With the popularisation of Android smartphones, the value of mobile application security research has increased. The emergence of adversarial technology makes it possible for malware to evade detection. Therefore, research is conducted on Android malicious applications of adversarial attack. To clarify the process and theory of adversarial sample generation, an adversarial sample generation algorithm is proposed that filters features based on feature spatial distribution and definition. These features are modified on real malicious samples to form adversarial samples. In addition, to enhance the robustness of adversarial sample classification detection, a multiple feature set detection algorithm is designed and implemented. Using the frequency differential enhancement feature selection algorithm to perform feature screening, the algorithm forms two different feature sets and establishes two different training sets to train different classification algorithms. Prediction results obtained by the two classification algorithms are integrated based on certain rules. Experimental results on the VirusShare dataset show that both algorithms are effective. The detection results in an actual environment also prove the effectiveness of the multiple feature set detection algorithm.

A simultaneous Diophantine approximation (SDA) algorithm takes instances of the partial approximate common divisor (PACD) problem as input and outputs a solution. While several encryption schemes have been published and their securities depend on the presumed hardness of variant of the PACD problem, fewer studies have attempted to extend the SDA algorithm to be applicable to these variants. In this study, the SDA algorithm is extended to solve the general PACD problem. In order to proceed, first the variants of the PACD problem are classified and how to extend the SDA algorithm for each is suggested. Technically, the authors show that a short vector of some lattice used in the SDA algorithm gives an algebraic relation between secret parameters. Then, all the secret parameters can be recovered by finding this short vector. It is also confirmed experimentally that this algorithm works well.

Attribute‐based encryption (ABE) is a promising management method that enables fine‐grained access control in large‐scale systems. Revocable ABE (RABE) can support a key revocation mechanism in an ABE system. With the advent of the Internet of Things, users may need to delegate their decryption capacity to other devices, which requires that RABE meet a necessary feature called decryption key exposure resistance (DKER). Although many constructions about RABE from bilinear maps have been proposed, the situation of lattice‐based constructions with DKER is less satisfactory. In order to narrow this gap, this paper propose the first lattice‐based RABE with DKER. First, a formal description of RABE with DKER and the corresponding security models is proposed. Subsequently, a lattice‐based RABE scheme without DKER is constructed and it is proved to be selective indistinguishability under chosen‐plaintext attack (IND‐CPA) security based on Learning with Errors (LWE). To achieve DKER, this paper construct a RABE scheme by using the RABE scheme without DKER and a key extension mechanism as its building blocks. Finally, this paper show that this scheme is selective IND‐CPA security, with the DKER based on LWE.

The existing privacy protection schemes for Location‐Based Service (LBS) only protect users' location privacy or query privacy, which can not adopt both of the privacy protections simultaneously in the LBS system. Moreover, these schemes cannot take into account the spatial‐temporal correlation and background knowledge. In response to the above mentioned questions, the LBS Privacy Protection Scheme Based on Differential Privacy (DPLQ) is proposed. The method contains two kinds of privacy protection algorithms: users' location privacy protection algorithm and users' query privacy protection algorithm. The users' location privacy protection algorithm divides the map using the Voronoi diagram, choosing l fake location points based on the improved k‐means algorithm and l‐diversity idea, and protects users' location privacy with the Laplace mechanism. Based on the k‐anonymous algorithm, the users' query privacy protection algorithm builds a query k‐anonymous set according to the neighbour users' query requests at the same time t in the cluster and the historical query probability of the region’s POI and protects users' query privacy with the exponential mechanism. Through setting the privacy protection intensity of the algorithm by the users, the generated location dataset and query k‐anonymous set can resist a variety of attacks from malicious attackers. Theoretical analysis and experimental results show that the scheme can effectively protect the location privacy and query privacy of users.

This work presents a structural attack against the type‐II generalised Feistel network (GFN) with secret internal functions. First, equivalent structures of the 7‐round type‐II GFN are provided, which helps reduce the first guess of the secret round functions. Then, two yoyo game distinguishers are simultaneously employed for these structures to reduce the data complexity by half. Based on these two distinguishers, it is found that the original yoyo game algorithm, proposed to attack the 5‐round Feistel structure, is not suitable for these structures, owing to the characteristics of the yoyo game cycle. To solve this problem, the partial look‐up table recycling technique is presented, which can utilise collision cycles with insufficient information. This technique performs better as the width of each branch ‘n’ grows. For yoyo game attacks, this study systematically investigates its cycle characteristics to determine the reason for the short collision cycle. For 7‐round type‐II GFNs, this work presents the first decomposition thus far, which can be executed within a time complexity of O(n2^4n + 3) and a data complexity of O(2^3n + 2). We believe this work enriches the yoyo game attack and the application of type‐II GFNs.

Multi‐key fully homomorphic encryption (MKFHE) allows computations on ciphertexts encrypted by different users, which can be applied to implement secure multi‐party computing (MPC). The current NTRU‐based MKFHE has the following two drawbacks: One is that the relinearisation process during homomorphic evaluation is so complicated that the corresponding computation time is costly. The other is that a class of subfield attacks are proposed and affects the security of NTRU schemes over power‐of‐2 cyclotomic rings for large moduli q, especially for the NTRU‐based fully homomorphic encryption (FHE) schemes. In this work, an efficient MKFHE scheme is proposed over prime cyclotomic rings with fewer relinearisations, which seems a good choice because of its potential to resist a subfield attack. More specifically, the time of the relinearisation process is reduced by half in homomorphic evaluations by separating the homomorphic multiplication and the relinearisation process (implementing two homomorphic multiplication operations together before relinearisation), while in current NTRU‐type MKFHE schemes, these two processes are usually performed together. The error bound of the basic function components is re‐analysed over prime cyclotomic rings in the average case, which can be used in the error analysis of our scheme. We construct an efficient NTRU‐based single‐key FHE scheme and an efficient MKFHE scheme over prime cyclotomic rings through relinearisation and modulus‐switching techniques. The MKFHE scheme proposed has the on‐the‐fly property and has a tight ciphertext size compared with the GSW‐type and BGV‐type MKFHE schemes. An experiment shows that the homomorphic evaluation of the optimised single‐key FHE scheme proposed is 1.9 times faster than an efficient NTRU‐type MKFHE DHS16 proposed at DCC 2016.

Symmetric cryptography is expected to be quantum safe when long‐term security is needed. Kuwakado and Morii gave a 3‐round quantum distinguisher of the Feistel cipher based on Simon's algorithm. However, the quantum distinguisher without considering the specific structure of the round function is not accurate enough. A new quantum cryptanalysis method for Feistel structure is studied here. It can make full use of the specific structure of the round function. The properties of Camellia round function and its linear transformation P are taken into account, and a 5‐round quantum distinguisher is proposed. Then, the authors follow a key‐recovery attack framework by Leander and May, that is, Grover‐meet‐Simon algorithm, and give a quantum key‐recovery attack on 7‐round Camellia in Q2 model with the time complexity of 2²⁴. It is the very first time that the specific structure of the round function is used to improve quantum attack on Camellia.