  We further study the security of the quantum bit commitment (QBC) protocol we
previously proposed [Phys. Rev. A 74, 022332 (2006).], by analyzing the reduced
density matrix \rho_{b}^{B} which describes the quantum state at Bob's side
corresponding to Alice's committed bit b. It is shown that Alice will find
\rho_{0}^{B}\perp \rho_{1}^{B} while the protocol remains concealing to Bob. On
the contrary, the existing no-go theorem of unconditionally secure QBC is based
on the condition \rho_{0}^{B}\simeq \rho_{1}^{B}. Thus the specific cheating
strategy proposed in the no-go theorem does not necessarily applies to our
protocol.
