Moscow Blockchain Devs Meetup

Some Open Problems in Blockchains

Alexander Chepurnoy(aka kushti)@chepurnoyIOHK Research

Background

programming since 1996

p2p systems with Scala/Akka

Nxt core developer

Consensus Research

smartcontract.com cofounder(left)

Scorex since late 2014

IOHK Research

The talk is about

What are open problems in blockchains

How can we solve them

Current State

1.33 well understood systems working

Bitcoin

partly Ethereum

A lot of work-in-progress around

Bitcoin

highly centralized

scalability is questionable

well studied(in both theory & practice)

Troughput (TPS)

7 ??? no

2-3 in fact

1/600 in worse casehttps://www.reddit.com/r/Bitcoin/comments/3cgft7/largest_transaction_ever_mined_999657_kb_consumes/

Bitcoin Consensus Protocol

The Bitcoin Backbone Protocol:Analysis and Applications

Analysis of the Blockchain Protocol in Asynchronous Networks

Better PoW

Equihash - memory-hard PoW (ZCash)

Permacoin proofs of retrievability for static dataset

Rollerchain proofs of posession of state snapshots

Blockchain Pruning

Rollerchain

http://arxiv.org/abs/1603.07926

A Prunable Blockchain Consensus Protocol Based on Non-Interactive Proofs of Past States Retrievability

Rollerchain

Only last n full blocks to be stored collectively

and n state snapshots

Each miner stores k state snapshots

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

Proof-of-Stake

Formalization is coming

Hopefully in 2016

Problems: randomness, forking, timing

Scalability

Move things off-chain

Sidechains

Avoid all the transactions execution(RsCoin)

Offchain

Lightning Network(ThunderNetwork)

Offchain contracts(SMC/SMP)

Smart Contracts

Ethereum isn't scalable

Hawk

Enigma

Anonymity

A lot of schemes proposed

Most of them are probably broken or not practical

Cryptonote

ZCash

Upcoming survey from Bernardo David

Applications

Randomness

System designs: The Blockchain as a Software Connector

Protocols study

Primitives

Post-quantum digital signatures: BLISS, NTRU

Trivial Things

Specially crafted database

Formalized code (not formal model)

Extensive testing at least :)

Conclusion

We have a lot of open problems!

A lot of results are to be released soon

Questions?

Twitter: @chepurnoyMail: kushti@protonmail.ch