HotPot is a blockchain-based implementation of a 'susu'. While susu's are normally based on the trust among participants (commonly friends or family members), our version is totally trustless. Susus are common in much of the developing world and in Asia.

We developed a smart-contract (hotpot.sol) that is currently depolyed on Rinkeby. Users can join the susu by interacting with the smart contract from a browser with metamask. The contract allows anyone to create a susu or join an existing susu. The creator of a susu using our contract can specify the buy-in amount, the minimum and maximum number of users (so they can bound the odds of each person winning). They also can can configure something called the _internalPools which act as lotteries within the lottery. More internal pools allow for more winners (each getting a proportional piece of the payout), and this reduces variance by increasing the median payout per player per round.

The core of hotpot is a pair of interlocking smart contracts - hotpot.sol and registry.sol. The hotpotRegistry contract is deployed on Rinkeby at 0xE112148658ab6BD8e17DbE42F2935e7a919AfaA9 and contains a list of every instance of hotpot which has been deployed. This makes it easy for frontend applciations to discover existing pools. The registry contract is designed to be deployed once and left. The hotpot contract implements the actual lottery logic. It can be instantiated with a number of different parameters. We've deployed one hotpot instance to Rinkeby, but we expect users to deploy many more instances. For that reason, we've configured the contract to add its own address to the registry on construction. The remaining contracts in contracts implent the Compound Protocol. They are provided to facilitate a future positive-sum implementation of Hotpot - see below for details.

We've also contributed a sketch of a frontend, which can use Metamask to interface with the blockchain. The pages in hotpot-frontend/ support each of the user journies we've identified, but are not yet connected to the Rinkeby backend.

One amazing aspect of running a susu on ethereum is that they money doesn't need to sit idly while it is waiting to get paid out; we can seamlessly interact with other DeFi infrastructure (in this case Compound) to earn interest on the pot until users request their funds from our contract. [Compound withdrawals are not production-ready].

To make our susu trustless, we needed to change more about the normal structure than just to put it on the blockchain. Normally, susu participants rotate in order receiving the payout. However, on the blockchain, this would let a bad actor join the susu right before their slot is scheduled to receive a payout. To combat this, we needed to make the payout schedule unpredictable (similar to a lottery where a participant is chosen at random).

1. (IMPORTANT) Modify Hotpot to use a secure RNG! Do not deploy on mainnet without it! BLS Threshold signatures are coming to ETH - those will be suitable for this sort of application once they are deployed. Otherwise, try Pentagonal Exchange https://medium.com/@preston.b.evans/pentagonal-exchange-90225f2489c8. Do not, I repeat do not attempt to use the current scheme (blockhashes) or RANDO to decide lotteries for real money.
2. Connect frontend to backend.
3. Deploy on mainnet
4. Port to Ethermint for lower transaction fees
5. Port to Celo and integrate and market in developing economies