researches on blockchain “networks” · •a public blockchain “network” simulator –...
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Researches onBlockchain “Networks”
Kazuyuki ShudoTokyo Tech
首藤一幸東京工業大学
IEEE Tokyo Blockchain WorkshopJuly 29th, 2019
Tokyo Tech
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Cryptocurrency anda public blockchain supporting it
TX
Hash valueBlock
TX TX TX
Hash valueBlock
TX TXA crypto-graphichash function
A hash chain of blocks
A peer-to-peer (P2P) network of participating nodes= An application-levelnetwork
Node (miner)
https://bitnodes.earn.com/9,200 nodes on Bitcoin network
• A distributed system supporting cryptocurrencies– Bitcoin’s market capitalization is
US$ 180B.– Decentralized
• Expected applications– Essentially, time stamp authority or
notary office– Supply chain mgmt., traceability,
governance process such as voting, automatic operation of organizations, …
• Transactions and blocks are broadcasted to all the nodes.
• All the nodes store the identical ledger.• Nodes race each other for producing a block.
‐> Mining in Proof of Work protocol
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Technologiessupporting blockchain
• Cryptography– Public‐key cryptography,
digital signature, cryptographic hash function, random number generation, …
• Distributed systems– Peer‐to‐peer networks,
flooding, replication, consistency, consensus algorithms, …
What public (permissionless) blockchains achieved– Inconsistency (double spending) prevention, and alteration prevention– Fault tolerance– Transaction (TX) / data confirmation
by a large number of coming and going nodes
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Problems of public blockchains• Transaction confirmation latency
– Block generation interval: 10 min in Bitcoin, 15 sec in Ethereum
• Transaction confirmation throughput– 7 TX/sec in Bitcoin, ‐300 TX/sec (est.) in Ethereum– 350 TX/sec in PayPal, 1,700 TX/sec in Visa– So‐called scalability problem ➡ second layer, …
• Total amount of data it stores– All the nodes store the identical data, > 200 GB– Does not scale along # of nodes➡ Downsampling [Li 2019], Distributing with DHT [Abe 2018], …
• Necessity of cryptocurrency operation– If the supporting cryptocurrency loses its economic value, nodes run
out, the blockchain cannot confirm TXs safely.➡ Portability and migration [Shudo 2018], …
• Number of other interesting problems
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Conflict betweenthroughput and security• Throughput improvement techniques result in decreased security.
Block propagation delay↑
Parameter
Ratio of these two determines throughput and security.
Parameter
Result
Result
Our goal is
Figures are from “Secure High-Rate Transaction Processing in Bitcoin”, FC’15, 2015
– Forks disperse the total confirming (hash) power to multiple tails of the blockchain.
– It facilitates 51% attack.
An example of highly forked blockchain.
decreasing block propagation delay
E.g. In Bitcoin,1 MB and 10 min result in 7 TPS.
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Towards coexistence ofperformance and security
• Propagation delay estimation with network coordinates
• Blockchain simulator
• Neighbor selection
• Measurement of relay networks
Relaynetworks
Blockchainsimulator
Neighbor selection
Measurement of relay
networks
Propagation delay estimation w/
network coordinates
Improvement ofTX confirmationthroughput
Improvement or preservation of security
Reduction of propagation time
CompactBlock Relay
Increase and adjustment ofblock gen. rate
[青木2019c][Aoki2019d]
[神田 2019a] [Kanda 2019b]
[青木 2019a] [Aoki 2019b] [Banno 2019]
[大月 2019a][Otsuki 2019b]
bloXroute, FIBRE, …
The following slides introducethese activities in order.
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Propagation delay estimation with network coordinates• Network coordinates [Dabek 2004] [Chen 2007]
– is applied to estimated block propagation delay.– Determine the coordinates in n‐dimensional Euclid space
using a physical mass‐spring system.
[神田 2019a][Kanda 2019b]
around 10,000 nodes
in msec
Brazil ?
