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Some Open Problems in Blockchains

Slides for Blockchain Developers Meetup, Moscow, May 2016

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Some Open Problems in Blockchains

  1. 1. Moscow Blockchain Devs Meetup Some Open Problems in Blockchains Alexander Chepurnoy (aka kushti) @chepurnoy IOHK Research
  2. 2. Background ● programming since 1996 ● p2p systems with Scala/Akka ● Nxt core developer ● Consensus Research ● smartcontract.com cofounder(left) ● Scorex since late 2014 ● IOHK Research
  3. 3. The talk is about ● What are open problems in blockchains ● How can we solve them
  4. 4. Current State ● 1.33 well understood systems working ● Bitcoin ● partly Ethereum ● A lot of work-in-progress around
  5. 5. Bitcoin ● highly centralized ● scalability is questionable ● well studied(in both theory & practice)
  6. 6. Troughput (TPS) ● 7 ??? no ● 2-3 in fact ● 1/600 in worse case https://www.reddit.com/r/Bitcoin/comments/3cgft7/largest_trans
  7. 7. Bitcoin Consensus Protocol ● „The Bitcoin Backbone Protocol:Analysis and Applications“ ● „Analysis of the Blockchain Protocol in Asynchronous Networks“
  8. 8. Better PoW ● Equihash - memory-hard PoW (ZCash) ● Permacoin – proofs of retrievability for static dataset ● Rollerchain – proofs of posession of state snapshots
  9. 9. Blockchain Pruning
  10. 10. Rollerchain ● http://arxiv.org/abs/1603.07926 ● „A Prunable Blockchain Consensus Protocol Based on Non-Interactive Proofs of Past States Retrievability“
  11. 11. Rollerchain ● Only last n full blocks to be stored collectively ● and n state snapshots ● Each miner stores k state snapshots
  12. 12. Rollerchain ● New node can download a historical snapshot ● Fullblocks not needed for mining could be thrown away ● Blockheaders are to be stored forever, so must be small
  13. 13. Proof-of-Stake ● Formalization is coming ● Hopefully in 2016 ● Problems: randomness, forking, timing
  14. 14. Scalability ● Move things off-chain ● Sidechains ● Avoid all the transactions execution(RsCoin)
  15. 15. Offchain ● Lightning Network(ThunderNetwork) ● Offchain contracts(SMC/SMP)
  16. 16. Smart Contracts ● Ethereum isn't scalable ● Hawk ● Enigma
  17. 17. Anonymity ● A lot of schemes proposed ● Most of them are probably broken or not practical ● Cryptonote ● ZCash ● Upcoming survey from Bernardo David
  18. 18. Applications ● Randomness ● System designs: „The Blockchain as a Software Connector“ ● Protocols study
  19. 19. Primitives ● Post-quantum digital signatures: BLISS, NTRU
  20. 20. Trivial Things ● Specially crafted database ● Formalized code (not formal model) ● Extensive testing at least :)
  21. 21. Conclusion ● We have a lot of open problems! ● A lot of results are to be released soon
  22. 22. Questions? Twitter: @chepurnoy Mail: kushti@protonmail.ch

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