Agenda Blockchain – Key points Ethereum – Introduction DApp – Environment development DApp – General architecture DApp – Demo building auction application

1. How to develop Decentralized
Apps on Ethereum
Thien Nguyen

2. About me
• Native name: Nguyễn Lê Quỳnh Thiện
• From: Vietnam
• Engineering Manager at NashTech
• Founder of SimplCommerce
• Microsoft MVP
• @thiennlq

3. Agenda
• Blockchain – Key points
• Ethereum – Introduction
• DApp – Environment development
• DApp – General architecture
• DApp – Demo building auction application

4. Bitcoin History
• “Bitcoin: A Peer-to-Peer Electronic Cash System” Nov, 2008 by Satoshi
Nakamoto https://bitcoin.org/bitcoin.pdf
• First implementation released in Jan 2009 by Satoshi Nakamoto

5. How bitcoin works
DB

6. Digital Signature

7. Hash Function
• Arbitrary input
• Same length output
• Unlikely that two inputs share
the same output

8. Merkle Trees (Hashes of hashes)
https://www.youtube.com/watch?v=-SMliFtoPn8

9. Blocks

10. Proof of Work
https://www.youtube.com/watch?v=bBC-nXj3Ng4

11. Blockchains
• Distributed (Everybody keep their own copy of the ledger)
• Transaction immutability achieved by way of blocks & chaining
• Leverages consensus mechanism for validating the transactions
• Uses cryptography for trust, accountability, security
• There is no single point of failure

12. Blockchain – Innovation Journey

14. https://www.youtube.com/watch?v=-SMliFtoPn8

15. Ethereum Accounts
• Has an address
• Controlled by a private key
• Has an address
• No private key
• Holds and run code
External Owned Account
Contract Account

16. Go Etherum Client
Geth
ÐΞVp2p [TCP, 30303]
> JS API Console
IPC-RPC
WS-RPC [8546]
JSON-RPC [HTTP, 8545]
Disabled by default
Disabled by default

17. Ethereum Networks
• Network Id = 1
• Morden: Network Id = 2 (retired)
• Ropsten: Network Id = 3
• Rinkerby: Network Id = 4
• Kovan: Network Id = 42
• Network Id = Assigned
Live Network
Testnet
Private Network

18. DEMO
Setup a private Ethereum network
https://github.com/devcafevn/ethereum-auction-app/tree/master/private-network

19. Using Ethereum Wallet and MetaMask
Ethereum Wallet MetaMask
You can install the MetaMask add-on in Chrome, Firefox,
Opera
https://github.com/ethereum/mist/releases

20. Denominations
Unit Wei Value Wei
wei 1 wei 1
Kwei (babbage) 1e3 wei 1,000
Mwei (lovelace) 1e6 wei 1,000,000
Gwei (shannon) 1e9 wei 1,000,000,000
microether (szabo) 1e12 wei 1,000,000,000,000
milliether (finney) 1e15 wei 1,000,000,000,000,000
ether 1e18 wei 1,000,000,000,000,000,000

21. GAS
• Gas is the unit in which EVM resource usage is measured
• Gas limit (start gas): max amount of gas you willing to spend
• Gas price: price of gas on ether you willing to pay. Miners decides the
minimal acceptable price
Transaction Fee = Gas used * Gas price
Gas used < Gas limit
=> Refund
Gas used > Gas limit
=> Out of gas exception, no change made

22. Remix - https://remix.ethereum.org
• Writing your first smart contract
pragma solidity ^0.4.0;
contract MyAccount {
uint private myBalance;
function MyAccount(uint _myBalance) public{
myBalance = _myBalance;
}
function getBalance() public constant returns(uint){
return myBalance;
}
function add(uint _amount) public returns(uint){
myBalance += _amount;
return myBalance;
}
}

23. DApp - General Architecture
Network
JSON-RPC / WS-RPC

24. DApp - General Architecture 2
Network
DB
Server
REST API

25. Demo
Online Auction Application

26. Online Auction App
• Everyone can send their bids to a
contract
• The highest current bid is visible
to every one
• At the end of the bidding period
• The highest bid is sent to the
beneficiary
• Other bidders can withdraw their
bids
Image source: https://kryptomoney.com/italian-auction-house-now-accepting-payments-
bitcoins/
Source code: https://github.com/devcafevn/ethereum-auction-app

27. References
• https://bitcoin.org/bitcoin.pdf
• https://www.ethereum.org/
• http://www.ethdocs.org/en/latest/
• https://solidity.readthedocs.io/en/v0.4.25/
• https://www.youtube.com/watch?v=bBC-nXj3Ng4
• https://www.youtube.com/watch?v=-SMliFtoPn8
• https://github.com/devcafevn/ethereum-auction-app

28. Thank you!