  We experimentally demonstrate that a long distance actively stabilized
Mach-Zehnder fibre optical interferometer can be used to reliably implement the
GV95 quantum cryptography protocol employing orthogonal states. A
proof-of-principle experiment using an interferometer composed of 1 km of
spooled optical fibres connecting Alice and Bob is performed. The active
stabilisation against phase drifts is done with a classical channel
wavelength-multiplexed with the quantum channel and a high stable visibility
implying a QBER of 2.2 % is shown.
