A NEW GROUP-ORIENTED PUBLICLY VERIABLETHRESHOLD SIGNCRYPTION SCHEME

Through cryptanalysis of the improved scheme of a generalized group-oriented threshold signcryption schemes,it is found that the improved scheme can effectively resist conspiracy attack and forgery attack,but does not have semantic security and public verification function,and sends threshold signcryption by the secret secure channel,which increases the communication costs and potential safety hazards of the system.A new group-oriented publicly verifiable threshold signcryption scheme is proposed on the basis of the improved scheme,the new scheme overcomes the drawbacks of the improved scheme,which not only provides with semantic security and public verification function,but also can send threshold signcryption by the public channel.

Using IND-CVA for constructing secure communication

Within the framework of UC （universally composable） security, a general method is presented to construct a secure channel protocol with using IND-CVA （indistinguishability of encryption scheme under ciphertext verification attacks）. A channel protocol with using the method first invokes an ideal keyexchange protocol to get a session key, and then computes the messages with an authenticated encryption scheme. The paper shows that a channel protocol is UC secure if and only if the underlying authenticated encryption scheme is both IND-CVA secure and INT-PTXT secure. The condition about secure channel protocol in this paper is much weaker than IND-CCA secure and INT-CTXT secure. The IND-CVA can be presented for describing the privacy requirements of secure channels in detail. Moreover, the method for designing secure channel protocol in the paper reduces the UC security of secure channels, which are measured by action-simulation in the UC security framework, to the security of authenticated encryption schemes, which are measured semantically.