  We find a resonance behavior in the disturbance when an eavesdropper chooses
a near-optimal strategy intentionally or unintentionally when the usual
Bennett-Brassard cryptographic scheme is performed between two trusted parties.
This phenomenon tends to disappear when eavesdropping strategy moves far from
the optimal one. Therefore, we conjecture that this resonant effect is a
characteristic for the eavesdropping strategy near to optimal one. We argue
that this effect makes the quantum cryptography more secure against the
eavesdropper's attack.
