  We consider quantum key distribution implementations in which the receiver's
apparatus is fixed and does not depend on his choice of basis at each qubit
transmission. We show that, although theoretical quantum key distribution is
proven secure, such implementations are totally insecure against a strong
eavesdropper that has one-time (single) access to the receiver's equipment. The
attack we present here, the "fixed-apparatus attack" causes a potential risk to
the usefulness of several recent implementations.
