![29
THIS IS AN EXAMPLE SMART
CONTRACT WRITTEN IN SOLIDITY
contract MyToken {
/* This creates an array with all balances */
mapping (address => uint256) public balanceOf;
/* Initializes contract with initial supply tokens to the creator of the contract */
function MyToken(
uint256 initialSupply
) {
balanceOf[msg.sender] = initialSupply; // Give the creator all initial tokens
}
/* Send coins */
function transfer(address _to, uint256 _value) {
if (balanceOf[msg.sender] < _value) throw; // Check if the sender has enough
if (balanceOf[_to] + _value < balanceOf[_to]) throw; // Check for overflows
balanceOf[msg.sender] -= _value; // Subtract from the sender
balanceOf[_to] += _value; // Add the same to the recipient
}
}](https://image.slidesharecdn.com/introductiontoblockchain-170408105544/85/Grokking-TechTalk-17-Introduction-to-blockchain-29-320.jpg)
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Grokking TechTalk #17: Introduction to blockchain
- 2. 2 Agenda 1. What is a Blockchain? 2. Introduction to Ethereum
- 3. 3 1. WHAT IS A BLOCKCHAIN?
- 4. 4 FIRST, WHY DO WE CARE ABOUT BLOCKCHAINS? A blockchain allows for trustless transactions between multiple parties. Or, more importantly, it allows transactions without trust of a third party intermediary!
- 5. 5 BLOCKCHAIN = DISTRIBUTED LEDGER + CONSENSUS
- 6. 6 BLOCKCHAIN = DISTRIBUTED LEDGER + CONSENSUS A list of transactions between accounts (a ledger) are stored on distributed “nodes”. New transactions are periodically added into a block. Nodes use an agreed upon protocol to reach consensus on when a new block is appended to the chain of previous blocks.
- 7. 7 A TRANSACTION THAT OCCURS BETWEEN ACCOUNTS Transaction #399 Account A Account B E.g. Send 10 tokens An example transaction could be: Account A will send 10 tokens to Account B
- 8. 8 A LEDGER IS A LIST OF TRANSACTIONS (GROUPED INTO BLOCKS) LEDGER Block #100 Last Block: #99 Transaction #399 Transaction #400 Transaction #401 Block #97 Block #98 Block #99
- 9. 9 BLOCKS ARE CHAINED TOGETHER LEDGER Block #100 Last Block: #99 Transaction #399 Transaction #400 Block #97 Block #98 Block #99 The ledger is a chain of blocks! Each block is created with a pointer to the previous block creating a blockchain! The ledger is a chain of blocks! Each block is created with a pointer to the previous block creating a blockchain!
- 10. 10 THE LEDGER IS COPIED AND DISTRIBUTED AMONG NODES � � � � �
- 11. 11 EACH NODE HAS A COPY OF THE LEDGER AND AT LEAST ONE OF THEM WILL CREATE THE NEXT BLOCK! � � � � � 11
- 12. 12 EXAMPLE CONSENSUS PROTOCOL: PROOF OF WORK Different methods or protocols exist for distributed nodes to reach consensus
- 13. 13 NODES ATTEMPTING TO CREATE NEW BLOCKS ARE USUALLY CALLED “MINERS” � � � � �The first Miner to solve a hard math problem creates the next block and is rewarded
- 14. 14 E.g. Bitcoin Miners currently receive 12.5 BTC plus all included transaction fees New block: Every ~10 minutes THE MAJORITY OF PoW BLOCKCHAINS INCENTIVIZE MINERS WITH REWARDS E.g. Ethereum Miners currently receive 5 ETH plus all included gas fees (more on this shortly) New block: Every ~15 seconds
- 15. 15 A BRIEF HISTORY OF BLOCKCHAINS ▸ 2008: Bitcoin and blockchain idea gifted to world by “Satoshi Nakamoto” ▸ 2009: Bitcoin client released (open source) ▸ 2011: Litecoin, first “altcoin,” released (based on bitcoin source code) ▸ 2014: Ethereum whitepaper released/crowdsale ▸ 2015: Ethereum “Frontier” launched
- 17. 17 WHAT IS ETHEREUM? OPEN SOURCE Like Bitcoin, Ethereum is a public blockchain no one controls or owns.
- 18. 18 WHAT IS ETHEREUM? OPEN SOURCE Like Bitcoin, Ethereum is a public blockchain no one controls or owns. PROOF OF WORK CONSENSUS The Ethereum Whitepaper specifies the PoW rules and 4+ major clients exist and run the “nodes”.
