  One of the main open problems in quantum communication is the design of
efficient quantum-secured networks. This is a challenging goal, because it
requires protocols that guarantee both unconditional security and high
communication rates, while increasing the number of users. In this scenario,
continuous-variable systems provide an ideal platform where high rates can be
achieved by using off-the-shelf optical components. At the same time, the
measurement-device independent architecture is also appealing for its feature
of removing a substantial portion of practical weaknesses. Driven by these
ideas, here we introduce a modular design of continuous-variable network where
each individual module is a measurement-device-independent star network. In
each module, the users send modulated coherent states to an untrusted relay,
creating multipartite secret correlations via a generalized Bell detection.
Using one-time pad between different modules, the network users may share a
quantum-secure conference key over arbitrary distances at constant rate.
