  In this article, we are interested in the physical model of general quantum
protocols implementing secure two-party computations in the light of Mayers'
and Lo's & Chau's no-go theorems of bit commitment and oblivious transfer. In
contrast to the commonly adobted quantum pure two-party model in the literature
where classical communication is normally ignored, we propose an alternative
interpretation for the purification of classical communication in two-party
protocols by introducing a quantum third party for the classical channel. This
interpretation leads to a global three-party model, involving Alice's and Bob's
machines and the environment coupled to the macroscopic channel, using the
decoherence scheme in quantum measurements. This model could give a more
general view on the concealing/binding trade-off of quantum bit commitment
protocols.
  Inspired from this three-party interpretation, we extend the no-go theorems
for denying some classes of two-party protocols having access to some
particular quantum trusted third-parties, known as quantum two-party oracles.
The extension implies that a quantum protocol for implementing secure two-party
computations musts have access to a trusted third-party which erases
information and thus makes dissipation of heat to the environment.
