  We use simple currents to construct symmetric special Frobenius algebras in
modular tensor categories. We classify such simple current type algebras with
the help of abelian group cohomology. We show that they lead to the modular
invariant torus partition functions that have been studied by Kreuzer and
Schellekens. We also classify boundary conditions in the associated conformal
field theories and show that the boundary states are given by the formula
proposed in hep-th/0007174. Finally, we investigate conformal defects in these
theories.

High Energy Physics - Theory;Category Theory;Quantum Algebra