A Study Of Fully Secure Hierarchy Attribute-Based Encryption

Attribute-Based Encryption(ABE) is not only a new type of public key encryption which supports multi-to-multi model, but also an important extension of identity-based encryption system. In the attribute-based encryption, the user's identity information is no longer a simple single message, but composed by a series of descriptive attributes, and a more flexible access structure is added to this system. The most advantage of this system is that the sender does not need to specify a specific recipient when he encrypts the message, and the receiver only who meets the corresponding conditions can decrypt the message. Attribute-based encryption can be divided into two categories depending on the access policy: key-policy attribute-based encryption(KP-ABE) and ciphertext-policy attribute-based encryption(CP-ABE).In the previous attribute-based encryption scheme, attributes are in the same hierarchy,which no importance. while in the real world, the universal attributes are classified into different levels according to their importance. Therefore, in 2014, Liu et al. presented a scheme with the name of ciphertext-policy hierarchical attribute-based encryption(CP-HABE),The universal attributes in this scheme are classified into different hierarchies according to their importance defined in the access control structure. Each user in the system has a hierarchical set of attributes. The sender encrypts a message to users in the system who have a certain set of attributes. The ciphertext contains a kind of hierarchical access structure. In order to decrypt the message, users' attributes in hierarchy must satisfy the hierarchical access structure. This CP-HABE can be regarded as a form of traditional CP-ABE scheme in which all attributes are in the same level.This paper first systematically introduces some research background and basic theoretical knowledge of attribute-based encryption. And then focus on the hierarchical secret sharing scheme and Waters' s ciphertext-policy encryption scheme and the ciphertext-policy hierarchical attribute-based encryption(CP-HABE) which proposed by Liu et al. we do the following aspects of improvements aiming at Liu's scheme:1)In this paper, we present a fully secure hierarchical ciphertext-policy attribute-based encryption scheme on the basis of Liu et al. Our scheme is proved fully secure under the standard model which depends on three assumptions, and we prove it fully secure by using a dual system encryption methodology, and finally, we give a detailed description of our scheme's constrastive analysis.2) The hierarchical access structure used in the original program are replaced by improvement of the hierarchical access structure the proposed by Mao et al. So that a large amount of computation have a large decrease when we construct the access structure, which is more efficient.3) Liu's scheme in the encryption listed the layer 0 attributes separately for encryption, but in our paper, we will use a kind of expression to encrypt all levels of attributes, thus simplify the cipher. In addition, the Liu's scheme in the decryption did not consider the comprehensive cases causing some decryption failed. And we fully take this into account and reconstruct the decryption algorithm. Verification results can successfully decrypt all case.