- 19. 19 WHAT IS ETHEREUM? OPEN SOURCE Like Bitcoin, Ethereum is a public blockchain no one controls or owns. PROOF OF WORK CONSENSUS The Ethereum Whitepaper specifies the PoW rules and 4+ major clients exist and run the “nodes”. ETHEREUM VIRTUAL MACHINE (EVM) Transactions are more than just values, but “Turing” complete programs that run when blocks are processed by nodes.
- 20. 20 ETHEREUM VIRTUAL MACHINE General Purpose Supports Bitcoin- like value transactions (e.g. send 10 ETH from account A to B) or more complex applications.
- 21. 21 ETHEREUM VIRTUAL MACHINE General Purpose Supports Bitcoin- like value transactions (e.g. send 10 ETH from account A to B) or more complex applications. Smart Contracts Turing complete languages (e.g. Solidity) allow the Ethereum transactions to be programmed to do different operations.
- 22. 22 ETHEREUM VIRTUAL MACHINE General Purpose Supports Bitcoin- like value transactions (e.g. send 10 ETH from account A to B) or more complex applications. Smart Contracts Turing complete languages (e.g. Solidity) allow the Ethereum transactions to be programmed to do different operations. Decentralized Apps (DApps) GUIs for smart contracts allow users to interact in ways similar to web 2.0 (HTML/JS/CSS).
- 23. 23 THINK: WORLD COMPUTER The Ethereum blockchain is the first “decentralized world computer” to ever exist!
- 24. 24 TRANSACTIONS AND CONTRACTS Two types of Accounts ▸ Externally owned accounts (controlled by people/keys similar to Bitcoin) ▸ Contract accounts (controlled by smart contract code)
- 25. 25 TRANSACTIONS AND CONTRACTS Transactions can include more than just value transfer; they can include programming or bytecode that does things (smart contracts) Transaction #3512 If (Account A == Member) && (Date >= 4Q): Dividend = 25% the current value of Contract C: Transaction: Contract C Account A Send Dividend
- 26. 26 TRANSACTIONS AND CONTRACTS Submitting transactions and contracts to the blockchain has an associated “gas” cost paid in Ether based on the complexity of the operations. Transaction #256 If (Account A == Member) && (Date >= 4Q): Dividend = 50% the current value of Contract C: Transaction: Contract C Send Dividend IF +70 Gas AND +30 Gas EQUAL? +40 Gas DIVIDE +120 Gas SEND +20 Gas TOTAL COST = 280 Gas
- 27. 27 TRANSACTIONS AND CONTRACTS LEDGER Block #26 Last Block: #25 Transaction #256 Transaction #257 Transaction #258 Block #23 Block #24 Block #25
- 28. 28 TRANSACTIONS AND CONTRACTS Think of the Ethereum Ledger like a SPREADSHEET Cells can just have a value or they can give the result of a macro/script. Trans- action Account A Account B Account C (Contract) #256 10 10 0 #257 5 5 10 #258 10 5 Dividend(A)
- 29. 29 THIS IS AN EXAMPLE SMART CONTRACT WRITTEN IN SOLIDITY contract MyToken { /* This creates an array with all balances */ mapping (address => uint256) public balanceOf; /* Initializes contract with initial supply tokens to the creator of the contract */ function MyToken( uint256 initialSupply ) { balanceOf[msg.sender] = initialSupply; // Give the creator all initial tokens } /* Send coins */ function transfer(address _to, uint256 _value) { if (balanceOf[msg.sender] < _value) throw; // Check if the sender has enough if (balanceOf[_to] + _value < balanceOf[_to]) throw; // Check for overflows balanceOf[msg.sender] -= _value; // Subtract from the sender balanceOf[_to] += _value; // Add the same to the recipient } }
- 30. 30 USE CASES FOR DAPPS AND PROJECTS IN DEVELOPMENT Decentralized Exchange Convert between crypto-currencies and tokens EtherDelta, EtherEx Prediction Market Utilize the wisdom of the crowd to predict future events Augur, Gnosis Distributed Computing Enable users to lease out spare compute cycles (think: uber for your computer, dAWS) Golem Identity Management Retain ownership of your online identity, metadata, and relationships. uPort Crowd Sale Platform Create a custom token for trade, payment, customer loyalty, etc. and take it to market. Ethereum, Firstblood Digital Asset Management Manage, buy, sell physical objects cryptographically tied to digital tokens. Digix
- 31. 31 Thank you for your listening