@ -43,7 +43,7 @@ In all cases, some privacy of the payer and the recipient are lost.
[[malicious-routing-diagram]]
.If the Malicious node knows there are 2 layers left, then it knows that the payment recipient is either Node 19 (and there were only 19 hops) or one of Node 19's channel partners
image:images/malicious-routing-diagram.png["If the Malicious node knows there are 2 layers left, then it knows that the payment recipient is either Node 19 (and there were only 19 hops) or one Node 19's channel partners"]
image:images/malicious-routing-diagram.PNG["If the Malicious node knows there are 2 layers left, then it knows that the payment recipient is either Node 19 (and there were only 19 hops) or one Node 19's channel partners"]
We can extend this example.
Imagine a malicious entity sets up multiple Lightning nodes connected to other well-connected nodes, and it also connects itself across popular payment routes.
* How can the flexible onion space be used to enabled packet switching in the network?
==== Finding a path
Payments on the Lightning Network are forwarded along a path of channels from one participant to another.
Thus, a path of payment channels has to be selected.
If we knew the exact channel balances of every channel we could easily compute a payment path using any of the standard path finding algorithms taught in any computer science program.
This could even be done in a way to optimize the fees that would have to be paid by the payer to the nodes that kindly forward the payment.
However, as discussed the balance information of all channels is and cannot be available to all participants of the network.
Thus, we need to have one or more innovative path finding strategy.
These strategies must relate closely to the routing algorithm that is used.
As we will see in the next section, the Lightning Network uses a source based onion routing protocol for routing payments.
This means in particular that the sender of the payment has to find a path through the network.
With only partial information about the network topology available this is a real challenge and active research is still being conducted into optimizing this part of the Lightning Network implementations.
The fact that the path finding problem is not fully solved for the case of the Lightning Network is a major point of criticism towards the technology.
The path finding strategy currently implemented in Lightning nodes is to probe paths until one is found that has enough liquidity to forward the payment.
While this is not optimal and certainly can be improved, it should be noted that even this simplistic strategy works well.
This probing is done by the Lightning node or wallet and is not directly seen by the user of the software.
The user might only realize that probing is taking place if the payment is not going through instantly.
The algorithm currently also does not necessarily result in the path with the lowest fees.
=======
=== What is "Source-Based" routing and why does the Lightning Network use it?
Source-based routing is a method of path-finding where the sender (i.e. the source) plans the route from itself, through the intermediary nodes, and finally to the destination.
Rene Pickhardt
4 years ago