Research On Hierarchical Identity-Based Broadcast Encryption

The broadcast is a one-to-many communication mode, which has a higher communication efficiency compared with the traditional point-to-point. Therefore, broadcast has a wide application in the network. Broadcast encryption is an important measure to ensure the information security in the broadcast communication. In which, Identity-based broadcast encryption does not need the public key certificates that simplifies the public key infrastructure and obtain a higher practicability. In the identity-based broadcast encryption schemes, the broadcasters use the identity information of the authorized users to encrypt messages, and then broadcast the ciphertext on a public channel. Only the authorized users can decrypt the ciphertext to get the plaintext, while the unauthorized users are not able to get any useful information.With the increasing scale of the modern network, the network structure is becoming more and more complex. While the traditional broadcast encryption schemes have a low efficiency and a heavy burden which are not suitable for the complex network. Aimed to this problem, the hierarchical identity-based broadcast encryption is proposed in this thesis. In the hierarchical identity-based broadcast encryption, users are distributed in a tree, each layer's users can generate and distribute the private key for the next layer, which solves the problem that a single Private Key Generator has a too heavy burden and it is easy to be a bottleneck. In addition, with the increasing emphasis on the protection of personal privacy, the research on the anonymity of broadcast encryption becomes more and more significant. In some specific scenarios, it is of the same importance and value for the anonymity of the broadcast scheme and the encryption of broadcast information. In an anonymous identity-based broadcast encryption, an attacker are not able to get any information about the receiver that the privacy of users can be protected. Based on the above problems, we put forward the relevant schemes.Firstly, we study the basic algorithm and security model of the identity-based broadcast encryption, and then study the algorithm, security model and the classical scheme of the hierarchical identity-based broadcast encryption, which laid a good foundation for the design of the efficient hierarchical identity-based broadcast encryption schemes.Secondly, based on the Li et al.'s schemes, an improved scheme is proposed. This thesis puts forward a hierarchical identity-based broadcast encryption scheme in the wireless sensor networks. Compared with the original scheme, the proposed scheme reduces the length of the ciphertext, improves the efficiency of encryption and decryption, and obtains a higher security. Furthermore, the proposed scheme can meet the IND-ID-CCA2 security in the random oracle model. In addition, comparing with other similar schemes, we find that our scheme has a higher efficiency and lower cost, that it is more suitable for wireless sensor networks.Then, based on the dual system encryption, this thesis proposes an anonymous hierarchical identity-based broadcast encryption scheme. It can realize efficient broadcast encryption with the hierarchical network topology. Moreover, by adding the anonymous factor in the ciphertext, the scheme realizes the anonymity that protectes the privacy of users. This thesis analyzes the efficiency of the scheme and compares the proposed scheme with some similar schemes, which shows the proposed scheme have a higher efficiency of computation and communication. Furthermore, three static hypotheses are applied to prove that the proposed scheme satisfies the IND-CIVS-CPA security in the standard model. Finally, several practical applications of the proposed scheme are proposed.