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Building Decentralized Apps (DApps) in Ethereum

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In the session the speaker explains the concepts of smart contracts and DApps and demonstrates how to build, deploy and run a simple decentralized app in the Ethereum blockchain network, using a Solidity smart contract, with a JavaScript-based front-end, interacting with the contract through the MetaMask in-browser wallet and the Ethereum Web3 API.

The DApp is called “Document Registry” and is simple: it holds a set of documents and can confirm the existence of certain document (e.g. course certificate, diploma of graduation or loan contract) at certain date in the past. The DApp uses the decentralized storage system IPFS to hold the document contents and keeps their hashes on the blockchain (in the Ropsten Testnet for the demo).

Demo: https://document-registry-nakov.herokuapp.com

Source code: https://github.com/nakov/Ethereum-Web3-Document-Registry-Demo

Blog post: https://nakov.com/blog/2018/10/11/svetlin-nakov-speaker-blockchain-economy-istanbul-summit-2019/

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Building Decentralized Apps (DApps) in Ethereum

  1. 1. Using Solidity, MetaMask, JS and Web3 to Build DApp on the Ropsten Testnet Building Decentralized Apps (DApps) in Ethereum Dr. Svetlin Nakov Co-Founder, Chief Training & Innovation @ Software University (SoftUni) http://nakov.com Software University (SoftUni) – http://softuni.org
  2. 2.  Software engineer, trainer, entrepreneur, PhD, author of 15 books, blockchain expert  3 successful tech educational initiatives (150,000+ students) About Dr. Svetlin Nakov 2
  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:  Aeternity Ventures, Tokenize Exchange, Bountie, Weidex, IRIS Payments Solutions, FFQuest, Blockchain List, Bullcandle Nakov – Blockchain & Crypto Projects 3
  4. 4. DApps – Introduction
  5. 5. Decentralized Systems 5 Peer-to-Peer Network (p2p) Decentralized (no owner, no central point of control) Consensus (all nodes hold the same state)
  6. 6. Blockchain == Chain of Data Blocks 6 timestamp block_hash all_transactions_hash transaction #1 hash transaction #2 hash transaction #3 hash … Block #0 (genesis block) prev_hash nonce timestamp block_hash all_transactions_hash transaction #1 hash transaction #2 hash transaction #3 hash … Block #1 prev_hash nonce timestamp block_hash all_transactions_hash transaction #1 hash transaction #2 hash transaction #3 hash … Block #2 prev_hash nonce Blockchain == p2p network, holding a synchronized chain of blocks (ledger)
  7. 7. Blockchain Applications 7 Digital money with no central bank Cryptocurrencies Decentralized Applications Removing the middlemen Digital Investments and Trading ICO / STO / token economies
  8. 8. Smart Contracts 8 Code (program logic) running on the blockchain Smart Contracts Programming language for the Ethereum EVM Solidity
  9. 9.  Smart contract blockchain networks  Ethereum – ethereum.org  EOSIO – eos.io  NEO, NEM, Cardano, Hyperledger  Decentralized storage systems  IPFS – ipfs.io  Decentralized databases  BigChainDB – bigchaindb.com DApp Platforms and Technologies 9
  10. 10. Document Registry DApp
  11. 11. Ethereum Wallets and MetaMask 11 Securely hold private keys, controlling crypto assets Blockchain Wallets Ethereum wallet integrated in the browser MetaMask
  12. 12.  Admins submit documents  E.g. diplomas / certificates  Hashes are stored on chain  Users verify documents  Valid / invalid  Technologies: Ethereum Ropsten Testnet, Solidity, MetaMask, JavaScript, Web3 Document Registry DApp 12 https://document-registry-nakov.herokuapp.com
  13. 13. The DApp Code in GitHub 13https://github.com/nakov/Ethereum-Web3-Document-Registry-Demo
  14. 14. Remix IDE for Solidity 14 https://remix.ethereum.org
  15. 15. The Smart Contract (in Solidity) 15
  16. 16. Transactions on the Ropsten Testnet 16
  17. 17. Submitting a Document 17
  18. 18. Submitting a Document: MetaMask 18
  19. 19. The Document is Published on the Chain 19
  20. 20. Wait for the Transaction to be Mined 20
  21. 21. Verify a Document: Smart Contract Read 21
  22. 22. Verify a Document: Smart Contract Read 22
  23. 23. https://nakov.com Building DApps in Ethereum

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