BeSelfishandAvoidDilemmas

ForkAfterWithholdingAttacksonBitcoin

Y.Kwon,D.Kim,Y.Son,E.Vasserman,Y.Kim.CCS2017.

SimonBienz

Blockchain

Image:https://d2omlh28jsv4r7.cloudfront.net/wp-content/uploads/2016/09/image-4-276x300.png

Blockchain:Mining

Reward

MiningPools

Blockchain:Fork

Bitcoin

• Digitalcurrency

• Completelypeer-to-peer

• Transactionsverifiedbynodes

• Underlyingblockchain actsasledger

• Coinscreatedbymining

Image:https://bitcoin.org/img/icons/opengraph.png

Bitcoin:Block

Header:Merkle rootofdata+hash(previousheader)+Nonce

Data:Transactions

Header

Data

Header

Data

SelfishMining

CreateForkintentionally

private

public

SelfishMining:Reward

MajorityIsNotEnough:BitcoinMiningIsVulnerable;Ittay Eyal andEmin GunSirer; 2014;

BlockWithholdingAttack

Lossfortheattackedpool

FPoW❌

PPoW✔

Image:https://www.buybitcoinworldwide.com/wp-content/uploads/2017/02/i1000-_0000_Vector-Smart-Object-300x300.png

BlockWithholdingAttack

Lossforpool+rewardforattacker

FPoW

Image:https://www.buybitcoinworldwide.com/wp-content/uploads/2017/02/i1000-_0000_Vector-Smart-Object-300x300.png

❌

BWH:Attacker’sDilemma

ForkAfterWithholdingAttack

+FPoW❌

PPoW✔

FAW:AttackingOnePool

FAW:AttackingOnePool

InnocentMiner

InfiltrationMiner

noimmediateFPoW propagation

FPoW holding+2nd Blockfound

1) mineroutside:

2) honestminer:

3) owninnocentminer:

FPoW❌

FPoW❌

RewardAttacker

…

…

…

…

attackerinnocentmining

honestminerinpool

otherminer

attackerinfiltration

otherminer

FAW BWH

RewardAttacker

1

0.8

0.6

0.4

0.2

000.10.20.30.40.5

4.5

3.5

2.5

1.5

0.5

PoolSize

c(coe

fficien

t)

ExtraRe

ward(%

)

RewardPool

…

…

…

…

attackerinnocentmining

honestminerinpool

otherminer

attackerinfiltration

otherminer

FAW NoAttack

PoolReward

1

0.8

0.6

0.4

0.2

000.10.20.30.40.5

0

-2

-6

-8

-10

-12

PoolSize

c(coe

fficien

t)

ExtraRe

ward(%

)

FAW:AgainstMultiplePools

FAW:AgainstMultiplePools

InnocentMiner

InfiltrationMiner

noimmediateFPoW propagation

FPoW holding+2nd Blockfound

1) mineroutside:

2) honestminer:

3) owninnocentminer:

FPoW❌

FPoW❌

RewardAttackerattackerinnocentmining

honestminerinpool

otherminer

attackerinfiltration

otherminer

FAW BWH

……

…

… attackerinfiltrationpool1

attackerinfiltrationpool2

RewardAttacker

FAW:AttackGame

AttackGame

Pool1InfiltrationPower Pool2InfiltrationPower

AttackGame

NetworkCapability

PoolSize1

PoolSize

2

PoolSize1

PoolSize

2

FAWvsSelfishMining

1

0.8

0.6

0.4

0.2

000.10.20.30.40.5

4.5

3.5

2.5

1.5

0.5

PoolSize

c(coe

fficien

t)

ExtraRe

ward(%

)

RationalManager

localFPoW

otherminersblock

?

DetectingAttacks

vs

FAW:Countermeasures

• TwophaseprotocolEyal,Rosenfeld

• beacon

• honeypotEyal

• joiningfeeEyal,Luu etal.

• bonus

Conclusions

• rewardlowerboundedbyBWH• rathersmallgaincomparedtoselfishmining• gainpossiblesingleminer/smallpools• noattackersdilemma• attackhardertodetect