Abstract
I present a new protocol for three-party quantum secure direct communication (QSDC) with a set of ordered M Einstein—Podolsky—Rosen (EPR) pairs. In the scheme, by performing two unitary operations and Bell state measurements, it is shown that the three legitimate parties can exchange their respective secret message simultaneously. Then I modify it for an experimentally feasible and secure quantum sealed-bid auction (QSBD) protocol. Furthermore, I also analyze the security of the protocol, and the scheme is proven to be secure against the intercept-and-resend attack, the disturbance attack and the entangled-and-measure attack.