Identity-based group-recevier signcryption scheme

We present a concrete identity-based broadcast group-receiver encryption and signcryption scheme respectively based on Gentry´s IBE scheme to achieve confidentiality and authentication during content distribution. A sender can send a secure message just by using the receive group´s identity information, even before the receiver in the designated group obtains his private key from a PKG. Every member of the receiving group needs to keep only one private key and can decrypt the ciphertext independently; Both ciphertexts and system parameters are of constant size.