Local Ethereum blockchain to store document hashes

Setting up and using a local Ethereum blockchain to store document hashes.

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Table of Contents

• About the project
• Getting Started
  • Prerequisites
  • Project setup
  • Installation
• License

About the project

This is a sample project for storing and reading document hashes from / to the Ethereum blockchain.

Important

This project is for testing purpose only.

The smart contract is not intended to be deployed on the Ethereum main network.

You may also take a look at the eth-hash-app project to interact with the blockchain using Java.

Getting started

Prerequisites

You will need the following tools to create / run the project :

• NodeJS & NPM
• Truffle
• Ganache
• Solidity plugin for Intellij (nice to have)

To install Truffle : npm install -g truffle

Project setup

Command line

• Create new empty Intellij project (i.e. eth-hash-chain)

• Navigate to the project directory : cd C:\Git\eth-hash-chain

• Initialize Truffle project (this creates various directories and files) : truffle init

• Create a new Solidity file (Diploma.sol) in the contracts directory, which will hold our smart contract : truffle create contract Diploma

  Minimal contract code :

  pragma solidity ^0.8.0;
  
  contract Diploma {
      struct Record {
          uint mineTime;
          uint blockNumber;
      }
  
      mapping(bytes32 => Record) private docHashes;
  
      constructor() { }
  
      function addDocHash(bytes32 hash) public {
          Record memory newRecord = Record(block.timestamp, block.number);
          docHashes[hash] = newRecord;
      }
  
      function findDocHash(bytes32 hash) public view returns (uint, uint) {
          return (docHashes[hash].mineTime, docHashes[hash].blockNumber);
      }
  }

• Compile the code : truffle compile

• Create a migration file : truffle create migration Diploma

• Edit the generated JavaScript file xxx_diploma.js to tells Truffle to obtain a reference to the Diploma contract and deploy it :

  var DiplomaContract = artifacts.require("Diploma");
  module.exports = function(deployer) {
      deployer.deploy(DiplomaContract);
  };

• Start Ganache, create a workspace and link the Truffle project by selecting the truffle-config.js file

• Edit the truffle-config.js file which is the main configuration file, to configure the network to connect to the development blockchain (provided by Ganache) :

  development: {
      host: "localhost",
      port: 7545,
      network_id: "*"
  }

• Deploy the contract onto the test blockchain : truffle migrate --network development

• To redeploy, simply add the --reset option : truffle migrate --network development --reset

• Connect to truffle console (uses the web3js library) : truffle console

• We can now interact with the contract using javascript console (I have first generated a SHA256 hash from a file) :

  Diploma.address
  diploma = await Diploma.deployed();
  diploma.addDocHash("0x816bf8b135fb51711d0622a2ae156b6b4505d9ba83ae243ff1fb26d8300d9bdf");
  diploma.findDocHash("0x816bf8b135fb51711d0622a2ae156b6b4505d9ba83ae243ff1fb26d8300d9bdf");

• Write tests (it uses Mocha/Chai) by creating a diploma.js file under the test directory :

  const Diploma = artifacts.require("Diploma");
  contract("Diploma test", async accounts => {
    it("check that the balance increase", async () => {
      // test here
    });
  });

• run tests : truffle test ./test/diploma.js

You can at any moment explore the blockchain via Ganache UI :

Java

To interact with the blockchain via Java :

• Add Java Ethereum Web3j dependency :

  <dependency>
    <groupId>org.web3j</groupId>
    <artifactId>core</artifactId>
    <version>5.0.0</version>
  </dependency>

• Either :
  • interact with the deployed contract using raw methods
  • use Web3j command line tools or Web3j Maven plugin (requires solc compiler) to generate a contract wrapper (Java class) that can be used to interact with the contract

See eth-hash-app project for more details.

Installation

1. Clone the repository :

   git clone https://github.com/Yann39/eth-hash-chain

2. Navigate to the contracts directory from your CLI
3. Compile the smart contract using Truffle :

   truffle compile

4. Deploy the contract onto the test blockchain :

   truffle create migration Diploma

License

General Public License (GPL) v3

This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program. If not, see http://www.gnu.org/licenses/.