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Computing for Decentralized Systems
Alejandro Avilés (@OmeGak) 7th ~ 8th March 2018
Attribution-NonCommercial-ShareAlike 4.0 International (CC BY-NC-SA 4.0)
Computing for Decentralized Systems Alejandro Avils (@OmeGak) 7th ~ - - PowerPoint PPT Presentation
Computing for Decentralized Systems Alejandro Avils (@OmeGak) 7th ~ - - PowerPoint PPT Presentation
Computing for Decentralized Systems Alejandro Avils (@OmeGak) 7th ~ 8th March 2018 Attribution-NonCommercial-ShareAlike 4.0 International (CC BY-NC-SA 4.0) Distributed Systems Distribute /d str b.ju t/ To give something out to
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Distribute /dɪˈstrɪb.juːt/ To give something out to several people, or to spread or supply something.
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Distributed system Hardware or software components located at networked computers communicating and coordinating their actions to achieve a common goal only by passing messages.
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Advantages
Fault tolerance Sharing resources Lower latency
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Complications
Concurrency No global clock Independent failures
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Security model
Interfaces Cryptography Control and trust
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Role-based architectures
Client-server Peer-to-peer
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Decentralized Systems
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Decentralize /ˌdiːˈsen.trə.laɪz/ To move the control of an organization or government from a single place to several smaller
- nes.
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Types of (de)centralization
Architectural (Location) Political (Authority) Logical (Consensus)
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Centralized systems
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Decentralized systems
https://youtu.be/C2vgICfQawE
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Decentralization in Nature
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Decentralization in Society
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Decentralization in Computing
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Consensus and Byzantine Fault Tolerance
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Consensus /kənˈsen.səs/ A generally accepted opinion or decision among a group of people.
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Network splits
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Strong consistency
Consensus algorithms Authority? Trust?
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The two generals problem
Attack at dawn ACK ACK' ACK''
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The Byzantine generals problem
🤟 🤟
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Scalability of trust
Trusted generals Complexity of trust O(N2) Centralization of authority
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Governance, Economics, and Proof-of-Work
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Governance /ˈɡʌv.ɚ.nəns/ The way that organizations or countries are managed at the highest level.
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Economics /ˌiː.kəˈnɑː.mɪks/ The social science that studies the production, distribution, and consumption of goods and services focusing on the behaviour and interactions
- f economic agents.
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The siege
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Attack or retreat?
🤟 🤟
Let's go! Go go go! Retreat! Abort! Let's go back! Nope!
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Let's vote
Retreat!
🤟 🤟
Abort! Let's go back! Let's go! Go go go! Nope! Retreat!
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No central authority
Attack!
🤟 🤟
x9 Abort! Let's go back! Let's go! Go go go! Nope! Retreat!
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Treason ensues!
🤟 🤟
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Proof of Work~ish
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Economics in war
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Expensive voting
Consensus!
🤟 🤟
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Dominant strategy
rewardi = (loot / N) + valueOfStayingAlivei
- (voteCost * votesi)
🤟
voteCost > ???
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Breaking the equilibrium?
🤟
???
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Bitcoin and the Blockchain
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Bitcoin /ˈbɪt.kɔɪn/ A purely peer-to-peer version of electronic cash that allows online payments to be sent directly from
- ne party to another without going through a
financial institution.
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What is Bitcoin, really? 🤕
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A database*
Unrestricted read Unrestricted write * Append only Blockchain: Linked list of state updates
≃
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Bitcoin network
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Bitcoin protocol
Describes valid blocks Will others take my block? Should I take this block?
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Bitcoin =
Measure of reward Granted to block issuer Described in the protocol New valid block arrives
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Bitcoin transactions
Transmission of ownership Described in the protocol Broadcasted Validated by peers Inserted in blocks
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A few problems
🤟 ⚡
Not a cost-free service Not everybody is trustworthy
💪
Reward's worth is subjective
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So... WHY does this work, really? 🤰
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Utility and cost
Permission-less Resilient Not cost-free
≃
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The mining game
Valid blocks are rewarded Miners use CPU cycles They produce valid blocks
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Validity chain
Is this new block valid? Validators require past blocks
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Reward ledger
A database of transactions Anybody can broadcast Nobody can censor * Everybody can read
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Bitcoin as currency =
Portable Scarce Block creation is rate-limited Reward is not infinite 10' 10'
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Censorship resistance
🤟 🤟
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Sybil attack resistance
Power into valid blocks Honest nodes make profit Power into invalid blocks Malicious nodes gain nothing
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Race condition resistance
The longest chain rule Most work invested Adjustable difficulty Rate-limits updates 10' 10' 10' 10' 10'
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Proof of Work in Bitcoin
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Block hashes
Double SHA-256 Hash of the previous valid block Valid bitcoin transactions Nonce
+ +
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Block mining
Valid hash: 0000000000000000001b13... Nonce increases CPU used in SHA-256
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Tampering with the past
Blocks can be altered locally Hashes become invalid Invalid blocks must be re-mined Attacker must spend CPU
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Single version of truth
Honest chain keeps growing Attacker must outrun network 51% attack would allow this * 10' ?'
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Bitcoin applications beyond cash
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Ethereum, Smart Contracts, and Decentralized Applications
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Contract /ˈkɑːn.trækt/ A legal document that states and explains a formal agreement between two different people or groups,
- r the agreement itself.
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Ethereum
A computer * Turing-complete language Arbitrarily complex transactions *
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Smart Contracts
Agreement between parties Protocol to perform
- n promises
Breach is expensive
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Contract design
Who can resolve disputes? Reactive enforcement Proactive enforcement
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Decentralizing contracts
Arbiter replaced by the blockchain Reduced need for trust in humans * Higher degree of automation
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Decentralized apps
Decentralized computing Crowdsourced knowledge Decentralized insurance
Golem Gnosis Etherisk
Decentralized business Decentralized court systems Decentralized digital nations?
Colony Aragon
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