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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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