  In the conventional left-right gauge model, if the Higgs scalar sector
consists only of an $SU(2)_L$ doublet and an $SU(2)_R$ doublet, fermion masses
are zero at tree level. There have been many studies on how they would become
massive. With the help of a dark sector with $U(1)_D$ gauge symmetry, it is
shown how all standard-model fermions may acquire realistic masses radiatively,
including that of the top quark. In this context, the particle content of the
model also implies the automatic conservation of baryon number $B$ and lepton
number $L$ as in the standard model. Observable anomalous Higgs couplings are
predicted.
