Interview Challange

See challenge.md for problem definition.

The solution presented here can be broken into four pieces. First, the devchain/ directory contains the configuration and setup to run a private, local blockchain with three participating nodes. Next a smart contract resides in store-contract/ as a truffle project. This contract is deployed to the local chain. Lindell's blockchain-crypto-mpc library is used to run EDDSA signatures via MPC for two parties. This process is managed by coordinator.sh in coordinator/. Finally, the coordinator will upload the signature to the deployed contract via the web3 client in the chain-bridge/ directory.

Environment

The following build instructions are for Ubuntu 18.04LTS but will likely work with little modification on other debian-based operating systems.

First Run Setup

0. Ensure submodules have been pulled.

git submodule init

1. Install crypto library dependencies and build.

make deps

2. Follow the instructions in devchain/README.md.

3. Deploy the truffle contract.

cd store-contract
truffle deploy --network devchain

4. Install node packages for chain-bridge

cd chain-bridge
npm install

Run

./devchain/start.sh
./alice/alice.sh pay carol $5
./bob/bob.sh pay carol $5

Note to stop the devchain run ./devchain/stop.sh

Note: both alice and bob have the ability to fake a signature using an incorrect key shard. Passing the -f flag to the script enables this behavior. Unfortunately the blockchain-crypto-mpc library crashes when doing this.

Verify Signature

./verify/verify.sh pay carol $5

The verify script will pull the signature from the chain and verify with the message passed in as an argument.