Bitcoins Lightning Network: A Closer Look Blockchains HUJI 2021-05-06 | The Lightning Network is considered to be Bitcoin's greatest hope of scaling up the number of transactions that can be done with the currency. This is a recording of a talk at BGU explaining the principles underlying the operation of this network and discussing several vulnerabilities that we explored in our research.
FC Sliding Window Challenge Process for Congestion Detection Blockchains HUJI 2022-04-15 | How to automatically extend deadlines on the blockchain.Talk by Ayelet Lotem presented at Financial Cryptography and Data Security 2022 on a paper titled "Sliding Window Challenge Process for Congestion Detection" by Ayelet Lotem, Sarah Azouvi, Patrick McCorry, and Aviv Zohar. The paper is online at arxiv.org/pdf/2201.09009.pdfPost in Medium: https://t.co/g6SA3b8RDk
5 Minutes on Congestion Attacks in Payment Channel Networks Blockchains HUJI 2021-03-04 | 5-Minute talk by Ayelet Lotem (Mizrahi) presented at Financial Cryptography and Data Security 2021.Full video version (30 minutes): youtu.be/mTWRpNZqpzUThe paper is online at arxiv.org/pdf/2002.06564.pdfPost in Medium: medium.com/blockchains-huji/congestion-attacks-in-payment-channel-networks-b7ac37208389tl;dr: Each Lightning channel has a finite number of payments that can be accessed through the channel at any time. An attacker can open many small payments at once and leave them unresolved for several days at a time. It is possible to disrupt the Lightning Network by locking most of its liquidity spending less than half a bitcoin.
Congestion Attacks in Payment Channel Networks Blockchains HUJI 2021-03-04 | Talk by Ayelet Lotem (Mizrahi) presented at Financial Cryptography and Data Security 2021 on a paper titled "Congestion Attacks in Payment Channel Networks" by Ayelet Mizrahi, Aviv Zohar. The paper is online at arxiv.org/pdf/2002.06564.pdfPost in Medium: medium.com/blockchains-huji/congestion-attacks-in-payment-channel-networks-b7ac37208389tl;dr: Each Lightning channel has a finite number of payments that can be accessed through the channel at any time. An attacker can open many small payments at once and leave them unresolved for several days at a time. It is possible to disrupt the Lightning Network by locking most of its liquidity spending less than half a bitcoin.
Hijacking Routes in Payment Channel Networks: A Predictability Tradeoff (ACM AFT 20) Blockchains HUJI 2021-03-04 | Our talk in ACM Advances in Financial Technologies 2020.Medium post: medium.com/blockchains-huji/route-hijacking-and-dos-in-off-chain-networks-37ce6f54aa26Full version can be found in: arxiv.org/pdf/1909.06890.pdfAbstract: Off-chain transaction networks can mitigate the scalability issues of today's trustless electronic cash systems such as Bitcoin. However, these peer-to-peer networks also introduce a new attack surface which is not well-understood today. This paper identifies and analyzes, a novel Denial-of-Service attack which is based on route hijacking, i.e., which exploits the way transactions are routed and executed along the created channels of the network. This attack is conceptually interesting as even a limited attacker that manipulates the topology through the creation of new channels can navigate tradeoffs related to the way it attacks the network. Furthermore, the attack also highlights a fundamental design tradeoff for the defender (who determines its own routes): to become less predictable and hence secure, a rational node has to pay higher fees to nodes that forward its payments. We find that the three most common implementations for payment channels in Bitcoin (lnd, C-lightning, Eclair) approach routing differently. We begin by surveying the current state of the Lightning network and explore the routes chosen by these implementations. We find that in the current network nearly 60\% of all routes pass through only five nodes, while 80\% go through only 10 nodes. Thus, a relatively small number of colluding nodes can deny service to a large fraction of the network. We then turn to study an external attacker who creates links to the network and draws more routes through its nodes by asking for lower fees. We find that just five new links are enough to draw the majority (65% - 75%) of the traffic regardless of the implementation being used. The cost of creating these links is very low. We discuss the differences between implementations and eventually derive our own suggested routing policy, which is based on a novel combination of existing approaches.
How to Pick Your Friends - A Game Theoretic Approach to P2P Overlay Construction (ACM AFT 20) Blockchains HUJI 2021-03-04 | Our talk in ACM Advances in Financial Technologies 2020.Full version can be found in: dl.acm.org/doi/pdf/10.1145/3419614.3423252Abstract: A major limitation of open P2P networks is the lack of strong identities. This allows any agent to attack the system by creating multiple false personas, thereby disrupting the overlay network's connectivity and sabotaging its operation. In this paper, we explore practical ways to defend P2P networks from such attacks. To do so, we employ a game theoretic approach to the management of each peer's list of known nodes and to the overlay construction mechanisms that utilize this list. We consider the interaction between defender and attacker agents as a zero-sum game. We show that the cost of attacks can be driven up substantially if the defender utilizes available information about peers it chooses to connect to, such as their IP address. In addition to theoretical analysis of the underlying game, we apply our approach to the Bitcoin P2P network and derive effective strategies that guarantee a high safety level against attacks.
