Distributed Ledger Technology: Beyond the Blockchain Hype

Distributed Ledger Technology: Beyond the Blockchain Hype

Talk given at Darwin College Science Seminar. Covers the science behind distributed ledgers, among other things.

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KC Sivaramakrishnan

November 23, 2017
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Transcript

  1. Distributed Ledger Technology: Beyond the Blockchain Hype KC Sivaramakrishnan Computer

    Laboratory
  2. What is it worth today? https://www.coindesk.com/price/

  3. What is it worth today? https://www.coindesk.com/price/ 0.1 btc

  4. What is it worth today? https://www.coindesk.com/price/ 0.1 btc

  5. What is it worth today? https://www.coindesk.com/price/ 0.1 btc 55

  6. None
  7. That’s ~$5000 now!

  8. None
  9. In this talk… • Basics of blockchain: the technology that

    underlies bitcoin • Other uses of distributed ledger technology • My research into decentralised database technology
  10. Cryptocurrencies

  11. Cryptocurrencies • Digital currencies are mediums of exchange that are

    created and stored in a virtual format ★ Not backed by Government (Ponzi scheme?)
  12. Cryptocurrencies • Digital currencies are mediums of exchange that are

    created and stored in a virtual format ★ Not backed by Government (Ponzi scheme?) • No centralised authoritative ledger — Distributed Ledger/Blockchain ★ Everyone collaborates to everyone’s benefit
  13. Cryptocurrencies • Digital currencies are mediums of exchange that are

    created and stored in a virtual format ★ Not backed by Government (Ponzi scheme?) • No centralised authoritative ledger — Distributed Ledger/Blockchain ★ Everyone collaborates to everyone’s benefit • Very nice properties ★ Transparency: all transactions are public ★ Anonymity: owners of accounts remain anonymous ★ Integrity: No one can tamper with the ledger without leaving evidence
  14. Distributed Ledger Head Genesis

  15. Distributed Ledger Head Genesis Network

  16. Hash Functions "A cryptographic hash function is a hash function

    which is considered practically impossible to invert, that is, to recreate the input data from its hash value alone.
  17. Distributed Ledger T0 Head B0 T1 Hash (B0) T2 Hash

    (B1) T3 Hash (B2) T4 Hash (B3) B1 B2 B3 B4
  18. Transactions A:100 B:100 C:100 Head B0 A->B:50 A->D:30 Hash (B0)

    T2 Hash (B1) T3 Hash (B2) T4 Hash (B3) B1 B2 B3 B4
  19. Transactions A:100 B:100 C:100 Head B0 A->B:50 A->D:30 Hash (B0)

    T2 Hash (B1) T3 Hash (B2) T4 Hash (B3) B1 B2 B3 B4 A->B:10 Hash (B4)
  20. Transactions A:100 B:100 C:100 Head B0 A->B:50 A->D:30 Hash (B0)

    T2 Hash (B1) T3 Hash (B2) T4 Hash (B3) B1 B2 B3 B4 A->B:10 Hash (B4) Network
  21. Transactions A:100 B:100 C:100 Head B0 A->B:50 A->D:30 Hash (B0)

    T2 Hash (B1) T3 Hash (B2) T4 Hash (B3) B1 B2 B3 B4 A->B:10 Hash (B4) Network
  22. Transactions A:100 B:100 C:100 Head B0 A->B:50 A->D:30 Hash (B0)

    T2 Hash (B1) T3 Hash (B2) T4 Hash (B3) B1 B2 B3 B4 A->B:10 Hash (B4) Network
  23. Forks A:100 B:100 C:100 B0 A->B:50 A->D:30 Hash (B0) T2

    Hash (B1) T3 Hash (B2) T4 Hash (B3) B1 B2 B3 B4 Network T5 Hash (B2) T6 Hash (B5) B5 B6
  24. Consensus: who extends the chain?

  25. Consensus: who extends the chain? • Single authoritative leader? ★

    Defeats decentrality ★ Malicious?
  26. Consensus: who extends the chain? • Single authoritative leader? ★

    Defeats decentrality ★ Malicious? • Make all the nodes “agree” on the authoritative fork ★ Proof-of-work vs proof-of-stake to minimise forks ★ Longest fork is the authoritative one
  27. None
  28. Proof-of-work is wasteful!

  29. Proof-of-work is wasteful! • All for what? ★ Bitcoin ~=

    7 tx/s, >10 minutes to confirm the transaction ★ Visa ~= 125000 tx/s, confirmation time of few seconds
  30. A cunning interlock • Bitcoin is a cunning crafted system

    that combines 40 years of academic research! ★ Distributed consensus protocols ★ Cryptographic hashing ★ Peer-to-peer anonymous digital signatures • But we can recombine these concepts in many other interesting ways with different constraints
  31. Blockchain Apps

  32. Blockchain Apps • Smart contracts — code instead of transactions

    ★ Decentralized autonomous organizations
  33. Blockchain Apps • Smart contracts — code instead of transactions

    ★ Decentralized autonomous organizations • Filecoin — distributed archival storage ★ Distributed Dropbox ★ Earn filecoin for storing other’s files
  34. Blockchain Apps • Smart contracts — code instead of transactions

    ★ Decentralized autonomous organizations • Filecoin — distributed archival storage ★ Distributed Dropbox ★ Earn filecoin for storing other’s files • Land registry ★ Sweden, Honduras, UK??
  35. Blockchain Apps • IPFS — Interplanetary File System ★ A

    way to store and share files ★ decentralized www
  36. Blockchain Apps • IPFS — Interplanetary File System ★ A

    way to store and share files ★ decentralized www • Catalan Referendum ★ Declared as illegal by Spanish Govt ✦ All websites carrying info blocked. ISPs raided. ★ Where to vote? ★ Information hosted on IPFS!
  37. My research: Ignore consensus?

  38. My research: Ignore consensus? Merge

  39. My research: Ignore consensus? • Distributed version control system: Git,

    Mercurial, Darcs ★ Contents of blocks is files, directory structure, etc. ★ Concurrent modifications without synchronisation! ★ Tamper evident file system ★ Provenance Merge
  40. Merge This Seminar is held in 1 Newnham Terrace Today

    is Friday
  41. Merge This Seminar is held in 1 Newnham Terrace Today

    is Friday This Seminar is held in 1 Newnham Terrace Today is Thursday Alice
  42. Merge This Seminar is held in 1 Newnham Terrace Today

    is Friday This Seminar is held in 1 Newnham Terrace Today is Thursday Alice This Seminar is held in Richard King room Today is Friday Bob
  43. Merge This Seminar is held in 1 Newnham Terrace Today

    is Friday This Seminar is held in 1 Newnham Terrace Today is Thursday Alice This Seminar is held in Richard King room Today is Friday Bob This Seminar is held in Richard King room Today is Thursday Merge Bob
  44. Research Themes • Can we go beyond files? ★ Convergent

    replicated data types
  45. Research Themes • Can we go beyond files? ★ Convergent

    replicated data types • How do you know that the merge function is correct? ★ Intent preservation, convergence ★ Program verification for correctness by construction
  46. Research Themes • Can we go beyond files? ★ Convergent

    replicated data types • How do you know that the merge function is correct? ★ Intent preservation, convergence ★ Program verification for correctness by construction • What about scalability and applicability? ★ Irmin (http://irmin.io) — a blockchain based distributed database ★ Pure OCaml => Can compile to Desktops, Cloud, Raspberry Pi, JavaScript
  47. Questions?