Anonymous Attribute-based Encryption For Privacy Protection Of Smart Health Care System

With the rapid development of cloud computing and 5G technology,data sharing based on cloud platform is increasingly recognized by people for its convenience and economy.Especially,these characteristics have significant effects on solving the problems of timeconsuming,low efficiency and uneven resource allocation faced by traditional medicine.Therefore,smart health care(SHC),a cloud-based medical system,has become a hot topic in recent years.However with the frequent occurrence of privacy events in the cloud,privacy protection has become the primary problem to be solved in smart medicine.Attribute-based encryption(ABE)is considered to be one of the most effective mechanism to achieve data and privacy security because of its support for fine-grained access control and source protection of data.However,in smart medicine,some sensitive attributes can indirectly reveal users’ privacy,resulting in the traditional ABE cannot solve such problems.A large number of studies show that ABE based on hiding policy and anonymity can solve the problem of privacy disclosure,but most of them have some problems such as poor decryption efficiency,high storage overhead and inability to resist DDH test attacks.Aiming at these issues,we focus on designing anonymous attribute-based encryption schemes with high efficiency.1.An anonymous attribute-based encryption scheme with fast decryption was constructed for SHC.This scheme adopts LSSS structure with flexible access control and divides the traditional attributes into attribute names and attribute values,which not only solves the inflexibility of AND gate,but also eliminates the problem that schemes based LSSS cannot realize the anonymity of the receiver due to sending access matrix and mapping function.In addition,the proposed scheme also reduces the size of public key and the number of pairing operations in decryption stage to constant level,which enables the scheme to adapt to the environment of large attribute universe and realize fast decryption.2.An attribute-based encryption scheme with hiding access policy is constructed for SHC.Traditional schemes with flexible access control and policy hidden are mostly constructed in composite order bilinear group,which results in high computational and storage overhead.Therefore,the proposed scheme is constructed based on prime order bilinear group.Furthermore,in order to effectively improve the practicability of the scheme in SHC,it added some functions such as large attribute universe,outsourcing decryption,message verification,decryption testing and so on.Finally,the scheme was proved to achieve CPA security under D-Linear assumption and(q-1)-BDHE assumption.3.We make a systematic analysis of the existing anonymous attribute-based encryption schemes,and propose two attack methods and corresponding solutions for receiver anonymity and user privacy protection.1Attack of Attribute Testing: The method breaks the anonymity of such schemes by calculating some or all of the attributes that make up the access policy through a test group with minimal computation.If some attributes of access policy contain sensitive information,it will indirectly disclose the privacy of users.2Guessing Attack of Access Policy: This method can be also regarded as a special case of method one,but the difference is that the former emphasizes the test of a single attribute,while the latter must test the whole access policy.Finally,the solutions of the two attack methods are given where the core is to remove the association of blind factors in ciphertext components.