Since the proposition of improved generalised Feistel structure (GFS), many researches and applications have been published. In this study, the authors further enhance the improved GFS with SP-type round function by extending the sub-block-wise permutation to word-wise permutation which can have better diffusion and security effect. Then, they study the security effect of different permutation choices for this kind of enhanced GFS cipher with SP-type round function. By proving several propositions about the equivalent situation, they can eliminate isomorphic permutations so as to narrow down the candidate space notably and propose a method to compute the number of effective permutation candidates. Finally, they take three typical scenes as example, and for each experimental scene, they compute the number of effective permutation candidates and exhaustively evaluate their security results. They also give an optimum permutation as example for each scene.

Along with the development of information technology, the traditional electrical grid is moving to smart grid technology. By using the smart grid, the users and utility providers can more efficiently manage and generate power. Along with the advantages, the smart grid is also faced with new security concerns. In the smart grid, the user's citizen identity information should be preserved and the offensive user should be traced. For some low-capacity devices, it is indispensable to perform complicated computation by using outsourcing computation. The authors provide the outsourcing computation through public cloud. Anonymity and traceability are two important security properties in the smart grid. They are the unity of opposites. On the basis of the security requirements, they propose the balanced anonymity and traceability for outsourcing small-scale data linear aggregation (BAT-LA) in the smart grid. The formal definition, system model and security model are presented. Then, a concrete BAT-LA protocol is designed by using the elliptic curve cryptography and proxy re-encryption. Through security analysis and performance analysis, the designed BAT-LA protocol is provably secure and efficient.

The well-known stream cipher Grain-128a is the new version of Grain-128. While Grain-128 is vulnerable against several introduced attacks, Grain-128a is claimed to be secure against all known attacks and observations on Grain-128. So far the only published single-key attack on Grain-128a is the conditional differential cryptanalysis proposed by Michael Lehmann et al. at CANS 2012. In their analysis, a distinguishing attack on 189-round Grain-128a in a weak-key setting was proposed. In this study, the authors present two new conditional differential attacks on Grain-128a, i.e. attack A and attack B. In attack A, the authors successfully retrieve 18 secret key expressions for 169-round Grain-128a. To the best of our knowledge, attack A is the first attack to retrieve secret key expressions for reduced Grain-128a. In attack B, the authors extend the distinguishing attack against Grain-128a up to 195 rounds in a weak-key setting. Thus far, attack B is the best known attack for reduced Grain-128a as far as the number of rounds attacked is concerned. Hopefully, the authors’ reflections on the design of Grain-128a provide insights on such compact stream ciphers.

The PRINCE cipher is the result of a cooperation between the Technical University of Denmark, NXP Semiconductors and the Ruhr University Bochum. The cipher was designed to reach an extremely low-latency encryption and instant response time. PRINCE has already gained a lot of attention from the academic community, however, most of the attacks are theoretical, usually with very high time or data complexity. This work helps to fill the gap in more practically oriented attacks, with more realistic scenarios and complexities. New attacks are presented, up to seven rounds, relying on integral and higher-order differential cryptanalysis.

Multiple-compression detection is of particular importance in video forensics, as it reveals possible manipulations to the content. However, methods for detecting multiple compressions with same quantisation parameters (QPs) are rarely reported. To deal with this issue, a novel method is presented in this study to detect multiple H.264/advanced video coding compressions with the same QPs. First, a new set, named ratio difference set (RDS), is proposed, which is calculated by identifying the quantised DCT coefficients whose values will be changed after re-compression. Then, a discriminative and fixed statistical feature set extracted from RDS of each video is obtained to serve as input for classification. With the aid of support vector machines, the extracted feature set is used to classify the videos that have undergone H.264 compressions twice or more from those compressed just once. Experimental results show that high classification accuracy and robustness against copy-move attack and frame-deletion attack can be achieved with the authors’ proposed method.

Binary decision diagram (BDD) is a state-of-the-art data structure for representing and manipulating Boolean functions. In 2002, Krause proposed theoretical framework for BDD-based cryptanalysis of stream ciphers. Since then not much work have been reported in this area. In this study, the authors propose a practical approach for cryptanalysis of stream cipher using reduced ordered BDD (ROBDD). They propose various methods for ANDing operation on ROBDDs, required during process of cryptanalysis. Out of these proposed methods, ‘recursive symmetric ANDing’ gives optimal order of ANDing. They use their approach to demonstrate cryptanalysis of E ₀ stream cipher. They also discuss some implementation results. The attack can recover 39 unknown key bits in 5 s on regular personal computer. BuDDy-2.4 library is used for performing operations on BDDs.

As a kind of special proxy signature, directed proxy signature can be used to sign messages, such that only the designated verifier can easily verify the validity of the signature while others cannot. At the same time, if necessary, the proxy signer or designated verifier can prove the validity of the signature to any third party. However, the revocation of delegated rights has never been considered in the existing directed proxy signature schemes. In fact, in these directed proxy signature schemes, even if the period of delegation has expired, the proxy signer still can generate the valid proxy signature, and the original signer can do nothing to prevent it. Therefore, the authors give a solution to the delegation revocation problem and propose a directed proxy signature scheme with fast revocation in this study. The security and the invisibility of the authors’ scheme are proven based on the gap Diffie–Hellman assumption and under the decisional Diffie–Hellman problem in the standard model, respectively.