Introduction to Blockchain Technology

Transcription

1 Introduction to Blockchain Technology Current Trends in Artificial Intelligence Volker Strobel PhD IRIDIA 23 February 2017

2 Part I: Bitcoin: Idea, Basics, Technology Part II: Altcoins, Use cases, Blockchain applications 2

3 Part I: Bitcoin: Idea, Basics, Technology Part II: Altcoins, Blockchain applications, Use cases 3

4 Bitcoin is a digital currency without the need of banks and governments Government Bank Alice transaction 4 Bob Peer 1 Peer 2

5 Why would you want to remove the bank? save costs transaction speed don t trust the bank be anonymous be able to pay ideological reasons censorship non-reversible transactions micropayments payments triggered by events flexibility 5

6 Developing a peer-to-peer financial system poses many challenges: How to validate transactions? How to create new money? How to trust the system? How to prevent double-spending? How to reach consensus on who owns what?? 6

7 7

8 Understand the Blockchain in Two Minutes by the Institute for the Future (IFTF) ( 8

9 Every participant keeps his/her own copy of the ledger Peer-to-peer network 9

10 To transfer Bitcoin tokens, participants publicly announce transactions Transaction: Send 3 Bitcoins from Alice to Bob Is this transaction really from Alice? 10

11 Digital Signatures Public-key cryptography document private/secret key (sk) signature public key (pk) sign( document, sk) = signature verify( document, pk, signature) = bool 11

12 A quick example of digital signatures Distribute public key: gpg --armor --output volker.gpg export Import public key (on another machine): gpg --import volker.gpg Create message: echo "hello blockchain" > msg.txt Sign message: gpg --clearsign -o sig.gpg msg.txt Send sig.gpg via Verify message (on another machine): gpg --verify sig.gpg 12

13 How to ensure that everyone has the same version of? Peer-to-peer network Majority consensus? => Sybil attacks 13

14 You trust the ledger with the highest amount of computational work (often called the longest chain but it s rather the strongest chain) work: 2 79 work: 2 80 work: 2 79 work: 2 76 work:

15 The computational work is calculated based on the expected amount of calculated hashes Hash function: any function that can be used to map data (x) of arbitrary size to data of fixed size (y): hash(x) = y x y Cryptographic hash function: non-reversible hash function (and ideally some other features): Given y, very hard to find x x y 15

16

17 Mining (Proof of Work): Find solution to a mathematical puzzle that can only be solved by brute force (trial & error) 1. Immutability: Set order of transactions (changing anything requires to re-mine ) 2. Consensus based on amount of mining work 17

18

19 Mining is a race: As a miner you want to be the first to find the solution to get a reward (tx fees and block reward) <Data> PoW mining <coinbase tx> <Data> 19

20 The blockchain is build of blocks: chunks of data Block k - 1 Block k Block k + 1 Header hash(<data>) prev Hash hash(<data>) prev Hash hash(<data>) prev Hash Body <Data> <Data> <Data> 20

21 Changing data in a previous block would require an attacker to redo the Proof-of-Work of all later blocks 21

22 In Bitcoin the average block number is 10 minutes The target value is dynamically adjusted (every 2016 blocks) 22

23 The data in the blocks is created by transactions and sent to peers Transaction: Send 3 Bitcoin from Alice to Bob 23

24 Every node in the network checks if a transaction is valid transaction receiver address hash of prev. tx sender public key sender signature Valid signature No overspending No double-spending cryptocurrency 24

25 How do you own a Bitcoin? coinbase transaction miner address transaction receiver address UTXO transaction receiver address hash of prev. tx hash of prev. tx cryptocurrency sender public key sender public key sender signature sender signature cryptocurrency cryptocurrency A Bitcoin is a chain of signed transactions (i.e. every coin has a history). The owner of a Bitcoin owns the private key corresponding to an unspent transaction output (UTXO). 25

26 How to cheat/attack? Pool of unconfirmed transactions transaction A pays B transaction A pays A Send conflicting transaction Which own will end up in the blockchain? 26

