  Recently, Yan et al. proposed a quantum secure direct communication (QSDC)
protocol with authentication using single photons and Einstein-Podolsky-Rosen
(EPR) pairs (Yan et al., CMC-Computers, Materials \& Continua, 63(3), 2020). In
this work, we show that the QSDC protocol is not secure against
intercept-and-resend attack and impersonation attack. An eavesdropper can get
the full secret message by applying these attacks. We propose a modification of
this protocol, which defeats the above attacks along with all the familiar
attacks.
