Researchers discover that the Bitcoin Lightning Network could be vulnerable to attacks that can delay or completely stop payment channels. Although there is no way to know how dangerous this potential DoS attack is, it is considered a major flaw in the network.
Attack With an Amplified DoS
The research paper, that was written by Saar Tochner, Aviv Zohar, and Stefan Schmid, describes an amplified DoS attack that could easily slow down or even stop a huge percentage of the payment channels on the lightning network. This can be achieved because each payment in the lightning network is passed across nodes in order to get to its final destination. If one of these nodes is a “bad actor”, it can slow down the transaction, rather than passing it swiftly along.
It is considered very easy to execute currently but thankfully, such an attack is yet to be seen in the “wild”. As mentioned earlier, when a user sends a payment to the lightning network, their app decides which path to take based on a plethora of factors, including nodes that require the lowest fees. A malicious group of users can manipulate these factors and the fees in order for their nodes to be chosen as part of the “path” as frequently as possible. Thus, slowing down a majority of the payments being sent to the network (between 65% and 75%). This can be done over and over again, as there is a very high chance for another malicious node to be chosen as part of the path, when the first node denies the transaction.
Measures To Prevent The Attack
Although the developers of the Lightning network agreed that this is a serious threat, they remain confident that with future changes such attacks will become much more difficult to do. Like the infrastructure lead at Lightning Labs, Alex Bosworth, said “It’s something that’s hard to talk about because we are still developing the pathfinding system in LND and it’s a moving target.”.
The lightning code is changing at a rapid pace and plenty of modifications are still in the pipeline. Some of these updates will make it much harder for “bad actors” to execute an attack as well as the team doing their best to monitor for such malicious users and banning them. Also, in the future, there will be implementations that will aggressively target such users and the attacks will be short-lived, if they happen. Lightning startup Acinq CTO Fabrice Drouin stated that not only the cheapest fees are taken into consideration when choosing the nodes. Older channels are preferred, meaning a malicious user will need to behave and contribute to the network for some time before they can get picked.
Although the Lightning Network is supposed to be instant, behind the scenes the nodes in the network carry out payments from once place to the other and will need to do some computations. Not all lightning nodes actually have that computational power, for example when sending bitcoin from your smartphone. That’s why a system is in place, called the “trampoline” system. When a node cannot do the calculations by itself, it outsources the data to “trampoline” nodes that have the necessary resources.