完全安全且固定密文长度的分层内积加密方案

分层内积加密方案为内积加密体制提供了私钥分发功能，可有效降低系统根节点的任务量.针对现有分层内积加密方案密文长度过长的问题，首先提出一个完全安全且固定密文长度的内积加密方案，并以该方案为基础，构造了一个新的分层内积加密方案，利用对偶系统加密的新技术，在标准模型下证明了该分层内积加密方案是完全安全的.新方案密文长度达到了固定值，并且解密时只需要7个双线性对运算.与现有方案比，新方案计算效率高，且易于实现，占用通信带宽低，具有一定的优势.

Fully Secure Hierarchical Inner Product Encryption with Constant-Size Ciphertexts

Inner product encryption (IPE) is a concrete construction of predicate encryption, which represents a wide class of predicates that includes an equality test(for identity-based encryption and hidden vector encryption), disjunctions or conjunctions of equality tests (for attribute-based encryption). Hierarchical inner product encryption (HIPE) can provide the capacity of delegate for inner product encryption, and it can effectively reduce the workload of root node of the system. Aiming at the efficiency that exists in the hierarchical inner product encryption, we present a short ciphertexts IPE scheme with full security in asymmetric bilinear pairing. By making use of the IPE scheme as building blocks, we then present a new HIPE scheme with the new technique for dual system encryption. The new realization of dual system encryption does not use tags, which makes the compression of ciphertexts possible. The proposed HIPE scheme achieves constant-size ciphertexts and full security in the standard model. Security is proven under three static assumptions whose size does not depend on the number of queries. Furthermore, our scheme achieves lower computational cost because decryption only needs seven pairing operations. Compared with other existing schemes, our scheme is more compact to implement and can provide better efficiency in terms of the communication and computation cost.