  The quantum key distribution for multiparty is one of the essential subjects
of study. Especially, without using entangled states, performing the quantum
key distribution for multiparty is a critical area of research. For this
purpose, sequential discrimination, which provides multiparty quantum
communication and quantum key distribution for {multiple receivers}, has
recently been introduced. However, since there is a possibility of
eavesdropping on the measurement result of a receiver by an intruder using
quantum entanglement, a security analysis for {quantum key distribution} should
be performed. {However,} no one has provided the security analysis for {quantum
key distribution in view of the sequential scheme} yet. In this work, by
proposing a unified model of sequential discrimination including an
eavesdropper, we provide the security analysis of {quantum key distribution
based on the unified model of sequential discrimination strategy.} In this
model, the success probability of eavesdropping and the secret key rate can be
used as a figure of merit. Then, we obtain a non-zero secret key rate between
the sender and receiver, which implies that the sender and receiver can share a
secret key despite eavesdropping. Further, we propose a realistic quantum
optical experiment for the proposed model. We observe that the secret key
between the sender and receiver can be non-zero, even with imperfections. As
opposed to common belief, we further observe that the success probability of
eavesdropping is smaller in the case of colored noise than in the case of white
noise.
