A Blockchain ProjectVincent Gramoli

(Collaboration with Ingo Weber and Rob van Glabbeek)

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Bitcoin nodes

source: https://bitnodes.21.co/

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What is blockchain?

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• Abstraction to represent the state of a ledger

• Each transaction transfers from one account to another a quantity of coins and gets recorded in a ledger

• Information can only be appended to the ledger forever (it cannot be modified)

genesis

How does blockchain work?

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• On a large-scale network

• Any computer node can issue a transaction

• Other nodes, miners, include it in a block

• They propose to append the block to the chain

• Nodes reach consensus on the block to append

Logical overlay

current blockchain

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genesis

New transaction

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tx

current blockchain

genesis

Gossip-based protocol

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tx

tx

tx

current blockchain

genesis

Gossip-based protocol

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tx

tx

tx

tx

tx

current blockchain

genesis

Mining into a block

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tx

tx

tx

current blockchain

genesis

miner miner

tx tx

Mining into a block

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tx

b2

tx

tx

b1

current blockchain

genesis

miner miner

Consensus

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b2 b1

current blockchain

genesis

b2 ok! b1 ok!

tx

tx

tx

Consensus

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b2 b1

b1

b1

b1 ok!

b1 ok!

b2 b2 ok!

current blockchain

genesis

b2 ok! b1 ok!

Consensus

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b2 b1

b1

b1

b1 ok!

b1 ok!

b2 b2 ok!

current blockchain

genesisb2

b1

b2 ok! b1 ok!

Consensus

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b2 b1

b1

b1

b1 ok!

b1 ok!

b1 b1 ok!

current blockchain

genesisb2

b1

b1 ok!

Consensus

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b1 b1

b1

b1

b1 ok!

b1 ok!

b1 b1 ok!

b1 ok!

current blockchain

genesis b1

b1 ok!

Consensus

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Applications assume that the block i is decided (and its transactions are committed) when the blockchain depth reaches i+k

genesis

1 i i+1 i+k-1

i+k

0

decided block undecided block

The Blockchain Anomaly [NG’16]

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We showed under realistic assumptions that in a private chain, there is no k sufficiently large for the application to work correctly

The Blockchain Anomaly [NG’16]

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b1 b1

b1

b1

b1 ok!

b1’ ok!

b1 b1 ok!

b1 ok!

current blockchain

genesisb1’

b1

b1 ok!

The Blockchain Anomaly [NG’16]

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b1 b1

b1

b1 b1’, b2’, …, bk’ ok!

b1

b1, b2, …, bk-1

current blockchain

genesisb1’

b1

bk-1'

bk-1

bk'

b1, b2, …, bk-1

b1, b2, …, bk-1

b1, b2, …, bk-1

The Blockchain Anomaly [NG’16]

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b1 b1

b1

b1 b1’, b2’, …, bk’ ok!

b1

current blockchain

genesis b1’ bk-1' bk'

b1’, b2’, …, bk’ ok!

b1’, b2’, …, bk’ ok!

b1’, b2’, …, bk’ ok!

Next Steps

Replaying the blockchain anomaly on the network of R3, and implementing a solution

Understanding the assumptions necessary to transfer across blockchains

Taste-Of-Research: building a crowd-funding (DAO) application based on smart contract

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References• [Nak’08] S. Nakamoto, “Bitcoin: a peer-to-peer electronic cash

system,” 2008. http://www.bitcoin.org

• [Woo’14] G. Wood, “Ethereum: A secure decentralised generalised transaction ledger”. 2014. https://github.com/ethereum/wiki/wiki/White-Paper

• [NG’16] C. Natoli, V. Gramoli. The Blockchain Anomaly. TechRep. arXiv 1605.5438.

• [XPZ+16] X. Xu, C. Pautasso, L. Zhu, V. Gramoli, S. Chen, A. Ponomarev, and A. B. Tran, “The blockchain as a software connector,” in Proceedings of the 13th Working IEEE/IFIP Conference on Software Architecture (WICSA), 2016.

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