Recently, Gao et al. [Opt. Commun. 283 (2010) 192] pointed out that Wang et al.'s multiparty controlled quantum secure direct communication (CQSDC) protocol [Opt. Commun. 266 (2006) 732] has the information leakage problem and proposed an improved protocol. However, in the improved protocol, due to the introduction of an additional random sampling to avoid the weakness, the qubit efficiency is decreased. By introducing the base changing technique to the random sampling in Wang et al.'s protocol, this study overcomes the information leakage problem and provides a better qubit efficiency.
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