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Client-Side Wallets in DApps - Nakov @ BlockWorld 2018 (San Jose)

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Client-Side Wallets in DApps - Svetlin Nakov @ BlockWorld 2018 (San Jose, CA, USA)

In this talk Svetlin Nakov explains a few architectures for handling the wallets and keys in DApps: server side wallet, client-side wallet and MetaMask.

Nakov demonstrates how to build a client-side BIP39 / BIP44 wallet (using the Ethers.js library) and keep the encrypted JSON wallet at the servers side, along with the username / password credentials.

During the user registration a wallet JSON is generated and sent to the server. After login the wallet JSON is downloaded from the server. Users should enter a password to decrypt the JSON wallet when they sign transactions.

Learn more at: https://github.com/nakov/client-side-ethereum-wallet

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Client-Side Wallets in DApps - Nakov @ BlockWorld 2018 (San Jose)

  1. 1. Client-Side Wallets in DApps DApps: Architectures and Wallet Interaction, Client-Side and Server-Side Interaction with the Blockchain Software University (SoftUni) https://softuni.org Svetlin Nakov Blockchain Engineer and Technical Trainer
  2. 2. 2  Software engineer, trainer, entrepreneur, PhD, author of 12 books, blockchain expert  3 successful tech educational initiatives (100,000+ students): About Svetlin Nakov
  3. 3. 3  Technical advisor @ LockChain / LockTrip: https://locktrip.com  Raised ~ 10.000 ETH in token sale (Sep-Nov 2017)  Currently LOC token holders book hotels @ 20-30% better price  Head of blockchain education (Jan-June 2018) @ Academy School of Blockchain: https://academytoken.com  Raised ~ 48M USD in token sale (Jan-Apr 2018)  Tech advisor for blockchain crypto startups:  Tokenize Exchange, Bountie, Weidex, IRIS Payments Solutions, Aeternity Ventures Nakov – Blockchain & Crypto Projects
  4. 4. Table of Contents 4 1. Decentralized Blockchain Apps (DApps) Architectures 2. Server-Side Interaction with the Blockchain 3. Client-Side Interaction through MetaMask 4. Client-Side JS Wallet (using Ethers.js) 5. Live Demo: Voting DApp with Client-Side JS Wallet 6. Security Notes and Possible Attacks
  5. 5. 5 Decentralized Blockchain Apps (DApps) DApps Hold code + data on the blockchain / p2p network The front-end is still a traditional app Client App (front-end) Smart Contract Backend Code + data on the blockchain Traditional Backend Server-side code + data HTTP JSON RPC JSON RPC
  6. 6. 6  Note: the server-side wallet signs all transactions  it might be subject to hard hacker attacks  don't keep large amounts in it! Server-Side Interaction with the Blockchain Client App (front-end) Backend App (JS / Java / C# / Python / PHP / Ruby / Go / …) RPC Server Wallet Local geth / Parity node Or remote RPC, e.g. api.infura.io HTTP
  7. 7. 7  Document Registry DApp  Goal: keep a set of authentic documents on the blockchain  Users can view / verify documents, published on the blockchain  PDF documents hosted in decentralized storage (like IPFS)  Document hashes published in a smart contract  Admins can upload new documents  Blockchain transactions are signed at the server-side  Encrypted server-side wallet, unlocked by admin's password Sample Scenario for Server-Side Interaction
  8. 8. Client App (front-end) JS Wallet 8 Client-Side Interaction through MetaMask  Use MetaMask to protect private keys and sign transactions client-side  MetaMask is currently unavailable on mobile devices! geth / Parity node at the server-side Or remote RPC, e.g. api.infura.io HTTP Backend App (JS / Java / C# / Python / PHP / Ruby / Go / …) RPC
  9. 9. 9  The "CryptoKitties" Game  Goal: view, purchase, breed and sell collectable items (kitties)  https://www.cryptokitties.co  Site visitors can browse the kitties, published on the blockchain  Server-side logic reads the kitties from the blockchain  Registered users can purchase / sell kitties  MetaMask is used to sign transactions / interact with smart contracts  MetaMask addon provides "Injected Web3 API" inside the browser Sample Scenario for MetaMask Interaction
  10. 10. 10  Using a client-side JS wallet (e.g. Ethers.js / LightWallet) simplifies the interaction and delegates the security risks to the end-users Client-Side Interaction with the Blockchain geth / Parity node at the server-side Or remote RPC, e.g. api.infura.io RPCHTTP Client App (front-end) JS Wallet Backend App (JS / Java / C# / Python / PHP / Ruby / Go / …)
  11. 11. 11  User registers in a mobile app / Web app  A client-side wallet is created during the registration  The wallet JSON is stored in the app / browser's LocalStorage  Strong encryption (AES + Scrypt / Argon2), based on strong password  Optionally the wallet JSON can be stored at the server-side or in Dropbox / Storj / IPFS (readable by password-derived key)  Security assumptions:  The username, password & private key never leave the client app!  All transactions are signed client-side, never at the server-side! Client-Side JS Wallet
  12. 12. 12  Voting App  Users register and get a new random wallet (private key + address)  The wallet JSON is stored at the server-side, after strong encryption  The wallet password / private key never leave the client app  User login  download the encrypted wallet JSON from the server  After login / register, keep the encrypted wallet JSON in the browser session  Logout  clear the browser session  Use different passwords for server login and for the wallet (HMAC-derived)  Lost password == lost wallet  no "reset password", use the mnemonics Sample Scenario for Client-Side JS Wallet
  13. 13. Live Demo: Voting DApp with Client-Side JS Wallet Source: https://github.com/nakov/client-side-ethereum-wallet Demo: https://client-side-wallet-demo.herokuapp.com
  14. 14. 14  The wallet server keeps: [WalletID  encrypted wallet (JSON)]  WalletID = HMAC(username, password + 'server')  Wallet password = HMAC(password, username + 'wallet')  Client-side attacks  Hacked laptop  stolen private key (it is decrypted to vote)  Server-side attacks  Hacked server  stolen JSON files  long password (derived from username + pass) + unknown username  decrypting infeasible  Still, hackers may inject malicious JS code in the client-side app Security and Possible Attacks
  15. 15. ? Client-Side Wallets in DApps https://softuni.org
  16. 16. License  This course (slides, examples, demos, videos, homework, etc.) is licensed under the "Creative Commons Attribution- NonCommercial-ShareAlike 4.0 International" license 16
  17. 17. Trainings @ Software University (SoftUni)  Software University – High-Quality Education, Profession and Job for Software Developers  softuni.org  Software University Foundation  softuni.foundation  Software University @ Facebook  facebook.com/SoftwareUniversity  Software University Forums  forum.softuni.bg

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