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Inner product functional encryption (IPFE), as a novel cryptographic primitive, can be classified into public-key IPFE (PK-IPFE) and secret-key IPFE (SK-IPFE). PK-IPFE has the following functions: an encryptor generates the ciphertext by encrypting a vector x → , and a decryptor decrypts the ciphertext and obtains the inner product 〈 x → , y → 〉 if it holds the secret key related to vector y → . The general IPFE cannot describe the hierarchical structure. The superior cannot use the general IPFE to issue the delegating keys for the subordinates, which complicates key management. We first propose a new primitive, hierarchical identity-based PK-IPFE (HID-PK-IPFE). HID-PK-IPFE has the following features. First, the identity of the decryptor can be specified when encrypting. Second, the identity of the recipient has a hierarchical structure. In the hierarchical tree, the upper-level users can generate the private key of the lower-level users; that is, our scheme has a delegation function. We formalize the selective chosen plaintext attack model of HID-PK-IPFE, propose the scheme in the standard model, and prove the security of the scheme on the basis of d-DBDHE assumption. We conducted two sets of simulations. We set the maximum depth of the identity hierarchy to 10, and increased the vector length from 10 to 15. We then listed the time spent by each algorithm in these two ranges. The simulation results show that the running time of each algorithm of our HID-PK-IPFE is completely acceptable in actual application scenarios.

With the aggravating trend of aging population in modern societies, Mobile Healthcare Social Network (MHSN) is an attracting platform for improving the life quality of elderly patients and offering mutual supports. In a sustainable MHSN system, one essential issue is to protect sensitive healthcare information while providing information-sharing for patients with multiple symptoms. To achieve multi-symptom matching and cross-domain communications for patients in MHSNs, we propose a new Secret Handshake scheme with Multi-Symptom intersection ( MSSH ), which is derived from a linear-complexity Authorized Private Set Intersection (APSI) based on Schnorr signature. In MSSH , two anonymous patients, who have registered with independent healthcare centers, are able to successfully execute an affiliation-hiding mutual anonymous authentication only if their target authentication policies are satisfied. The authentication policy demands that the designated healthcare center should be matched and the cardinality of their symptoms intersection is not less than a threshold value. Meanwhile, the symptoms outside of the set intersection remain confidential. The formal analysis proves MSSH is secure under the Random Oracle Model (ROM). The experimental results demonstrate that MSSH is efficient and feasible in MHSNs.

Attribute-Based Encryption (ABE), a special type of public key encryption, efficiently shares sensitive data with fine-grained access control. ABE can be classified into two types: Ciphertext-Policy ABE (CP-ABE) and Key-Policy ABE (KP-ABE). However, the securities of most presented ABE systems were reduced to the q-type DBDH (Dicisional Diffie-Hellman Assumption) assumptions, which are stronger than the DBDH assumption. So, the abovementioned ABE systems become insecure if DBDH is proved to be insecure. We propose a new ABE framework, called security-level switchable ABE (SLS-ABE). In SLS-ABE framework, a series of ABE systems can be generated and their securities are reduced to a k-BDH assumption family proposed by Benson et al. The k-BDH assumption family has the following properties: 1) any assumption in the k-BDH assumption family is associated with a parameter k, and the assumption becomes strictly weaker as the parameter k increases. 2) the 1-BDH assumption is proved to be equivalent to the DBDH assumption. So, all the k-BDH assumptions where k > 1 are weaker than DBDH assumption. We apply the technique of Benson et al. to construct ABE on k-BDH assumption, furthermore, we design a new framework to support the flexible switchable security-level for users. Concretely, the master public key, the master secret key and core keys issued by the system are constant. A User can generate different security-level public key/secret key pairs if it holds the core key. We propose a public key forgery attack model (PKFA) to capture the behaviors of adversary for generating a forged public key. We formally prove the selective-CPA security and PKFA security of our ABE systems. We compare the performances of our systems with Waters’ ABE systems.

A DRM system based on P2P whose certificate and digital production can both transmitted among users is presented to solve the bottle-neck problem of the usual system. We make the digital production transmitted quicker and the digital right of the production can be saved in security at the same time. The security proof of the system is given at the end of the paper.