An Edge Colouring-based Collaborative Routing Protocol for Blockchain Offline Channels

A Path-based Fund Transfer (PBT) in blockchain offline channel networks or in credit networks, uses a path among the offline channels to transfer funds among the peers who do not have mutual channels. A routing algorithm for PBT finds a suitable path for PBT execution. The problems with the landmark-based routing algorithms for PBT executions are as follows: (1) PBTs through hubs may cause privacy problems as a few landmarks can collude to find the sender and the receiver of a PBT, (2) Landmarks can be targeted with DoS or Eclipse attack. Unavailability of landmarks will lead to a high failure rate of PBT and (3) the unavailability of nodes for PBT execution creates cuts in the trees maintained by landmark-based routing protocols, which will lead to failure of PBT execution. In this paper, we mitigate the above problems with routing algorithms for PBT execution with a graph edge colouring-based routing protocol. In this routing protocol, every peer maintains a set of small subgraphs of the channel network with a particular topology. The peers exchange such subgraph information to find an appropriate path for PBT execution. Our contributions are as follows: (1) We develop a distributed algorithm to find subgraphs maintained by a peer. We prove that despite sharing subgraph information, our protocol preserves the privacy of the sender and the receiver of a PBT. (2) We prove that the proposed protocol is secure against adversarial peers initially agrees to participate in PBT execution and included in the trees or subgraphs computed by landmark-based or our edge colour-based routing algorithm, but later they do not participate in PBT execution. (3) We show that trees built by landmark-based algorithms require more frequent rebuilding as values in individual channels are changed over time compared with subgraphs to be maintained by the peers. (4) We show that the success rate and time to execute PBT for the proposed edge colouring-based routing algorithm is competitive against the landmark-based routing algorithm. (5) We show that DoS attacks resulting unavailability of peers have less impact on the proposed routing algorithm compared with landmark-based routing algorithms.