Randomness certification is a foundational and practical aspect of quantum information science, essential for se-curing quantum communication protocols. Traditionally, these protocols have been implemented and validatedwith a single entanglement source, as in the paradigmatic Bell scenario. However, advancing these protocols tosupport more complex configurations involving multiple entanglement sources is key to building robust architec-tures and realizing large-scale quantum networks. Here, we show how to certify randomness in an entanglement-teleportation experiment, the building block of a quantum repeater displaying two independent sources ofentanglement. Using the scalar extension method, we address the challenge posed by the nonconvexity of thecorrelation set, providing effective bounds on an eavesdropper’s knowledge of the shared secret bits. Our theo-retical model characterizes the certifiable randomness within the network and is validated through the analysis ofexperimental data from a photonic quantum network.