• But …
• Purpose: A guide for– delay reduction techniques
– neighbor selection
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Propagation delay estimation with network coordinates• The accuracy is so so.
[神田 2019a][Kanda 2019b]
better
It is not ineffective.
Mean Square ErrorVivaldiAssumptions :degree 10,size of first hop group 15
Measured and estimated delays does not match well ?
In case just using the average
• Lack of topology information is the main obstacle.– cf. “TxProbe: Discovering Bitcoin’s Network Topology …”, FC’19, 2019
Measured de
lay (m
sec)
Estimated delay (msec)
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Simulator• A public blockchain “network” simulator
– developed by Distributed Systems Group, Tokyo Tech, and– released in June 2019.
• It simulates transmission of blocks between nodes over Internet, and PoW mining timein an event‐driven style. It will provides a visualizer.
• It simulates Bitcoin, Litecoin and Dogecoin.• Researches :
010002000
3000400050006000
700080009000
10000
0% 1% 5% 10% 50%
Med
ian bloc
k prop
agation time (m
sec)
Participation ratio
All nodes
Non‐participating nodes
Participating node
010002000
3000400050006000
700080009000
10000
0% 1% 5% 10% 50%
Med
ian bloc
k prop
agation time (m
sec)
Participation ratio
All nodes
Non‐participating nodes
Participating node
7400
7900
8400
8900
9400
0 2000 4000 6000 8000 10000
Med
ian bloc
k prop
agation time (m
sec)
The number of blocks
Normal Bitcoin algorithm
Proposed algorithm
7400
7900
8400
8900
9400
0 2000 4000 6000 8000 10000
Med
ian bloc
k prop
agation time (m
sec)
The number of blocks
Normal Bitcoin algorithm
Proposed algorithm
Neighbor selection Measurement of relay networks
[大月 2019a][Otsuki 2019b] [青木 2019c] [Aoki 2019d]
[青木 2019a] [Aoki 2019b] [Banno 2019]
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Simulator
Visualizer
Demoat IEEE ICBC 2019in Seoul
Web site
Bitcoin network,scaled down to 600 nodes for demo
[青木 2019a] [Aoki 2019b] [Banno 2019]
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Article on IEEE Spectrum
Proximity Neighbor Selection• Each node selects faster nodes as its neighbors.
– A major technique in the peer‐to‐peer field.E.g. Our trial for PNS in DHT [ISCC’13].
• Technique– Each node scores all the nodes that delivered a block to it.• score = time‐weighted average of(delivery_time – generation_time) of every blocks
– A node reselects its neighbors per 10 blocks.• But the node selects K nodes randomly from all the nodes it knows. Otherwise, a node has no distant neighbors and a block does not go far.
• K = 1, and P (the weight of the last propagation time) = 0.3based on a preliminary experiment
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[青木 2019c] [Aoki 2019d]
Proximity Neighbor Selection• Reduced from 11.5 sec to 8.5 sec
for slowly propagated blocks.
0%1%2%3%4%5%6%
45%50%
0 7000 8000 9000 10000 11000 12000 13000
提案⽅式
隣接ノード固定
Proposed technique
Fixed neighbors
Median block propagation time (msec)better
Reduced
[青木 2019c] [Aoki 2019d]
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Measurement of relay networks• Relay networks
– Fast block propagation networks– bloXroute (2018), FIBRE (2016), Falcon (2016), BFRN (2014), …– bloXroute: A business started by Cornell U. guys who have been working on Falcon
[大月 2019a] [Otsuki 2019b]
A relay network
An usualblockchain network
• Effect ?– How much does it reduce orphan blocks ?– Does it improve mining success rate ?
(Because a node using a relay network receives blocks earlier.)
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• SimBlock simulates a very fast relay network in addition to a Bitcoin network.
