  We propose and experimentally evaluate a novel secure aggregation algorithm
targeted at cross-organizational federated learning applications with a fixed
set of participating learners. Our solution organizes learners in a chain and
encrypts all traffic to reduce the controller of the aggregation to a mere
message broker. We show that our algorithm scales better and is less resource
demanding than existing solutions, while being easy to implement on constrained
platforms.
  With 36 nodes our method outperforms state-of-the-art secure aggregation by
70x, and 56x with and without failover, respectively.
