interactions between
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client and hosts as they negotiate and fulfill a contract to store data for a
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certain amount of time.
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When all goes well, the client and hosts perform the following steps:
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Client Host Marketplace Contract
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| --------------- request (1) -------------> |
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| ----- data (2) ---> | |
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| ----- fill (3) ----> |
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| ---- proof (4) ----> |
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| ---- proof (4) ----> |
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| ---- proof (4) ----> |
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| <-- payment (5) ---- |
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1. Client submits a request for storage, containing the size of the data that
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it wants to store and the length of time it wants to store it
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2. Client makes the data available to hosts
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3. Hosts submit storage proofs to fill slots in the contract
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4. While the storage contract is active, host prove that they are still
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storing the data by responding to frequent random challenges
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5. At the end of the contract the hosts are paid
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Contracts
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---------
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A storage contract contains of a number of slots. Each of these slots represents
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an agreement with a storage host to store a part of the data. Hosts that want to
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offer storage can fill a slot in the contract.
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A contract can be negotiated through requests. A request contains the size of
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the data, the length of time during which it needs to be stored, and a number of
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slots. It also contains the reward that a client is willing to pay and proof
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requirements such as how often a proof will need to be submitted by hosts. A
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random nonce is included to ensure uniqueness among similar requests.
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When a new storage contract is created the client immediately pays the entire
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price of the contract. The payment is only released to the host upon successful
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completion of the contract.
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Collateral
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------
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To motivate a host to remain honest, it must put up some collateral before it is
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allowed to participate in storage contracts. The collateral may not be withdrawn
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as long as a host is participating in an active storage contract.
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Should a host be misbehaving, then its collateral may be reduced by a certain
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percentage (slashed).
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Proofs
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------
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Hosts are required to submit frequent proofs while a contract is active. These
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proofs ensure with a high probability that hosts are still holding on to the
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data that they were entrusted with.
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To ensure that hosts are not able to predict and precalculate proofs, these
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proofs are based on a random challenge. Currently we use ethereum block hashes
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to determine two things: 1) whether or not a proof is required at this point in
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time, and 2) the random challenge for the proof. Although hosts will not be able
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to predict the exact times at which proofs are required, the frequency of proofs
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averages out to a value that was set by the client in the request for storage.
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Hosts have a small period of time in which they are expected to submit a proof.
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When that time has expired without seeing a proof, validators are able to point
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out the lack of proof. If a host misses too many proofs, it results into a
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slashing of its collateral.
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References
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----------
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* [A marketplace for storage
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durability](https://github.com/codex-storage/codex-research/blob/master/design/marketplace.md)
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(design document)
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* [Timing of Storage
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Proofs](https://github.com/codex-storage/codex-research/blob/master/design/storage-proof-timing.md)
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(design document)
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To Do
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-----
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* Actual proofs
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Because the actual proof of retrievability algorithm hasn't been determined yet
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we're using a dummy algorithm for now.
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* Contract repair
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Allow another host to take over a slot in the contract when the original
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host missed too many proofs.
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* Reward validators
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A validator that points out missed proofs should be compensated for its
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vigilance and for the gas costs of invoking the smart contract.
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* Analysis and optimization of gas usage
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