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CS1951 L Spring 2019

Course Introduction. CS1951 L Spring 2019. 24 January 2019. Maurice Herlihy Brown University. Bitcoin is in the news …. and I, for one, just can’t look away …. Irrational exuberance. “Buy a stock, if it goes up, sell it, if it goes down, don't buy it .”. Yogi Berra. BTC at $20K.

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CS1951 L Spring 2019

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  1. Course Introduction CS1951 L Spring 2019 24 January 2019 Maurice Herlihy Brown University

  2. Bitcoin is in the news …. and I, for one, just can’t look away …

  3. Irrational exuberance “Buy a stock, if it goes up, sell it, if it goes down, don't buy it.” Yogi Berra

  4. BTC at $20K BTC today? Our mission here

  5. true crime

  6. vanishing millions

  7. financial irregularities

  8. not just Bitcoin

  9. mysterious identities

  10. sex, drugs, rock-n-roll

  11. This course is not about Bitcoin

  12. This talk is not about Bitcoin It’s about blockchains.

  13. This talk is not about Bitcoin It’s about blockchains. From a non-political, non-romanticized scientific perspective.

  14. Grade Breakdown

  15. Topics we will study Programming languages Buggy programs Data structures Distributed consensus protocols Cookbook Crypto

  16. Follow the Money Millions, billions at stake Every author, every opinion … Who pays them? What is their interest? Not dishonest, but not disinterested.

  17. Real innovation usually intrudes from outside a community … Would this paper have been accepted to a mainstream DC conference in 2008? Now multi-billion dollar industry What relation to classical distributed computing?

  18. The Blockchain Universe’s attempt to re-invent distributed computing did not always go well …

  19. On the other hand … The Distributed Computing Universe’ s bid for respect and influence sometimes fell short …

  20. Abstraction:Distributed Ledger Append-only list of events Not just financial Everyone agrees on content Tamper-proof!

  21. Alice’s Trading Company Trading Engine retail wholesale Alice has a concurrency problem

  22. Alice’s Trading Company Trading Engine retail wholesale Global lock is too coarse

  23. Alice’s Trading Company Trading Engine retail wholesale Fine-grained locks too hard

  24. Swapped out back at Locks don’t scale ??? ???

  25. Universal Lock-Free Construction Operations that want to happen This happened Operations that happened, in order This happened This happened This happened This happened root This happened

  26. Universal Lock-Free Construction This happened This happened This happened This happened This happened consensus This happened

  27. Consensus: Each Thread has a Private Input

  28. They Communicate

  29. They Agree on One Thread’s Input

  30. Agreement: they agree on the same value Termination: non-faulty parties decide in finite time Validity: they agree on someone’s proposal

  31. Universal Lock-Free Construction This happened Ledger part is simple, sequential This happened This happened This happened This happened consensus This happened

  32. Universal Lock-Free Construction This happened Ledger part is simple, sequential This happened This happened Concurrency, fault-tolerance restricted to here This happened This happened consensus This happened

  33. Get operation No, try again Did I win consensus? Yes Deal with it Generate response

  34. Cryptographic Hash Functions Easy Hard

  35. Cryptographic Hash Functions Hard to reconstruct x from H(x) Easy “preimage resistance” Hard

  36. Cryptographic Hash Functions Given Hard to find

  37. Cryptographic Hash Functions Given Hard to find x’ such that H(x’) = H(x) Hard to find “2nd preimage resistance”

  38. Cryptographic Hash Functions Hard to find

  39. Cryptographic Hash Functions Hard to find Hard to find any x,x’ such that H(x’) = H(x) “collision resistance”

  40. The Universal Construction This happened |hash Each entry has predecessor’s hash This happened | hash Can be audited This happened | hash This happened This happened consensus This happened

  41. Alice has a frozen yogurt business Her business is in trouble Shipments arrive melted

  42. Alice’s Supply Chain What Bob said! Bob’s truck Carol’s factory I never transported that yogurt It was melted when I got it from Carol It was OK when I delivered it to Alice

  43. Ledger in Cloud Sensors Bob and Carol

  44. Consensus Again

  45. Crash Failures

  46. Byzantine Failures

  47. Supply Chain Blockchain -C at 13:00 -C at 13:10 -C at 13:20 Sensor reading Sensor reading PBFT Sensor reading

  48. Supply Chain Blockchain -C at 13:10 -C at 13:20 Carol handoff to Bob, 13:30 Carol Signed Bob Signed signatures

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