  According to actual needs, generalized signcryption scheme can flexibly work
as an encryption scheme, a signature scheme or a signcryption scheme. In this
paper, firstly, we give a security model for identity based generalized
signcryption which is more complete than existing model. Secondly, we propose
an identity based generalized signcryption scheme. Thirdly, we give the
security proof of the new scheme in this complete model. Comparing with
existing identity based generalized signcryption, the new scheme has less
implementation complexity. Moreover, the new scheme has comparable computation
complexity with the existing normal signcryption schemes.
