Android Document Sharing System using Blockchain Technology

This guide demonstrates how to build an Android Document Sharing System utilizing Blockchain Technology. This system leverages blockchain’s decentralized and immutable characteristics to enhance the security and integrity of document sharing on Android devices.

System Overview

The Android Document Sharing System on Blockchain includes:

• Decentralized Document Storage: Store document metadata and hashes on the blockchain to ensure tamper-proof records.
• Document Integrity: Use blockchain to verify the integrity of shared documents and prevent unauthorized alterations.
• Secure Sharing: Implement access controls and encryption to secure document sharing among users.
• Efficient Retrieval: Enable users to retrieve and verify documents using blockchain data.

System Design

Follow these steps to design and implement the system:

1. Choose a Blockchain Platform

   Select a blockchain platform suitable for document management and smart contracts. Ethereum and Hyperledger Fabric are popular choices for such use cases.

2. Set Up Development Environment

   Prepare your development environment with the necessary tools and libraries for blockchain and Android development. Install Truffle for smart contract development and Android Studio for app development.

   
                           npm install -g truffle
                           npm install web3
                       

3. Develop Smart Contracts

   Create smart contracts for managing document metadata, access control, and document verification. Below is an example smart contract:

   
                           pragma solidity ^0.8.0;
   
                           contract DocumentSharing {
                               address public owner;
   
                               struct Document {
                                   string docHash;
                                   string docName;
                                   address[] allowedUsers;
                                   bool isShared;
                               }
   
                               mapping(string => Document) public documents;
   
                               event DocumentUploaded(string indexed docHash, string docName, address indexed uploader);
                               event DocumentShared(string indexed docHash, address indexed user);
   
                               constructor() {
                                   owner = msg.sender;
                               }
   
                               modifier onlyOwner() {
                                   require(msg.sender == owner, "Not authorized");
                                   _;
                               }
   
                               function uploadDocument(string memory _docName, string memory _docHash) public onlyOwner {
                                   documents, false);
                                   emit DocumentUploaded(_docHash, _docName, msg.sender);
                               }
   
                               function shareDocument(string memory _docHash, address _user) public onlyOwner {
                                   Document storage doc = documents[_docHash];
                                   require(bytes(doc.docName).length > 0, "Document does not exist");
                                   doc.allowedUsers.push(_user);
                                   doc.isShared = true;
                                   emit DocumentShared(_docHash, _user);
                               }
   
                               function getDocument(string memory _docHash) public view returns (string memory, address[] memory, bool) {
                                   Document memory doc = documents[_docHash];
                                   return (doc.docName, doc.allowedUsers, doc.isShared);
                               }
                           }
                       

4. Develop the Backend

   Build a backend to interact with the smart contracts and handle document metadata. Example code for interacting with the smart contract:

   
                           const Web3 = require('web3');
                           const web3 = new Web3('https://mainnet.infura.io/v3/YOUR_INFURA_PROJECT_ID');
                           const contractABI = [...] // Replace with your contract ABI
                           const contractAddress = '0xYourContractAddress';
                           const contract = new web3.eth.Contract(contractABI, contractAddress);
   
                           async function uploadDocument(docName, docHash) {
                               const accounts = await web3.eth.getAccounts();
                               await contract.methods.uploadDocument(docName, docHash)
                                   .send({ from: accounts[0] });
                           }
   
                           async function shareDocument(docHash, userAddress) {
                               const accounts = await web3.eth.getAccounts();
                               await contract.methods.shareDocument(docHash, userAddress)
                                   .send({ from: accounts[0] });
                           }
   
                           async function getDocument(docHash) {
                               return await contract.methods.getDocument(docHash).call();
                           }
                       

5. Implement Document Encryption

   Encrypt documents before uploading them to ensure data security. Use asymmetric encryption algorithms for encrypting and decrypting documents.

6. Develop the Android App

   Create an Android app with functionalities for uploading documents, sharing documents, and retrieving documents using blockchain data. Use libraries such as Web3j for Ethereum integration in Android.

   
                           // Example code for interacting with the smart contract in Android
                           Web3j web3j = Web3j.build(new HttpService("https://mainnet.infura.io/v3/YOUR_INFURA_PROJECT_ID"));
                           Credentials credentials = WalletUtils.loadCredentials("password", "path/to/wallet/file");
                           DocumentSharing contract = DocumentSharing.load(CONTRACT_ADDRESS, web3j, credentials, new DefaultGasProvider());
   
                           // Upload document
                           contract.uploadDocument("DocumentName", "DocumentHash").send();
   
                           // Share document
                           contract.shareDocument("DocumentHash", "UserAddress").send();
                       

7. Testing and Deployment

   Thoroughly test the system to ensure it functions as intended:

   • Functional Testing: Verify document upload, sharing, and retrieval functionalities.
   • Security Testing: Assess the security of document encryption and blockchain interactions.
   • Deployment: Deploy the smart contracts to the blockchain, set up the backend, and publish the Android app.