Identity-based Public Key is an important public key systems. It removes certificate management and certificate update of traditional PKC. Threshold cryptography is an important method to solve key leakage. Recently, Qin etal. proposed an ID-based multi-receiver threshold signcryption scheme and Claimed that their scheme was secure. However, in this paper, we analyze the security of Qin etal's. multi-receiver threshold signcryption scheme, and show that the signcryption scheme are insecure though the schemes was proven to be secure under the random oracle model in [17], the schem doesn't satisfy confidentiality and unforgeability of signcryption. Finally, we give the corresponding attack, and to overcome the above flaws, we also discuss the corresponding improved method.
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