SybilQuorum: Open Distributed Ledgers through Trust Networks - PowerPoint PPT Presentation

SybilQuorum: Open Distributed Ledgers through Trust Networks Authors Alberto Sonnino * George Danezis * * University College London and chainspace.io January 2019

The Authors Alberto Sonnino George Danezis � 2

Many challenges in blockchains Poor privacy Scalability Governance Security send it to the blockchain write the contract anyone can verify � 3

Many challenges in blockchains Poor privacy Scalability Governance Security Open systems need strong sybil defences

Our focus: bootstrapping an FBAS Nodes do not have to be known ahead of time � 5

Our focus: bootstrapping an FBAS Nodes choose whom they trust � 6

Our focus: bootstrapping an FBAS How to achieve this with strong sybil resistance? � 7

What are sybil attacks? • Attacker creates multiple fake identities � 8

What are sybil attacks? • Attacker creates multiple fake identities … and takes over the system � 9

What should we do? Cap the ability of the adversary to create multiple identities � 10

What are sybil attacks? • Traditional defences Proof-of-Work Proof-of-Stake $ $ � 11

What are sybil attacks? • Traditional defences Proof-of-Work Proof-of-Stake $ $ Leverage scarce resources: Money — by forcing to burn/lock it � 12

What are sybil attacks? • Traditional defences extra money extra money The adversary needs to be rich extra money � 13

What are sybil attacks? • Sometimes it is not enough… Decentralised trading of financial products ( potentially worth $$$ ) � 14

What are sybil attacks? • Sometimes it is not enough… 2. turn it into tokens exchange 1. borrow a lot of money 3. subvert the system 4. payback the bank � 15

What are sybil attacks? • Can we strengthen existing mechanisms? Leverage scare resources: Money — by forcing to burn/lock it � 16

What are sybil attacks? • Can we strengthen existing mechanisms? Leverage scare resources: Money — by forcing to burn/lock it Trust — by penalising poor judgements � 17

How do we make that happen? SybilQuorum Social network analysis Proof of Stake 4 OPEN SYSTEM WITH PROOF OF STAKE 4 OPEN SYSTEM WITH PROOF OF STAKE An open system needs strong Sybil defences. An open system needs strong Sybil defences. Proof of Stake protocols: attackers can Proof of Stake protocols: attackers can simply borrow a lot of money, turn it into simply borrow a lot of money, turn it into tokens, and subvert the system. tokens, and subvert the system. Lock stake on particular Statistical analysis of We use social network theory to social links nodes relationships We use social network theory to To defend against this, we use two-way assess whether an entity is a sybil To defend against this, we use two-way stake wagers between entities, to build a assess whether an entity is a sybil social network of stake-weighted trust stake wagers between entities, to build a Poorly connected nodes to the main � 18 relationships . network see their stake attenuated. social network of stake-weighted trust Poorly connected nodes to the main (Academic paper ‘Buffy’ coming soon) relationships . network see their stake attenuated. (Academic paper ‘Buffy’ coming soon)

How to bootstrap an FBAS? Step 1 Attribute weights to people you trust � 19

SybilQuorum: Step 1 • Stake-weighted trust relationships 4 OPEN SYSTEM WITH PROOF OF STAKE An open system needs strong Sybil defences. Proof of Stake protocols: attackers can simply borrow a lot of money, turn it into tokens, and subvert the system. � 20 We use social network theory to To defend against this, we use two-way assess whether an entity is a sybil stake wagers between entities, to build a social network of stake-weighted trust Poorly connected nodes to the main relationships . network see their stake attenuated. (Academic paper ‘Buffy’ coming soon)

SybilQuorum: Step 1 • Stake-weighted trust relationships Put money on links! Both vertices can withdraw the money on the link � 21

SybilQuorum: Step 1 • Stake-weighted trust relationships Fraudsters can take the money and disappear Poor judgement is penalised � 22

SybilQuorum: Step 1 • Stake-weighted trust relationships Bulk dishonesty protects against strategic dishonesty � 23

How to bootstrap an FBAS? Step 1 Attribute weights to people you trust Step 2 Run social network analysis � 24

