Slides for Blockchain Developers Meetup, Moscow, May 2016

1. Moscow Blockchain Devs Meetup
Some Open Problems in Blockchains
Alexander Chepurnoy
(aka kushti)
@chepurnoy
IOHK Research

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. The talk is about
● What are open problems in blockchains
● How can we solve them

4. Current State
● 1.33 well understood systems working
● Bitcoin
● partly Ethereum
● A lot of work-in-progress around

5. Bitcoin
● highly centralized
● scalability is questionable
● well studied(in both theory & practice)

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. Bitcoin Consensus Protocol
● „The Bitcoin Backbone Protocol:Analysis and Applications“
● „Analysis of the Blockchain Protocol in Asynchronous
Networks“

8. Better PoW
● Equihash - memory-hard PoW (ZCash)
● Permacoin – proofs of retrievability for static dataset
● Rollerchain – proofs of posession of state snapshots

9. Blockchain Pruning

10. Rollerchain
● http://arxiv.org/abs/1603.07926
● „A Prunable Blockchain Consensus Protocol Based on
Non-Interactive Proofs of Past States Retrievability“

11. Rollerchain
● Only last n full blocks to be stored collectively
● and n state snapshots
● Each miner stores k state snapshots

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. Proof-of-Stake
● Formalization is coming
● Hopefully in 2016
● Problems: randomness, forking, timing

14. Scalability
● Move things off-chain
● Sidechains
● Avoid all the transactions execution(RsCoin)

15. Offchain
● Lightning Network(ThunderNetwork)
● Offchain contracts(SMC/SMP)

16. Smart Contracts
● Ethereum isn't scalable
● Hawk
● Enigma

17. Anonymity
● A lot of schemes proposed
● Most of them are probably broken or not practical
● Cryptonote
● ZCash
● Upcoming survey from Bernardo David

18. Applications
● Randomness
● System designs: „The Blockchain as a Software
Connector“
● Protocols study

19. Primitives
● Post-quantum digital signatures: BLISS, NTRU

20. Trivial Things
● Specially crafted database
● Formalized code (not formal model)
● Extensive testing at least :)

21. Conclusion
● We have a lot of open problems!
● A lot of results are to be released soon

22. Questions?
Twitter: @chepurnoy
Mail: kushti@protonmail.ch