  Recently, Liu et al. [Opt. Commun. 284, 3160, 2011] proposed a protocol for
quantum private comparison of equality (QPCE) based on sym- metric W state.
However, Li et al. [Eur. Phys. J. D. 66, 110, 2012] pointed out that there is a
flaw of information leak, and they proposed a new protocol based on EPR pairs.
While examining these two protocols, we find that there exists a same flaw: the
third party (TP) can know the comparison result. In this paper, through
introducing and constructing a special class of asymmet- ric W state, a secure
QPCE protocol based on this asymmetric W state is presented. Analysis shows the
present protocol can not only effectively avoid the information leak found by
Li et al, but also ensure TP would not get any information about the comparison
result.

Quantum Physics