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Where’s my money scenario \w friend

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Where’s my money scenario \w friend

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Where’s my money scenario \w friend

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Where’s my money scenario \w friend

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Where’s my money scenario \w friend

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Where’s my money scenario \w friend

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KTB & people shouting “Where’s my money”

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A Ledger

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TODO: Neighborhood picture

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A Centralized Approach

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TODO: Centralized Problems

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TODO: Centralized Problems

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public class Transaction { private String sender; private String recipient; private int amount; // constructor, getters, setters, toString... }

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public class Block { private final List transactions; // constructor, getters, setters, toString... }

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public class Blockchain { private List blocks; // constructor, getters, setters, toString... }

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public class Blockchain { private List blocks; private List pendingTransactions; // constructor, getters, setters, toString... }

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// … // TODO: Implement Peer Synchronization // …

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Fake Transactions

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TODO: Rebecca buying a bike from Peter

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// … // TODO: Implement Signatures // …

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Making the Ledger Immutable

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public class Block { private final List transactions; private final String prevBlockHash; private final String blockHash; // constructor, getters, setters, toString... }

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Achieving Consensus

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public class Block { private final List transactions; private final long nonce; private final String prevBlockHash; private final String blockHash; // constructor, getters, setters, toString... }

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public BlockCandidate getMiningJob() { String lastBlockHash = blocks.get(blocks.size() - 1) .getBlockHash(); return new BlockCandidate( pendingTransactions, lastBlockHash); }

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public void submitBlock(Block newBlock) { if (isValidBlock(newBlock)) { blocks.add(newBlock); } else { throw new IllegalArgumentException("Invalid block"); } }

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private boolean isValidBlock(Block block) { // … // intermediary calculations… // … return prevBlockHash.equals(lastBlock.getBlockHash()) && calculatedBlockHash.equals(blockHash) && Utils.startsWithZeroes(blockHash, difficulty); }

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public void mine(Blockchain blockchain) { // intermediary calculations… while (!startsWithZeroes(blockHash, difficulty)) { nonce++; String blockData = prevBlockHash + transactions + nonce; blockHash = Utils.calculateSHA256(blockData); } // submit mined block… }

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Longest Chain Consensus

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51% Attack

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public class Blockchain { private List blocks; private List pendingTransactions; private int difficulty = 4; // constructors, getters, setters, toString… }

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TODO: Mining Rewards

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// … // TODO: Implement Mining Rewards // …

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• Live Demo

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• Link to app in github

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Act 3: Blockchain’s Evolution

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Data -> Code

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Data -> Code

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Data -> Code

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Data -> Code

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Data -> Code

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Smart Contracts

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In Sum…

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Data -> Code

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It all sounds great but…

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Blockchain is still a baby

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Blockchain the next big thing & people laughing

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The Earth is round & people laughing

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Now is the time for pioneers

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Now is the time for pioneers