Publications

2024

1. AFT

   Payment Censorship in the Lightning Network Despite Encrypted Communication

   Charmaine Ndolo, and Florian Tschorsch

   In 6th Conference on Advances in Financial Technologies (AFT 2024), 2024

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   The Lightning network (LN) offers a solution to Bitcoin’s scalability limitations by providing fast and private off-chain payments. In addition to the LN’s long known application-level centralisation, recent work has highlighted its centralisation at the network-level which makes it vulnerable to attacks on privacy by malicious actors. In this work, we explore the LN’s susceptibility to censorship by a network-level actor such as a malicious autonomous system. We show that a network-level actor can identify and censor all payments routed via their network by just examining the packet headers. Our results indicate that it is viable to accurately identify LN messages despite the fact that all inter-peer communication is end-to-end encrypted. Additionally, we describe how a network-level observer can determine a node’s role in a payment path based on timing, direction of flow and message type, and demonstrate the approach’s feasibility using experiments in a live instance of the network. Simulations of the attack on a snapshot of the Lightning mainnet suggest that the impact of the attack varies from mild to potentially dramatic depending on the adversary and type of payments that are censored. We analyse countermeasures the network can implement and come to the conclusion that an adequate solution comprises constant message sizes as well as dummy traffic.

   @inproceedings{ndolo2024payment,
     author = {Ndolo, Charmaine and Tschorsch, Florian},
     title = {{Payment Censorship in the Lightning Network Despite Encrypted Communication}},
     booktitle = {6th Conference on Advances in Financial Technologies (AFT 2024)},
     pages = {12:1--12:24},
     series = {Leibniz International Proceedings in Informatics (LIPIcs)},
     isbn = {978-3-95977-345-4},
     issn = {1868-8969},
     year = {2024},
     volume = {316},
     publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
     url = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.AFT.2024.12},
     doi = {10.4230/LIPIcs.AFT.2024.12},
   }

2023

1. CBT

   On the (Not So) Surprising Impact of Multi-Path Payments on Performance And Privacy in the Lightning Network

   Charmaine Ndolo, and Florian Tschorsch

   In Computer Security. ESORICS 2023 International Workshops - CyberICS, DPM, CBT, and SECPRE, The Hague, The Netherlands, September 25-29, 2023, Revised Selected Papers, Part I, 2023

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   The Lightning network (LN) addresses Bitcoin’s scalability issues by providing fast and private payment processing. In order to mitigate failures caused by insufficient channel capacities, LN introduced multi-path payments. To the best of our knowledge, the effect of multi-path payments remains unclear. In this paper, we therefore study the impact of multi-path payments on performance and privacy. We identify metrics quantifying the aforementioned properties and utilise them to evaluate the impact of multi-path payments. To this end, we develop a simulator implementing pathfinding in LN using single and multi-path payments as well as various pathfinding algorithms. We find that, while the success rate of multi-path payments is up to 20% higher, the impact of multi-path payments on performance otherwise remains within limits. On the other hand, the impact on privacy appears to be greater, e.g., multi-path payments are more likely to encounter an on-path adversary and the relationship anonymity is more likely to be compromised by colluding intermediate hops. However, multi-path payments are less likely to be deanonymised based on the path lengths.

   @inproceedings{ndolo2023on,
     author = {Ndolo, Charmaine and Tschorsch, Florian},
     title = {On the (Not So) Surprising Impact of Multi-Path Payments on Performance
                         And Privacy in the Lightning Network},
     booktitle = {Computer Security. {ESORICS} 2023 International Workshops - CyberICS,
                         DPM, CBT, and SECPRE, The Hague, The Netherlands, September 25-29,
                         2023, Revised Selected Papers, Part {I}},
     series = {Lecture Notes in Computer Science},
     volume = {14398},
     pages = {411--427},
     publisher = {Springer},
     year = {2023},
     doi = {10.1007/978-3-031-54204-6\_25},
   }

2. BRAINS

   Fair Reward Distribution in Federated Byzantine Agreement Systems

   Charmaine Ndolo, Martin Florian, and Florian Tschorsch

   In 5th Conference on Blockchain Research & Applications for Innovative Networks and Services, BRAINS 2023, Paris, France, October 11-13, 2023, 2023