• Network‐level :
Measurement of relay networks
better
Faster propagation ! Reduced orphan blocks!Blocks outside the main chaincaused by forks• So, how about node‐level ?
better
[大月 2019a] [Otsuki 2019b]
Utilization rate Utilization rate
Utilizing nodesNon‐utilizing nodes
Orpha
n block rate
Mean block prop
agation de
lay (m
sec)
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• Node‐level :
Measurement of relay networks
bette
r
better
Mining success rate did not change …
Reduced probability that a block a utilizing node generated becomes an orphan block !➡Mining income increased.
A relay network certainly benefits a miner.
[大月 2019a] [Otsuki 2019b]
Non‐utilizing nodes
Utilizing nodes
Orpha
n block rate
Non‐utilizing nodes
Utilizing nodes
Average # of
succeede
d mining
Utilization rate Utilization rate
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Researches onblockchain “network”
• Problems:Transaction confirmation– delay– throughput
• Various trials as the figure on the right
• Acknowledgments– This work was supported by
SECOM Science and Technology Foundation.
– The work on delay estimation was supported by Kaula, Inc.
Relaynetworks
Blockchainsimulator
Neighbor selection
Measurement of relay
networks
Propagation delay estimation w/
network coordinates
Improvement ofTX confirmationthroughput
Improvement or preservation of security
Reduction of propagation time
CompactBlock Relay
Increase and adjustment ofblock gen. rate
[青木2019c][Aoki2019d]
[神田 2019a] [Kanda 2019b]
[青木 2019a] [Aoki 2019b] [Banno 2019]
[大月 2019a][Otsuki 2019b]
bloXroute, FIBRE, …
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Papers• Our papers
– [Shudo 2018] “Towards Application Portability on Blockchains“, IEEE HotICN 2018, August 2018– [神田 2019a] “ビットコインネットワーク上でのデータ伝搬遅延推定”, 信学技報, Vol.118, No.481, IA2018‐77, pp.317‐
322, March 2019– [Kanda 2019b] “Estimation of Data Propagation Time on the Bitcoin Network”, AINTEC 2019, August 2019– [大月 2019a] “Bitcoinネットワークに対するリレーネットワークの影響”, 信学技報, Vol.118, No.481, IA2018‐76, pp.309‐
316, March 2019– [Otsuki 2019b] “Effects of a Simple Relay Network on the Bitcoin Network”, AINTEC 2019, 2019年 8月– [青木 2019a] “SimBlock: ブロックチェーンネットワークシミュレータ”, 信学技報, Vol.118, No.481, IA2018‐70, pp.219‐
224, March 2019– [Aoki 2019b] “SimBlock: A Blockchain Network Simulator“, CryBlock 2019, April 2019– [Banno 2019] “Simulating a Blockchain Network with SimBlock“, IEEE ICBC 2019, pp.3‐4, May 2019– [青木 2019c] “ブロックチェーンネットワークにおける隣接ノード選択”, 信学技報, Vol.118, No.481, IA2018‐71, pp.225‐
232, March 2019– [Aoki 2019d] “Proximity Neighbor Selection in Blockchain Networks“, IEEE Blockchain 2019, July 2019– [Miyao 2013] “A Method for Designing Proximity‐aware Routing Algorithms for Structured Overlays”, IEEE ISCC’13,
July 2013
• Papers by others– [Li 2019] “Downsampling Blockchain Algorithm”, CryBlock 2019, April 2019– [Abe 2018] “Mitigating Bitcoin Node Storage Size By DHT”, AINTEC 2018, November 2018– “Secure High‐Rate Transaction Processing in Bitcoin”, FC’15, January 2015– [Dabek 2004] “Vivaldi: A Decentralized Network Coordinate System”, ACM SIGCOMM 2004, September 2004– [Chen 2007] “Pharos: A Decentralized and Hierarchical Network Coordinate System for Internet Distance Prediction”,
IEEE GLOBECOM 2007, December 2007– “TxProbe: Discovering Bitcoin’s Network Topology Using Orphan Transactions”, FC’19, February 2019
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