As a distributed extension of ciphertext-policy attribute-based encryption (CP-ABE), multi-authority ABE (MA-ABE) does not require the participation of a trusted central authority and has a wider application prospect in the decentralized background of the cloud computing environment. We propose the first MA-ABE scheme supporting multi-fan-in circuits and collusion-resistance on prime-order bilinear groups and prove the fully adaptive security based on the matrix decision Diffie-Hellman (MDDH) assumption. Compared with the only two fully adaptively secure MA-ABE schemes, our scheme enjoys shorter parameters, which has lower ciphertext and key size, and supports many-use of attribute.

Attribute-based encryption (ABE) is crucial for ciphertext access control in cloud settings. In this paper, we evaluate the resilience of classical ABE schemes to specific attacks, ensuring only robust schemes are employed and informing the design of secure ABE schemes. We demonstrate an attribute-key attack on two ciphertext-policy ABE (CP-ABE) schemes using illegitimate private keys. To quantify the security of private keys against collusion, we propose a novel attribute-key security model. At last, we present a hidden-policy CP-ABE (HP-CP-ABE) scheme, proving its selective security and resistance to collusion attacks.

The identity-based encryption (IBE) scheme takes the user's identity as the public key, which avoids the disadvantages of digital certificate management. Lattice-based IBE scheme has the advantages of resistant to quantum attack, high efficiency and simple structure, and has become a research hotspot in the field of post-quantum information security. In this paper, an IBE scheme is designed based on NTRU lattice, and the hybrid sampling algorithm proposed by Ducas and Prest is used in the private key extraction algorithm of the scheme, which improves the implementation efficiency of the key generation algorithm while ensuring the security of the private key. The encryption and decryption algorithm of the IBE scheme is designed by using the framework structure of the encryption algorithm based on the LWE problem. Under the condition that the NTRU difficulty hypothesis and the LWE difficulty hypothesis hold simultaneously, the scheme is proved to have indistinguishability under chosen plaintext attack with identity-based encryption (IND-ID-CPA). The software implementation of the scheme and the efficiency under the specific parameter settings are given, and the experimental results show that the new scheme has higher encryption and decryption efficiency and shorter ciphertext length than the typical lattice IBE scheme.

Due to the rapid propagation and significant impact, the network public opinion of hot topics has become a concern of the social public and governments. The existing models based on the evolutionary game cannot reflect the real-world propagation of hot topics under uncertain environmental interference. And few researchers analyze the early intervention timing of the government on hot topics based on stochastic evolutionary game theory. To solve these problems, the government intervention parameters of punishment intensity, intervention delay, and intervention probability are introduced to build a three-party stochastic evolutionary game model of “media-netizen-government” in the multi-agent system under the scene of hot topics propagation. Then, the stochastic differential equation is expanded and simulated by the explicit forward Euler numerical method. Finally, simulation experiments are conducted to quantitatively analyze the random evolutionary process and the government intervention timing by adjusting key parameters, which can provide the optimal timing and suggestions for governments to intervene in hot topics propagation.

With the rapid development of multimedia technologies, the multimedia data storage and outsource computation are delegated to the untrusted cloud, which has led to a series of challenging security and privacy threats. Fully homomorphic encryption can be used to protect the privacy of cloud data and solve the trust problem of third party. In this paper, we analyse circular security of matrix GSW-FHE scheme. We derive a sufficient condition of circular security for matrix GSW-FHE scheme. It allows us to choose a good secret key via “reject sample” technique and furthermore obtain circular secure matrix GSW-FHE scheme. We also give an extended version of matrix GSW-FHE by defining deterministic asymmetric encryption algorithm and propose hybrid homomorphic plaintext slot-wise switching method, which significantly reduces computation and storage complexity of bootstrapping key generation, thus optimizing the bootstrapping procedure.

With the rapid development of cloud computation and big data, the data storage and outsource computation are delegated to the untrusted cloud, which has led to a series of challenging security and privacy threats. Fully homomorphic encryption can be used to protect the privacy of cloud data and solve the trust problem of third party. The key problem of achieving fully homomorphic encryption is how to reduce the increasing noise during the ciphertext evaluation. Bootstrapping procedure can refresh ciphertext with large error, such that the resulting ciphertext has potentially smaller error and allows being continuous homomorphic evaluation. In this paper, we investigated the bootstrapping procedure used to construct fully homomorphic encryption scheme. We proposed a new concept of block homomorphic equality test algorithm and gave an instance based on the FH-SIMD scheme. Furthermore, based on the block homomorphic equality test algorithm, we proposed a faster bootstrapping procedure with smaller bootstrapping keys. Both theory analysis and experiment simulation validate high performance of our bootstrapping algorithm.

With the rapid development of Internet of Things (IoT), grave questions of privacy protection are raised. This greatly impacts the large‐scale applications of IoT. Fully homomorphic encryption (FHE) can provide privacy protection for IoT. But, its efficiency needs to be greatly improved. Nowadays, Gentry’s bootstrapping technique is still the only known method of obtaining a “pure” FHE scheme. And it is also the key for the low efficiency of FHE scheme due to the complexity homomorphic decryption. In this paper, the bootstrapping technique of Halevi and Shoup (EUROCRYPT 15) is improved. Firstly, by introducing a definition of “load capacity”, we optimize the parameter range for which their bootstrapping technique works. Next we generalize their ciphertext modulus from closing to a power of two to more general situations. This enables the method to be applied in a larger number of situations. Moreover, this paper also shows how to introduce SIMD homomorphic computation techniques into the new method, to improve the efficiency of recryption.