Idea: Computation Coin

February 17, 2017

I am posting a draft written during the summer of 2017. I wrote this after reading the Versum paper and starting learning about verifiable computation. The idea here is to do faster off-chain contracts.

Computation Coin (CoCo)

Delegate computations by creating bounties

Motivations

1. Complex contracts are really expensive in Ethereum
2. Every ethereum miner runs every computation (too much waste!)
3. Use ideas from Refereed Multi-prover Delegated Computation (and Versum)
4. SNARK & other systems are too expensive (!!)

Setting

• Users: they want to pay for computation
• Computers: they want to be rewarded for computing
• Trust model: this runs in the any trust model, if there is at least an honest computer running the computation, the computation is run correctly.

Protocols

• ComputationCoin: Users can create computation bounties that Computers can solve.
• ReputationContract: Computers that misbehave are reported to ReputationContract and lose their reputation.

Protocol 1: ComputationCoin Protocol

• CreateComputation(code, timeout, minReputation):

  User writes a computation code (following Versum Guidelines). At timeout time, all the coins in the contract are given to the winning answer. In this contract, only miners with minReputation from ReputationContract can participate.

• FinanceComputation(coins):

  Any user can put coins into the contract to incentivize Computers to compute!

• SolveComputation(ans, comm, coins):

  Computers solve the computation and submit the answers ans, a commitment to the computation history comm, a collateral coins required by the contract, this will be added to the total amount of coins in the contract.

• ConfuteAnswer(ans, comm, coins, conflict):

  Computers can confute a previous answer by submitting their ans, a commitment to their computation history comm, a collateral coins required by the contract and the part of conflict between their answer and the previous submitter answer. (Note: this function call is only going to be added/processed by having the miners running “conflict”)

Protocol 2: ReputationContract Protocol

If a computer is found to create an incorrect computation in the future, they can be referenced to a reputation contract, losing in this way reputation, so in the future Computation contract can set up some minimum reputation they require.

Problems left

• Running arbitrary computation in a contract to detect conflict (this is a technical detail)
• (Actually important) How to keep computation history around and in an accountable way for a long time (they also might be long!!)
• Can we design this into an ethereum contract?
• Game theoretical analysis: what if EVERY computer is incentivized to misbehave?

- Nicola Greco,
Keep on rocking the decentralized web