Abstract: The proxy signature allows a designated person, called a proxy signer, to sign on behalf of an original signer. It has the properties of authenticity and non-repudiation of message except confidentiality. Signcryption is a technique that can encrypt and sign data together in some way, while it has merits of them. I}his paper presented an efficient iden- lily-based threshold signcryption scheme in the standard model and gave its security analysis in terms of bilinear pairing technique. At last, we proved its semantic security on the hardness of Decisional Bilinear DifficHcllman problem and its unforgcability on the hardness of Computational DifficHellman problem.

Key words: Identity based cryptography,Thrcshold proxy signcryption, Bilincar pairing, Computational diffie-hellman problem, Decisional bilinear diffie-hellman problem