Intro

This repo contains the code of fair exchange protocol described in "FairDrop: a Confidential Fair Exchange Protocol for Media Workers"

Prerequisite

Client applications require web3.py and PyNaCl, that can be installed via pip install web3 PyNaCl. The prototype uses Infura API to connect Ethereum network, and a API key is already provided inside the client/data/settings.json file.

Installation

Clone git repository git clone https://github.com/EgonGalvani/confidential-fair-exchange.git

Smart contract

The smart contract is defined inside the contracts/conf-fair-exchange.sol file. We already provide a version of the smart contract deployed in the Ropsten network, at the address indicated inside the client/data/settings.json file. In any case the following sections explain how to compile and deploy a new version of the smart contract.

Compilation

After each modification to the code of the smart contract, it has to be compiled again. We used etherlime to compile it, but any other tool can be used. The compiled file has to be placed inside the build directory, and renamed ConfidentialFairExchange.json. For using etherlime the following steps are required:

• first, install it via npm install -g etherlime
• then, from the root directory of the project, execute etherlime compile, the compiled file will be automatically created in the build directory

Deployment

To deply the smart contract, the script client/deployer.py can be used. It deploys the smart contract inside the Ropsten testnet and it creates the client/data/settings.json file. This file contains the rpc url used for the communication with the blockchain, the contract address and other information about the wallets used by the scripts.

Offline data generation

To create some sample data for testing, the client/offline_data_generator.py script can be used. It creates two files inside the data repository:

• shared.json that contains the information regarding the files that is shared publicly
• master_keys.json that contains the master keys associated to each file

Usage

We provide two main scripts: client/seller.py and client/buyer.py, that as the names suggest, allow to manage operations for seller and buyer respectively. Both scripts provide a simple user interface that allows to easily interact with the smart contract. Example of usage:
https://user-images.githubusercontent.com/27569184/190029652-9307432c-08da-4316-8082-6d508c679286.mp4

Settings

The file client/data/settings.json contains all the settings used by the scripts.

Change wallets

To modify the private key of the wallets associated to seller or buyer, it is necessary to modify the corresponding fields inside the settings file. Also, in case of future deploys, it is necessary to modify the lines 43, 44, 45 in the deployer.py script.

Change network

The scripts communicate with the network via a provider variable, that is usually initialized at the beginning of each file. If you want to modify the rpc url used, then it is possilble to do it by modifying the settings.json file. Otherwise, if you want to change the provider type, it is necessary to modify:

• lines 25/26 of seller.py
• lines 25/26 of buyer.py
• in the case of new deploy, lines 10/11/12 of deployer.py