  Secret-sharing building blocks based on quantum broadcast communication are
studied. The confidential capacity region of the pure-loss bosonic broadcast
channel is determined, both with and without key assistance, and an achievable
region is established for the lossy bosonic broadcast channel. If the main
receiver has a transmissivity of \eta<1/2, then confidentiality solely relies
on the key-assisted encryption of the one-time pad. We also address conference
key agreement for the distillation of two keys, a public key and a secret key.
A regularized formula is derived for the key-agreement capacity region in
finite dimensions. In the bosonic case, the key-agreement region is included
within the capacity region of the corresponding broadcast channel with
confidential messages. We then consider a network with layered secrecy, where
three users with different security ranks communicate over the same broadcast
network. We derive an achievable layered-secrecy region for a pure-loss bosonic
channel that is formed by the concatenation of two beam splitters.
