Key Encapsulation to Designated Group

Most practical applications use hybrid encryption to deal with large plaintext messages since the efficiency of the public key encryption algorithm is low. As a main part of hybrid encryption schemes, Key Encapsulation Mechanism (KEM) allows a sender to generate a random session key and distribute it to recipient. In some communication scenario, one-to-group model is of importance. In this paper, we present a novel key encapsulation to designated group. In our mechanism, anyone can encapsulate a session key for a designated group and any recipient in the designated group can decapsulate the session key with his private key. Finally, we give a proof and show that our new mechanism is secure against adaptively chosen ciphertext attacks in standard model.