Congestion Attacks in Payment Channel Networks

Ayelet Mizrahi*, Aviv Zohar

*Corresponding author for this work

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

22 Scopus citations


Payment channel networks provide a fast and scalable solution to relay funds, acting as a second layer to slower and less scalable blockchain protocols. In this paper, we present an accessible, low-cost attack in which the attacker paralyzes multiple payment network channels for several days. The attack is based on overloading channels with requests that are kept unresolved until their expiration time. Reaching the maximum allowed unresolved requests (HTLCs ) locks the channel for new payments. The attack is in fact inherent to the way off-chain networks are constructed, since limits on the number of unresolved payments are derived from limits on the blockchain. We consider three versions of the attack: one in which the attacker attempts to block as many high liquidity channels as possible, one in which it disconnects as many pairs of nodes as it can, and one in which it tries to isolate individual nodes from the network. We evaluate the costs of these attacks on Bitcoin’s Lightning Network and compare how changes in the network have affected the cost of attack. Specifically, we consider how recent changes to default parameters in each of the main Lightning implementations contribute to the attacks. Finally, we suggest mitigation techniques that make these attacks much harder to carry out.

Original languageAmerican English
Title of host publicationFinancial Cryptography and Data Security - 25th International Conference, FC 2021, Revised Selected Papers
EditorsNikita Borisov, Claudia Diaz
PublisherSpringer Science and Business Media Deutschland GmbH
Number of pages19
ISBN (Print)9783662643303
StatePublished - 2021
Event25th International Conference on Financial Cryptography and Data Security, FC 2021 - Virtual, Online
Duration: 1 Mar 20215 Mar 2021

Publication series

NameLecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)
Volume12675 LNCS
ISSN (Print)0302-9743
ISSN (Electronic)1611-3349


Conference25th International Conference on Financial Cryptography and Data Security, FC 2021
CityVirtual, Online

Bibliographical note

Publisher Copyright:
© 2021, International Financial Cryptography Association.


  • HTLC
  • Lightning Network
  • Network security
  • Payment channel networks


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