Research On Broadcast Encryption Schemes Based On Multilinear Maps

Broadcast encryption provides a method to transmit same messages to a number of different users at the same time in an insecurity channel, it has been widely used in the digital pay TV, satellite communications, telephone conference, FM radio and other fields. In the broadcast encryption, the key problem is whether it can guarantee safety and low overhead at the same time, besides, how to extend the traditional broadcast encryption scheme to make it to be applied to the concrete reality is also a key problem. Therefore, how to design a higher performance, more secure and more adaptable to the specific reality scene broadcast encryption scheme becomes an important problem that need to be solved.To solve the above problems, this thesis is based on the theory of multilinear maps and proposes three different kinds of broadcast encryption schemes. The main work of this thesis includes the following aspects:(1)This thesis proposes a plaintext awareness secure broadcast encryption scheme. Because the main performance index of the broadcast encryption scheme is key storage, communication overhead and the amount of calculation, therefore, the study of the broadcast encryption in recent years was mainly focused on how to reduce the length of broadcast ciphertexts, the size of public keys and private keys and the computational complexity which means low overhead. Although the existed broadcast encryption schemes can guarantee the low overhead, they can not ensure adaptive chosen ciphertext attack security at the same time. However, the safety of the broadcast encryption is a crucial problem, so this thesis designs a broadcast encryption scheme which can reach plaintext awareness security in the random oracle model. besides, this scheme can guarantee the length of private keys and ciphertexts are constant. It is a safe and efficient broadcast encryption scheme.(2)This thesis put forward an identity-based broadcast encryption scheme with personalized messages. This scheme is based on the scheme of Ohtakes’ and uses the theory of multilinear maps. It reduces the length of public keys and it is an identitybased broadcast encryption scheme with personalized messages. The scheme can not only ensure the broadcast centre to send broadcast messages, but also guarantee the broadcast centre to send personalized messages to any user of the broadcast users’ set, which means the scheme can provides the transmission of broadcast messages and personalized messages at the same time. The scheme can be effectively applied to the Conditional Access System, which is the core of the pay-TV system now.(3)This thesis proposes an identity-based broadcast encryption scheme based on multilinear maps. Because the identity-based cryptosystem can greatly reduces the management of certificate, and also the communication and the computation bandwidth of the validity verification of public key certificate, this thesis constructs an identity-based broadcast encryption scheme according to the theory of multilinear maps. The scheme can achieve plaintext awareness secure in the random oracle model and at the same time, it can ensure the length of private keys and ciphertexts are constant. Hence, The scheme can ensure safety and efficiency of the sending and receiving of broadcast messages, and it is a more efficient and more secure broadcast encryption scheme.