  A continuous variable controlled quantum dialogue scheme is proposed. The
scheme is further modified to obtain two other protocols of continuous variable
secure multiparty computation. The first one of these protocols provides a
solution of two party socialist millionaire problem, while the second protocol
provides a solution for a special type of multi-party socialist millionaire
problem which can be viewed as a protocol for multiparty quantum private
comparison. It is shown that the proposed scheme of continuous variable
controlled quantum dialogue can be performed using bipartite entanglement and
can be reduced to obtain several other two and three party cryptographic
schemes in the limiting cases. The security of the proposed scheme and its
advantage over corresponding discrete variable counterpart are also discussed.
Specifically, the ignorance of an eavesdropper in the proposed scheme is shown
to be very high compared with corresponding discrete variable scheme and thus
the present scheme is less prone to information leakage inherent with the
discrete variable quantum dialogue based schemes.It is further established that
the proposed scheme can be viewed as a continuous variable counterpart of
quantum cryptographic switch which allows a supervisor to control the
information transferred between the two legitimate parties to a continuously
varying degree.