SybilQuorum: Step 2 • Fast mixing assumption 4 OPEN SYSTEM WITH PROOF OF STAKE An open system needs strong Sybil defences. Proof of Stake protocols: attackers can simply borrow a lot of money, turn it into tokens, and subvert the system. � 25 We use social network theory to To defend against this, we use two-way assess whether an entity is a sybil stake wagers between entities, to build a social network of stake-weighted trust Poorly connected nodes to the main relationships . network see their stake attenuated. (Academic paper ‘Buffy’ coming soon)

SybilQuorum: Step 2 • Fast mixing assumption 4 1. Fast integration of nodes into the network OPEN SYSTEM WITH PROOF OF STAKE An open system needs strong Sybil defences. Proof of Stake protocols: attackers can simply borrow a lot of money, turn it into tokens, and subvert the system. � 26 We use social network theory to To defend against this, we use two-way assess whether an entity is a sybil stake wagers between entities, to build a social network of stake-weighted trust Poorly connected nodes to the main relationships . network see their stake attenuated. (Academic paper ‘Buffy’ coming soon)

SybilQuorum: Step 2 • Fast mixing assumption 4 1. Fast integration of nodes into the network OPEN SYSTEM WITH PROOF OF STAKE 2. Slow integration of sybils into the network An open system needs strong Sybil defences. Proof of Stake protocols: attackers can simply borrow a lot of money, turn it into tokens, and subvert the system. � 27 We use social network theory to To defend against this, we use two-way assess whether an entity is a sybil stake wagers between entities, to build a social network of stake-weighted trust Poorly connected nodes to the main relationships . network see their stake attenuated. (Academic paper ‘Buffy’ coming soon)

SybilQuorum: Step 2 • Each node performs a local judgement Node’s view of the network � 28

SybilQuorum: Step 2 • Each node performs a local judgement Node’s view of the network Black Box � 29

SybilQuorum: Step 2 • Each node performs a local judgement Node’s view of the network 1/3 Black Box 1/8 … Map nodes to weights � 30

SybilQuorum: Step 2 • Each node performs a local judgement Node’s view of the network 1/3 Black Box 1/8 … Map pk to weights = SybilInfer, SybilGuard, SybilLimit, … Black Box � 31

How to bootstrap an FBAS? Step 1 Attribute weights to people you trust Step 2 Run social network analysis Step 3 Determine the quorum slices � 32

SybilQuorum: Step 3 • Specify quorum slice for each node > y H � 33

SybilQuorum: Step 3 • Specify quorum slice for each node > y H all subsets > 2/3 |H| � 34

SybilQuorum: Step 3 • Specify quorum slice for each node > y H all subsets > 2/3 |H| � 35

How to bootstrap an FBAS? Step 1 Attribute weights to people you trust Step 2 Run social network analysis Step 3 Determine the quorum slices � 36

Experimental evaluation • What to evaluate? 1. Number of sybil nodes? 4 3. Number of links/stake between nodes and sybils? OPEN SYSTEM WITH PROOF OF STAKE An open system needs strong Sybil 2. Number of links/stake defences. between sybils? Proof of Stake protocols: attackers can 4. Fraction of naïve nodes? simply borrow a lot of money, turn it into tokens, and subvert the system. We use social network theory to � 37 To defend against this, we use two-way assess whether an entity is a sybil stake wagers between entities, to build a social network of stake-weighted trust Poorly connected nodes to the main relationships . network see their stake attenuated. (Academic paper ‘Buffy’ coming soon)

Conclusion SybilQuorum: Sybil resistance mechanism � 38

Conclusion SybilQuorum: Sybil resistance mechanism • What? Leverage Money Leverage Trust by forcing to burn/lock it by penalising poor judgement � 39

Conclusion SybilQuorum: Sybil resistance mechanism • What? Leverage Money Leverage Trust by forcing to burn/lock it by penalising poor judgement • How? Social network analysis: Proof-of-Stake: determine sybil regions build a stake-weighted graph � 40

Thank you for your attention Questions? Alberto Sonnino http://sonnino.com This work is supported in part by EPSRC Grant EP/M013286/1, the EU H2020 DECODE project (grant agreement number 732546), and chainspace.io