Generating graphs packed with paths: Estimation of linear approximations and differentials:Estimation of linear approximations and differentials

When designing a new symmetric-key primitive, the designer must show resistance to known attacks. Perhaps most prominent amongst these are linear and differential cryptanalysis. However, it is notoriously difficult to accurately demonstrate e.g. a block cipher’s resistance to these attacks, and thus most designers resort to deriving bounds on the linear correlations and differential probabilities of their design. On the other side of the spectrum, the cryptanalyst is interested in accurately assessing the strength of a linear or differential attack. While several tools have been developed to search for optimal linear and differential trails, e.g. MILP and SAT based methods, only few approaches specifically try to find as many trails of a single approximation or differential as possible. This can result in an overestimate of a cipher’s resistance to linear and differential attacks, as was for example the case for PRESENT. In this work, we present a new algorithm for linear and differential trail search. The algorithm represents the problem of estimating approximations and differentials as the problem of finding many long paths through a multistage graph. We demonstrate that this approach allows us to find a very large number of good trails for each approximation or differential. Moreover, we show how the algorithm can be used to efficiently estimate the key dependent correlation distribution of a linear approximation, facilitating advanced linear attacks. We apply the algorithm to 17 different ciphers, and present new and improved results on several of these

The Simeck Family of Lightweight Block Ciphers

Two lightweight block cipher families, SIMON and SPECK, have been proposed by researchers from the NSA recently. In this paper, we introduce Simeck, a new family of lightweight block ciphers that combines the good design components from both SIMON and SPECK, in order to devise even more compact and efficient block ciphers. For Simeck32/64, we can achieve 505 GEs (before the Place and Route phase) and 549 GEs (after the Place and Route phase), with the power consumption of 0.417 $\mu W$ in CMOS 130nm ASIC, and 454 GEs (before the Place and Route phase) and 488 GEs (after the Place and Route phase), with the power consumption of 1.292 $\mu W$ in CMOS 65nm ASIC. Furthermore, all of the instances of Simeck are smaller than the ones of hardware-optimized cipher SIMON in terms of area and power consumption in both CMOS 130nm and CMOS 65nm techniques. In addition, we also give the security evaluation of Simeck with respect to many traditional cryptanalysis methods, including differential attacks, linear attacks, impossible differential attacks, meet-in-the-middle attacks, and slide attacks. Overall, all of the instances of Simeck can satisfy the area, power, and throughput requirements in passive RFID tags

Bit-Sliding: A Generic Technique for Bit-Serial Implementations of SPN-based Primitives -- Applications to AES, PRESENT and SKINNY

Area minimization is one of the main efficiency criterion for lightweight encryption primitives. While reducing the implementation data path is a natural strategy for achieving this goal, Substitution-Permutation Network (SPN) ciphers are usually hard to implement in a bit-serial way (1-bit data path). More generally, this is hard for any data path smaller than its Sbox size, since many scan flip-flops would be required for storage, which are more area-expensive than regular flip-flops. In this article, we propose the first strategy to obtain extremely small bit-serial ASIC implementations of SPN primitives. Our technique, which we call bit-sliding, is generic and offers many new interesting implementation trade-offs. It manages to minimize the area by reducing the data path to a single bit, while avoiding the use of many scan flip-flops. Following this general architecture, we could obtain the first bit-serial and the smallest implementation of AES-128 to date (1563 GE for encryption only, and 1744 GE for encryption and decryption with IBM 130nm standard-cell library), greatly improving over the smallest known implementations (about 30% decrease), making AES-128 competitive to many ciphers specifically designed for lightweight cryptography. To exhibit the generality of our strategy, we also applied it to the PRESENT and SKINNY block ciphers, again offering the smallest implementations of these ciphers thus far, reaching an area as low as 1054 GE for a 64-bit block 128-bit key cipher. It is also to be noted that our bit-sliding seems to obtain very good power consumption figures, which makes this implementation strategy a good candidate for passive RFID tags

Entropy in Image Analysis II

Image analysis is a fundamental task for any application where extracting information from images is required. The analysis requires highly sophisticated numerical and analytical methods, particularly for those applications in medicine, security, and other fields where the results of the processing consist of data of vital importance. This fact is evident from all the articles composing the Special Issue "Entropy in Image Analysis II", in which the authors used widely tested methods to verify their results. In the process of reading the present volume, the reader will appreciate the richness of their methods and applications, in particular for medical imaging and image security, and a remarkable cross-fertilization among the proposed research areas

Towards a standardised attack graph visual syntax

More research needs to focus on developing effective methods of aiding the understanding and perception of cyber-attacks. Attack modelling techniques (AMTs) - such as attack graphs, attack trees and fault trees, are popular methods of mathematically and visually representing the sequence of events that lead to a successful cyber-attack. Although useful in aiding cyber-attack perception, there is little empirical or comparative research which evaluates the effectiveness of these methods. Furthermore, there is no standardised attack graph visual syntax configuration, currently more than seventy-five self-nominated attack graph and twenty attack tree configurations have been described in the literature - each of which presents attributes such as preconditions and exploits in a different way. This research analyses methods of presenting cyber-attacks and reveals that attack graphs and attack trees are the dominant methods. The research proposes an attack graph visual syntax which is designed using evidence based principles. The proposed attack graph is compared with the fault tree - which is a standard method of representing events such as cyber-attacks. This comparison shows that the proposed attack graph visual syntax is more effective than the fault tree method at aiding cyber-attack perception and that the attack graph can be an effective tool for aiding cyber-attack perception - particularly in educational contexts. Although the proposed attack graph visual syntax is shown to be cognitively effective, this is no indication of practitioner acceptance. The research proceeds to identify a preferred attack graph visual syntax from a range of visual syntaxes - one of which is the proposed attack graph visual syntax. The method used to perform the comparison is conjoint analysis which is innovative for this field. The results of the second study reveal that the proposed attack graph visual syntax is one of the preferred configurations. This attack graph has the following attributes. The flow of events is represented top-down, preconditions are represented as rectangles, and exploits are represented as ellipses. The key contribution of this research is the development of an attack graph visual syntax which is effective in aiding the understanding of cyber-attacks particularly in educational contexts. The proposed method is a significant step towards standardising the attack graph visual syntax