Efficient quantum secure direct communication with authentication

Two protocols of quantum direct communication with authentication [Phys. Rev. A 73, 042305(2006)], proposed by Lee, Lim and Yang, recently were indicated to be insecure against the authenticator Trentpsilas attacks [Phys. Rev. A 75, 026301(2007)]. In this paper, two novel efficient protocols of quantum direct communication with authentication are presented by utilizing four kinds of Pauli operations (I, sigma
_x
, isigma
_y
, sigma
_z
). These new protocols can transmit two bits message every GHZ state, instead of one bit in the aforementioned protocols. Analysis shows that they are secure against the inner participantpsilas attacks (such as Trentpsilas attacks) as well as the outer Evepsilas attacks. Finally, we generalize them to multiparty quantum direction communication.