An introduction to newbies. What is a blockchain and why to use it? Ethereum technology vs Bitcoin technology. Smart contracts. Solidity programming. An example smart contract.

1. BLOCKCHAIN, ETHEREUM,
SMART CONTRACTS,
TOKENS
Dr. Yoram Kornatzky
kornatzky@gmail.co
m
http://yoramkornatzky.com

2. Bank
The Banking System
Accounts
Ledger
Transaction
Consumer: Joe
Contractor: Julia

3. Money Transfer
Paris Bank Frankfurt Bank
Swift
Sophie Johannes
Transaction Transaction

4. BLOCKCHAIN
• A decentralised ledger - distributed across many
computers
• No central server - bank
• Collection of computers - peers
• Each holding the ledger
• Consensus among computers
• P2P

5. The Network - P2P

6. Blockchain
1003
4
2 1 0…
Tx1
Tx4
Tx2
Tx3

7. THE INCENTIVE
• Payment
• Ether / Bitcoin
• Accounts

8. ETHEREUM
• Blockchain
• Each node runs an Ethereum Virtual
Machine (EVM)
• Solidity Programming Language
• Turing Complete

9. GETH -
ETHEREUM GO CLIENT
brew install geth
# get the file genesis.json
geth - - datadir=~/datadir init genesis.json
geth - - datadir=~/datadir account new
# will request password

11. GETH - JAVASCRIPT
CONSOLE
geth - - datadir=~/datadir

12. > eth.accounts
["0xb91b6b1840ed6850ddedc67564b2049f51e53baa",
“0x13114f57a2240c4d870d95a8ab1ad3c0dacca26a"]
> eth.getBalance("abcxyz")
Error: invalid address
at web3.js:3930:15
at web3.js:5025:28
at map (<native code>)
at web3.js:5024:12
at web3.js:5050:18
at web3.js:5075:23
at <anonymous>:1:1
> eth.getBalance("0xb91b6b1840ed6850ddedc67564b2049f51e53baa")
2.4179e+22

13. > web3.fromWei(eth.getBalance(eth.accounts[0]), "ether")
24179
> eth.sendTransaction({from: eth.accounts[0], to:
eth.accounts[1], value: web3.toWei(3, "ether")})
Error: authentication needed: password or unlock
at web3.js:3143:20
at web3.js:6347:15
at web3.js:5081:36
at <anonymous>:1:1
> personal.unlockAccount(eth.accounts[0], "secret")
true

14. > eth.sendTransaction({from: eth.accounts[0], to:
eth.accounts[1], value: web3.toWei(3, "ether")})
INFO [01-27|13:58:06] Submitted transaction
fullhash=0x6c6226f6bf411cc9a1ccc2071127482d6b62eb1b300e
83209f72d5bfa105c536
recipient=0x13114F57a2240C4D870d95A8AB1ad3C0daCCa26
A
“0x6c6226f6bf411cc9a1ccc2071127482d6b62eb1b300e83209f7
2d5bfa105c536"

16. SMART CONTRACT
• Executed on all nodes
• Costs Ether - gas
• Solidity programming language

17. MINIMAL TOKEN
CONTRACT
pragma solidity ^0.4.0;
contract MinimalToken {
mapping (address => uint256) public
balanceOf;
}

18. function MinimalToken(uint256 initialSupply) public {
balanceOf[msg.sender] = initialSupply;
}
function transfer(address _to, uint256 _value) public{
require(balanceOf[msg.sender] >= _value);
require(balanceOf[_to] + _value >= balanceOf[_to]);
balanceOf[msg.sender] -= _value;
balanceOf[_to] += _value;
}