27 Wait for confirmations Block k Block k + 1 transaction transaction <Data> 0 confirmations 1 confirmation 2 confirmations 27

28 Short summary: The main building blocks of Bitcoin are: - Peer-to-peer network - Public ledger - Digital Signatures - Proof-of-Work (Mining) - Blockchain 28

29 How to participate in the Bitcoin network? Download a wallet Get Bitcoins (e.g. from a friend or from an exchange such as kraken.com) 29

30 Part I: Bitcoin: Idea, Basics, Technology Part II: Altcoins, Use cases, Blockchain applications 30

31 Quite early, people realized that Bitcoin is just one application build on blockchain technology Appearance of Altcoins Image source: See also 31

32 Use cases of Altcoins financial records domain name registration voting medical records artificial intelligence? 32

33 Peer-to-peer network 33

34 Peer-to-peer network <Data> <Data> <Data> <Data> <Data> <Data> <Data> <Data> 34

35 Image source:

36 Financial transactions Arbitrary decentralized applications Bitcoin Blockchain 1.0 Ethereum Blockchain 2.0 Image source:

37 Use case of Ethereum: Blockchain-based smart contracts: programming code executed via blockchain technology tamper-proof code without any possibility of downtime, censorship, fraud or third-party interference (ethereum.org) main programming language: Solidity (online IDE at 37

38 Traditional crowdfunding centralized crowdfunding platform (e.g. kickstarter.com) needs trust all-or-nothing Project (e.g. smartwatch) needs trust backers Image source: - money really send to the project? - transparency - potentially high fees 38

39 Ethereum-based crowdfunding (see for an implementation in Solidity) transaction Block k - 1 Block k Block k + 1 <Data> <Data> <Data> transaction transaction decentralized crowdfunding platform based on Ethereum trustless: all-or-nothing Project (e.g. smartwatch) needs trust - decentralized (no single point of failure) - guaranteed execution of the transfer - transparency - immutable - potentially lower fees backers 39

40 Blockchain Technology and AI? 40

41 (Very simplified) comparison between AI and Blockchain Technology Artificial Intelligence Blockchain Technology probabilistic deterministic black box transparent computationally complex algorithms lightweight programs (smart contracts) See also YouTube talk Blockchain + AI = Decentralized Artificial Intelligence by Siraj Raval ( 41

42 How AI might improve blockchain technology AI Blockchain Scalability More useful mining algorithm Intelligent interfaces 42

43 How blockchain technology might improve AI Blockchain AI Huge amount of data / easy collection of data Transparency (public history of actions audit trail) Increase trust Marketplace for data/models 43

44 Example Blockchain AI projects (most of these projects are at an early stage of development) Decentralized privacy-preserving machine learning: (openmined.org) Identity validation of AI Agents ( AI as a service (monetarize AI) ( 44

45 My PhD thesis Blockchain-based smart contracts for the secure coordination of robot swarms 45

46 A blockchain is a decentralized database where everyone can participate Peer-to-peer network 46

47 A blockchain is a decentralized database where everyone can participate Robot peer-to-peer network 47

48 Byzantine robots show arbitrary faulty or malicious behavior Motor broken! Infrared module broken! GPS connection lost! Programming code not updated! Tamper with messages! laboratory experiments real-world applications 48

49 Goal: Develop a framework for programming secure robot swarms For more details, see: V.Strobel, E. Castello Ferrer, M. Dorigo Managing Byzantine Robots via Blockchain Technology in a Swarm Robotics Collective Decision Making Scenario. To appear in Proceedings of the 17th Conference on Autonomous Agents and MultiAgent Systems. International Foundation for Autonomous Agents and Multiagent Systems (AAMAS 2018). 49

50 Research ideas / open Research questions Can the Proof-of-Work be replaced by something more useful (e.g. training of a neural network)? What are use cases for blockchain technology? Possibilities and limitations of combining AI technologies and blockchain technology? 50

51 What could you do? Build a decentralized (AI?) application with Ethereum 51

52 Further material Mastering Bitcoin by Andreas M. Antonopoulos ( Coursera online course ( Cryptocurrency news ( 52

53 Thank you! Volker Strobel