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

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

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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

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SybilQuorum: Open Distributed Ledgers through Trust Networks

Authors Alberto Sonnino* George Danezis*

and chainspace.io

January 2019

* University College London

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The Authors

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George Danezis Alberto Sonnino

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Many challenges in blockchains

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send it to the blockchain anyone can verify write the contract

Poor privacy Scalability Security Governance

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Many challenges in blockchains

Poor privacy Scalability Security Governance

Open systems need strong sybil defences

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Our focus: bootstrapping an FBAS

Nodes do not have to be known ahead of time

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Nodes choose whom they trust

Our focus: bootstrapping an FBAS

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How to achieve this with strong sybil resistance?

Our focus: bootstrapping an FBAS

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  • Attacker creates multiple fake identities

What are sybil attacks?

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  • Attacker creates multiple fake identities

… and takes over the system

What are sybil attacks?

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What should we do?

Cap the ability of the adversary to create multiple identities

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  • Traditional defences

Proof-of-Work Proof-of-Stake

What are sybil attacks?

$ $

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  • Traditional defences

Leverage scarce resources: Proof-of-Work Proof-of-Stake Money — by forcing to burn/lock it

What are sybil attacks?

$ $

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  • Traditional defences

What are sybil attacks?

extra money extra money extra money

The adversary needs to be rich

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  • Sometimes it is not enough…

Decentralised trading of financial products ( potentially worth $$$ )

What are sybil attacks?

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  • Sometimes it is not enough…
  • 1. borrow a lot of money
  • 2. turn it into tokens
  • 4. payback the bank
  • 3. subvert the system

exchange

What are sybil attacks?

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  • Can we strengthen existing mechanisms?

Leverage scare resources: Money — by forcing to burn/lock it

What are sybil attacks?

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What are sybil attacks?

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  • Can we strengthen existing mechanisms?

Leverage scare resources: Money — by forcing to burn/lock it Trust — by penalising poor judgements

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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. To defend against this, we use two-way stake wagers between entities, to build a social network of stake-weighted trust relationships. (Academic paper ‘Buffy’ coming soon)

We use social network theory to assess whether an entity is a sybil Poorly connected nodes to the main network see their stake attenuated.

4 OPEN SYSTEM WITH PROOF OF STAKE

How do we make that happen?

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Proof of Stake Social network analysis

SybilQuorum

Lock stake on particular social links Statistical analysis of nodes relationships

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. To defend against this, we use two-way stake wagers between entities, to build a social network of stake-weighted trust relationships. (Academic paper ‘Buffy’ coming soon)

We use social network theory to assess whether an entity is a sybil Poorly connected nodes to the main network see their stake attenuated.

4 OPEN SYSTEM WITH PROOF OF STAKE

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How to bootstrap an FBAS?

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Attribute weights to people you trust Step 1

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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. To defend against this, we use two-way stake wagers between entities, to build a social network of stake-weighted trust relationships. (Academic paper ‘Buffy’ coming soon)

We use social network theory to assess whether an entity is a sybil Poorly connected nodes to the main network see their stake attenuated.

4 OPEN SYSTEM WITH PROOF OF STAKE

SybilQuorum: Step 1

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  • Stake-weighted trust relationships
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  • Stake-weighted trust relationships

Put money on links!

Both vertices can withdraw the money on the link

SybilQuorum: Step 1

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  • Stake-weighted trust relationships

Fraudsters can take the money and disappear Poor judgement is penalised

SybilQuorum: Step 1

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  • Stake-weighted trust relationships

Bulk dishonesty protects against strategic dishonesty

SybilQuorum: Step 1

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How to bootstrap an FBAS?

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Attribute weights to people you trust Step 1 Run social network analysis Step 2

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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. To defend against this, we use two-way stake wagers between entities, to build a social network of stake-weighted trust relationships. (Academic paper ‘Buffy’ coming soon)

We use social network theory to assess whether an entity is a sybil Poorly connected nodes to the main network see their stake attenuated.

4 OPEN SYSTEM WITH PROOF OF STAKE

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  • Fast mixing assumption

SybilQuorum: Step 2

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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. To defend against this, we use two-way stake wagers between entities, to build a social network of stake-weighted trust relationships. (Academic paper ‘Buffy’ coming soon)

We use social network theory to assess whether an entity is a sybil Poorly connected nodes to the main network see their stake attenuated.

4 OPEN SYSTEM WITH PROOF OF STAKE

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  • 1. Fast integration of

nodes into the network

  • Fast mixing assumption

SybilQuorum: Step 2

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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. To defend against this, we use two-way stake wagers between entities, to build a social network of stake-weighted trust relationships. (Academic paper ‘Buffy’ coming soon)

We use social network theory to assess whether an entity is a sybil Poorly connected nodes to the main network see their stake attenuated.

4 OPEN SYSTEM WITH PROOF OF STAKE

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  • 1. Fast integration of

nodes into the network

  • 2. Slow integration of

sybils into the network

  • Fast mixing assumption

SybilQuorum: Step 2

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  • Each node performs a local judgement

Node’s view of the network

SybilQuorum: Step 2

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  • Each node performs a local judgement

Black Box

Node’s view of the network

SybilQuorum: Step 2

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  • Each node performs a local judgement

Black Box

Node’s view of the network Map nodes to weights

1/3 1/8

…

SybilQuorum: Step 2

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= SybilInfer, SybilGuard, SybilLimit, …

  • Each node performs a local judgement

Black Box

Node’s view of the network

Black Box

Map pk to weights

1/3 1/8

…

SybilQuorum: Step 2

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How to bootstrap an FBAS?

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Attribute weights to people you trust Step 1 Determine the quorum slices Step 3 Run social network analysis Step 2

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SybilQuorum: Step 3

  • Specify quorum slice for each node

> y

H

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SybilQuorum: Step 3

  • Specify quorum slice for each node

> y all subsets > 2/3 |H|

H

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SybilQuorum: Step 3

  • Specify quorum slice for each node

> y all subsets > 2/3 |H|

H

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How to bootstrap an FBAS?

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Attribute weights to people you trust Step 1 Determine the quorum slices Step 3 Run social network analysis Step 2

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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. To defend against this, we use two-way stake wagers between entities, to build a social network of stake-weighted trust relationships. (Academic paper ‘Buffy’ coming soon)

We use social network theory to assess whether an entity is a sybil Poorly connected nodes to the main network see their stake attenuated.

4 OPEN SYSTEM WITH PROOF OF STAKE

Experimental evaluation

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  • 1. Number of sybil nodes?
  • 2. Number of links/stake

between sybils?

  • 3. Number of links/stake

between nodes and sybils?

  • 4. Fraction of naïve nodes?
  • What to evaluate?
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Conclusion

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SybilQuorum: Sybil resistance mechanism

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Conclusion

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  • What?

Leverage Money by forcing to burn/lock it Leverage Trust by penalising poor judgement

SybilQuorum: Sybil resistance mechanism

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Conclusion

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  • What?
  • How?

Proof-of-Stake: build a stake-weighted graph Social network analysis: determine sybil regions Leverage Money by forcing to burn/lock it Leverage Trust by penalising poor judgement

SybilQuorum: Sybil resistance mechanism

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This work is supported in part by EPSRC Grant EP/M013286/1, the EU H2020 DECODE project (grant agreement number 732546), and chainspace.io

Alberto Sonnino http://sonnino.com

Thank you for your attention Questions?