On Private Blockchains, Technically

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  • Blockchain Hackathon Moscow

    Alexander Chepurnoy

    On Private Blockchains, Technically

  • My Background

    Java then Scala development Distributed / P2P systems development Nxt Core Developer SmartContract.com / Secureae.com cofounder/dev Consensus Research member Scorex project

  • Fields of Interest

    Distributed & P2P systems Blockchain Tech Functional Programming (Haskell / Scala) Formal Methods (model checking / Coq) Finite State Machines and some other topics in CS

  • The Design of a Cryptocurrency

    P2P Network Persistent distributed fully-replicate database (aka

    Blockchain) Transactions operating with tokens grouped within blocks,

    a block is a database version Consensus algorithm Optional: additional layers on top of transactional

    layer(mesages, colored coins, code)

  • A Blockchain Structure

  • Consensus About Blockchain

    Proof-of-Work Proof-of-Stake Hybrid: Proof-of-Work+Proof-of-Activity, Proof-of-


  • BlockTree

  • Blockchain As A Database

    Persistent(versioned) database Genesis state initial verion of the database Block as state modifier: State(h) * Block State(h+1) Very weak consistency!

  • PoW-based Trustless Database

    If adversarial hashing power is less than 50% : replicated log and state a probability of transaction exclusion from a blockchain is

    going down exponentially with time a probability of valid trransaction non-inclusion into a

    blockchain is going down exponentially with time node's state divergence from a canonical one(majority has)

    is going down exponentially with time(if exists) dependless on who mined a concrete block

  • Private Blockchains

    want to get maximum from the trustless db model have non-monetary purposes, usually limited number of participants(or just miners)

  • Private Blockchains

    are proposed for:

    art objects ownership history real estate ownership history (chain of title) Inter-banks procedures(clearing etc) etc

  • Implementation

    consensus protocol transactional model incentives model

  • Consensus PoW

    Not fair(richer parties will take control over a network soon) Attacks via outsourcing work to Bitcoin miners Why art gallery or real estate agency needs for a lot of

    expensive special hardware in addition to the database software?

  • Consensus - PoS

    Generation rights Predefined distribution of generation rights Works in practice for few years Some security investigations are done...

    but more needed! As well as formalizations.

  • Trusted Random Beacon

    Bitcoin / Nxt / other public blockchain could be used as a trusted source of randomness, to chose next block generator

    Blocks frequency is the same in both chains (SPV) client is needed to be inbuilt in a node

  • Byzantine Agreement Scheme

    A lot of well-known formalized solutions to the distributed commit problem

    Up to ~5000 participants Verification could be costly

  • Transactional Model

    Should be suitable for max performance Min transaction size Prunable state Bitcoin's transactions with multiple inputs & outputs and

    scripts attached to both sides probably isn't the most suitable model for many non-monetary cases

  • Incentives Model

    Long-term security

    Why to participate in a network? Why to run a fullnode? Why to generate a block? Why to include transactions in a block?

  • Better Quality of Blockchain Impls

    Modular approach Safer languages(Scala/Ocaml, Haskell, Idris/Coq) Formal methods usage Prototypes before products


    The cryptocurrency engine in less than 4K lines of Scala code

    To make proof-of-concepts FAST! Compact code Not production-ready CC0 license

  • Lagonaki Release

    100% Proof-of-stake Simplified account-based transaction model Simple payments only Curve25519 for signing JSON API Command-line client

  • Under The Hood:

    Scala Akka MapDB Spray Play Json Scalatest Logback

  • Questions?

    Articles: On Private Blockchains, Technically

    http://chepurnoy.org/blog/2015/11/on-private-blockchains-technically/ On the Way to a Modular Cryptocurrency, Part 1: Generic Block

    Structure http://chepurnoy.org/blog/2015/10/on-the-way-to-a-modular-cryptocurrency-part-1-generic-block-structure/

    A Cryptocurrency Architecture


    Mail: kushti@protonmail.ch


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