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IEEE Tokyo Blockchain Workshop
July 29th, 2019

Researches on
Blockchain “Networks”
Kazuyuki Shudo
Tokyo Tech

首藤 一幸
東京工業大学Tokyo TechCryptocurrency anda public blockchain supporting it

1 / 15• A distributed system
supporting cryptocurrencies– Bitcoin’s market capitalization is
US$ 180B.
– Decentralized

A peer-to-peer(P2P) networkof participatingnodes• Expected applications= An application-levelnetwork

A hash chain of blocks
Block
Hash value

Hash value
TX

TX

A cryptographic
hash function

BlockTX

TX••

TXTX•

Node (miner)

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– Essentially, time stamp authority ornotary office– Supply chain mgmt., traceability,
governance process such as voting,automatic operation of organizations,…

9,200 nodes on Bitcoin networkhttps://bitnodes.earn.com/

Technologies
supporting blockchain

2 / 15What 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• Cryptography– Public‐key cryptography,
digital signature,
cryptographic hash function,
random number generation,…

• Distributed systems– Peer‐to‐peer networks,
flooding, replication,
consistency, consensus
algorithms, …

3 / 15

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 • Number of other– All the nodes store the identical data, > 200 GBinteresting problems– 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 runout, the blockchain cannot confirm TXs safely.
➡ Portability and migration [Shudo 2018], …

Conflict between
throughput and security

4 / 15• Throughput improvement techniques result
Result in decreased security.
E.g. In Bitcoin,– Forks disperse the total
confirming (hash) power toParameter
multiple tails of the blockchain.
– It facilitates 51% attack.
Block propagation
delay↑

1 MB and 10 min
result in 7 TPS.

Parameter

Ratio of thesetwo determines
throughput andsecurity.

Our goal isdecreasing block
Result propagation delay
An example of highly forked blockchain.
Figures are from “Secure High-Rate Transaction Processing in Bitcoin”, FCʼ15, 2015

5 / 15

Towards coexistence ofperformance and security• Propagation delay
estimation with
network coordinates• Blockchain
simulator• Neighbor selection• Measurement ofrelay networks

Improvement of

Improvement orpreservation of

TX confirmation
throughput
Increase andadjustment ofblock gen. ratesecurity

Reduction of
propagation time

Compact
Block Relay
bloXroute, FIBRE, …

Neighborselection[青木2019c][Aoki2019d]

Propagation delay
estimation w/
network coordinates[神田 2019a] [Kanda 2019b]

The following slides introduce
these activities in order.

Relaynetworks
Measurementof relay
networks[大月 2019a][Otsuki 2019b]

Blockchain
simulator[青木 2019a] [Aoki 2019b] [Banno 2019]6 / 15

Propagation delay estimation[神田 2019a]with network coordinates [Kanda 2019b]• 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.
around 10,000 nodes
Brazil ?

• Purpose: A guide for– delay reduction
techniques– neighbor selection

in msec• But …

7 / 15

Propagation delay estimation[神田 2019a]with network coordinates [Kanda 2019b]
VivaldiIn case just using the average
Mean Square Error

Assumptions :degree 10,size of first hop group 15

betterMeasured delay (msec)• The accuracy is so so.

Estimated delay (msec)

Measured and estimateddelays does not match well ?

It is not ineffective.

• Lack of topology information is the main obstacle.
– cf. “TxProbe: Discovering Bitcoin’s Network Topology …”, FC’19, 2019

8 / 15

Simulator[青木 2019a] [Aoki 2019b] [Banno 2019]• A public blockchain “network” simulator– developed by Distributed Systems Group, Tokyo Tech, and– released in June 2019.

• It simulates transmission of blocks between nodes overInternet, and PoW mining timein an event‐driven style. It will provides a visualizer.

Median block propagation time (msec)

Normal Bitcoin algorithm

9400

Proposed algorithm

8900

8400

7900

7400
0

2000

4000

6000

8000

10000

The number of blocks

Neighbor selection[青木 2019c] [Aoki 2019d]

Median block propagation time (msec)• It simulates Bitcoin, Litecoin and Dogecoin.
• Researches :
10000

9000

All nodes

8000

Non‐participating nodes

7000

Participating node

6000
5000
4000
3000
2000
1000
00%

1%

5%

10%

50%

Participation ratio

Measurement of [大月 2019a]
relay networks [Otsuki 2019b]

9 / 15

Simulator[青木 2019a] [Aoki 2019b] [Banno 2019]

Web site

Visualizer

Bitcoin network,
scaled down to 600 nodes for demo

Article onIEEESpectrum
Demo
at IEEE ICBC 2019in Seoul10 / 15

Proximity Neighbor Selection[青木 2019c] [Aoki 2019d]• 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 ablock 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) = 0.3
based on a preliminary experiment11 / 15

Proximity Neighbor Selection[青木 2019c] [Aoki 2019d]• Reduced from 11.5 sec to 8.5 sec
for slowly propagated blocks.
50%
45%
6%
5%
4%
3%
2%
1%
0%

提案⽅式
Proposed technique
隣接ノード固定
Fixed neighborsReduced07000 8000 9000 10000 11000 12000 13000
betterMedian block propagation time (msec)

12 / 15

Measurement of relay networks[大月 2019a] [Otsuki 2019b]• 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
A relay network

An usual• Effect ?

blockchain network– How much does it reduce orphan blocks ?
– Does it improve mining success rate ?
(Because a node using a relay network receives blocks earlier.)13 / 15

Measurement of relay networks

Non‐utilizingnodes

Utilizing nodes

Utilization rate

Faster propagation !

betterOrphan block rate

• SimBlock simulates a very fast relay network inaddition to a Bitcoin network.
• Network‐level :
betterMean block propagation delay (msec)[大月 2019a] [Otsuki 2019b]

Utilization rate

Reduced orphan blocks！

• So, how about node‐level ?

Blocks outside the main chaincaused by forks

14 / 15

Measurement of relay networks[大月 2019a] [Otsuki 2019b]• Node‐level :
betterMining success rate
did not change …

Non‐utilizing
nodes

Utilizing nodes

betterUtilization rate

Orphan block rate

Utilizing nodes

Average # ofsucceeded mining

Non‐utilizing
nodes

Utilization rate

Reduced probability that a blocka utilizing node generated
becomes an orphan block !
➡ Mining income increased.

A relay network certainly benefits a miner.

15 / 15

Researches onblockchain “network”• Problems:Transaction
confirmation– delay– throughput• Various trials as thefigure on the right• Acknowledgments– This work was supported by
SECOM Science andTechnology Foundation.
– The work on delay estimation
was supported by Kaula, Inc.

Improvement of

Improvement orpreservation of

TX confirmation
throughput
Increase andadjustment ofblock gen. ratesecurity

Reduction of
propagation time

Compact
Block Relay
bloXroute, FIBRE, …

Neighborselection[青木2019c][Aoki2019d]

Propagation delay
estimation w/
network coordinates[神田 2019a] [Kanda 2019b]

Relay
networks
Measurementof relay
networks[大月 2019a][Otsuki 2019b]

Blockchain
simulator[青木 2019a] [Aoki 2019b] [Banno 2019]References / 15

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