Information Leakage in Quantum Secret Sharing of Multi-Bits by an Entangled Six-Qubit State

In a recent paper Long et al. (J. Phys. A: Math. Theor. 45: 195303, 2012), a quantum secret sharing protocol was presented, in which the genuinely maximally entangled six-qubit states were used. According to the protocol, Alice could share three bits among three agents, which showed that it was more efficient than previous protocols. Here, we analyze it and point out that the information about the transmitted secret will be partly leaked out unknowingly. Through the classical public channel, 2/3 of Alice’s secret messages is leaked out to Bob₁ and Bob₂, and 1/3 secret messages is leaked out to Bob₃, respectively. This phenomenon should be strictly forbidden in a quantum secret sharing protocol.