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   Federated Byzantine Agreement Systems (FBASs) offer a solution to consensus in permissionless systems by adapting the well-studied Byzantine agreement model to permissionless consensus. Unlike its counterparts in the context of permissionless consensus, the FBAS system model does not offer validating nodes protocol-level incentives although they are entrusted with safeguarding and ensuring the functionality of the system. Multiple studies have reported on the small number of active validators in these systems leading to some concerns about their resilience. To this end, this paper studies how rewards can be distributed in FBASs and presents a fair reward distribution function for FBASs. The challenge is that, on the one hand, consensus in an FBAS is found jointly between all nodes and, on the other hand, nodes do not all contribute equally to this process. We draw on game-theoretic methods to quantify these contributions bearing the overall health of the FBAS in mind and present a fair reward distribution function which we evaluate based on a set of identified properties.

   @inproceedings{ndolo2023fair,
     author = {Ndolo, Charmaine and Florian, Martin and Tschorsch, Florian},
     title = {{Fair Reward Distribution in Federated Byzantine Agreement Systems}},
     booktitle = {5th Conference on Blockchain Research {\&} Applications for Innovative
                         Networks and Services, {BRAINS} 2023, Paris, France, October 11-13,
                         2023},
     pages = {1--8},
     publisher = {{IEEE}},
     year = {2023},
     doi = {10.1109/BRAINS59668.2023.10316929},
   }

2022

1. DC

   The Sum of Its Parts: Analysis of Federated Byzantine Agreement Systems

   Martin Florian, Sebastian Henningsen, Charmaine Ndolo, and 1 more author

   Distributed Computing, 2022

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   Federated Byzantine Agreement Systems (FBASs) are a fascinating new paradigm in the context of consensus protocols. Originally proposed for powering the Stellar payment network, FBASs can instantiate Byzantine quorum systems without requiring out-of-band agreement on a common set of validators; every node is free to decide for itself with whom it requires agreement. Sybil-resistant and yet energy-efficient consensus protocols can therefore be built upon FBASs, and the “decentrality” possible with the FBAS paradigm might be sufficient to reduce the use of environmentally unsustainable proof-of-work protocols. In this paper, we first demonstrate how the robustness of individual FBASs can be determined, by precisely determining their safety and liveness buffers and therefore enabling a comparison with threshold-based quorum systems. Using simulations and example node configuration strategies, we then empirically investigate the hypothesis that while FBASs can be bootstrapped in a bottom-up fashion from individual preferences, strategic considerations should additionally be applied by node operators in order to arrive at FBASs that are robust and amenable to monitoring. Finally, we investigate the reported “open-membership” property of FBASs. We observe that an often small group of nodes is exclusively relevant for determining liveness buffers and prove that membership in this top tier is conditional on the approval by current top tier nodes if maintaining safety is a core requirement.

   @article{florian2022sum,
     title = {The Sum of Its Parts: Analysis of Federated Byzantine Agreement Systems},
     author = {Florian, Martin and Henningsen, Sebastian and Ndolo, Charmaine and Scheuermann, Björn},
     journal = {Distributed Computing},
     publisher = {Springer},
     doi = {10.1007/s00446-022-00430-0},
     year = {2022},
   }

2021

1. arXiv

   Crawling the MobileCoin Quorum System

   Charmaine Ndolo, Sebastian A. Henningsen, and Martin Florian

   2021

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   We continuously crawl the young MobileCoin network, uncovering the quorum configurations of core nodes and the quorum system resulting from these configurations. This report discusses our crawl methodology, encountered challenges, and our current empirical results. We find that the MobileCoin quorum system currently comprises of 7 organisations controlling a total of 10 validator nodes. Current quorum set configurations prioritise safety over liveness. At the time of writing, one of the involved organisations is technically able to block the approval of new blocks, as is the case for one of the (two) ISPs employed by crawled nodes.

   @misc{ndolo2021crawling,
     author = {Ndolo, Charmaine and Henningsen, Sebastian A. and Florian, Martin},
     title = {{Crawling the MobileCoin Quorum System}},
     year = {2021},
     url = {https://arxiv.org/abs/2111.12364},
   }