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To meet the needs of both encryption and certification for group communication, a generalization of threshold signcryption scheme based on elliptic curve cryptosystem is given. The scheme can simultaneously achieve (t, n) threshold signcryption and (k, l) threshold shared unsigncryption. In threshold shared unsigncryption, the scheme realizes the detection of the malicious members of the group's number by use of Chaum-Pedersen knowledge proof protocol of discrete logarithm equality. By analysis the security and efficiency of the scheme, results indicated that the scheme can safely achieve encryption and certification for group communication at lower computation cost and communication cost.