  We consider entanglement through permeable interfaces in the c=1
(1+1)-dimensional conformal field theory. We compute the partition functions
with the interfaces inserted. By the replica trick, the entanglement entropy is
obtained analytically. The entropy scales logarithmically with respect to the
size of the system, similarly to the universal scaling of the ordinary
entanglement entropy in (1+1)-dimensional conformal field theory. Its
coefficient, however, is not constant but controlled by the permeability, the
dependence on which is expressed through the dilogarithm function. The
sub-leading term of the entropy counts the winding numbers, showing an analogy
to the topological entanglement entropy which characterizes the topological
order in (2+1)-dimensional systems.
