Links among Impossible Differential, Integral and Zero Correlation Linear Cryptanalysis

As two important cryptanalytic methods, impossible differential cryptanalysis and integral cryptanalysis have attracted much attention in recent years. Although relations among other important cryptanalytic approaches have been investigated, the link between these two methods has been missing. The motivation in this paper is to fix this gap and establish links between impossible differential cryptanalysis and integral cryptanalysis. Firstly, by introducing the concept of structure and dual structure, we prove that $a\rightarrow b$ is an impossible differential of a structure $\mathcal E$ if and only if it is a zero correlation linear hull of the dual structure $\mathcal E^\bot$. More specifically, constructing a zero correlation linear hull of a Feistel structure with $SP$-type round function where $P$ is invertible, is equivalent to constructing an impossible differential of the same structure with $P^T$ instead of $P$. Constructing a zero correlation linear hull of an SPN structure is equivalent to constructing an impossible differential of the same structure with $(P^{-1})^T$ instead of $P$. Meanwhile, our proof shows that the automatic search tool presented by Wu and Wang could find all impossible differentials of both Feistel structures with $SP$-type round functions and SPN structures, which is useful in provable security of block ciphers against impossible differential cryptanalysis. Secondly, by establishing some boolean equations, we show that a zero correlation linear hull always indicates the existence of an integral distinguisher while a special integral implies the existence of a zero correlation linear hull. With this observation we improve the integral distinguishers of Feistel structures by $1$ round, build a $24$-round integral distinguisher of CAST-$256$ based on which we propose the best known key recovery attack on reduced round CAST-$256$ in the non-weak key model, present a $12$-round integral distinguisher of SMS4 and an $8$-round integral distinguisher of Camellia without $FL/FL^{-1}$. Moreover, this result provides a novel way for establishing integral distinguishers and converting known plaintext attacks to chosen plaintext attacks. Finally, we conclude that an $r$-round impossible differential of $\mathcal E$ always leads to an $r$-round integral distinguisher of the dual structure $\mathcal E^\bot$. In the case that $\mathcal E$ and $\mathcal E^\bot$ are linearly equivalent, we derive a direct link between impossible differentials and integral distinguishers of $\mathcal E$. Specifically, we obtain that an $r$-round impossible differential of an SPN structure, which adopts a bit permutation as its linear layer, always indicates the existence of an $r$-round integral distinguisher. Based on this newly established link, we deduce that impossible differentials of SNAKE(2), PRESENT, PRINCE and ARIA, which are independent of the choices of the $S$-boxes, always imply the existence of integral distinguishers. Our results could help to classify different cryptanalytic tools. Furthermore, when designing a block cipher, the designers need to demonstrate that the cipher has sufficient security margins against important cryptanalytic approaches, which is a very tough task since there have been so many cryptanalytic tools up to now. Our results certainly facilitate this security evaluation process

Biclique Attack of the Full ARIA-256

In this paper, combining the biclique cryptanalysis with the MITM attack, we present the first key recovery method for the full ARIA-256 faster than brute-force. The attack requires $2^{80}$ chosen plaintexts, and the time complexity is about $2^{255.2}$ full-round ARIA encryptions in the processing phase

A Meet-in-the-Middle Attack on ARIA

In this paper, we study the meet-in-the-middle attack against block cipher ARIA. We find some new 3-round and 4-round distinguish- ing properties of ARIA. Based on the 3-round distinguishing property, we can apply the meet-in-the-middle attack with up to 6 rounds for all versions of ARIA. Based on the 4-round distinguishing property, we can mount a successful attack on 8-round ARIA-256. Furthermore, the 4-round distinguishing property could be improved which leads to a 7-round attack on ARIA-192. The data and time complexities of 7-round attack are 2^120 and 2^185:3, respectively. The data and time complexities of 8-round attack are 2^56 and 2^251:6, respectively. Compared with the existing cryptanalytic results on ARIA, our 5-round attack has the lowest data and time complexities and the 6-round attack has the lowest data complexity. Moreover, it is shown that 8-round ARIA-256 is not immune to the meet-in-the-middle attack

Provable Security Evaluation of Structures against Impossible Differential and Zero Correlation Linear Cryptanalysis

Impossible differential and zero correlation linear cryptanalysis are two of the most important cryptanalytic vectors. To characterize the impossible differentials and zero correlation linear hulls which are independent of the choices of the non-linear components, Sun et al. proposed the structure deduced by a block cipher at CRYPTO 2015. Based on that, we concentrate in this paper on the security of the SPN structure and Feistel structure with SP-type round functions. Firstly, we prove that for an SPN structure, if \alpha_1\rightarrow\beta_1 and \alpha_2\rightarrow\beta_ are possible differentials, \alpha_1|\alpha_2\rightarrow\beta_1|\beta_2 is also a possible differential, i.e., the OR | operation preserves differentials. Secondly, we show that for an SPN structure, there exists an r-round impossible differential if and only if there exists an r-round impossible differential \alpha\not\rightarrow\beta where the Hamming weights of both \alpha and \beta are 1. Thus for an SPN structure operating on m bytes, the computation complexity for deciding whether there exists an impossible differential can be reduced from O(2^{2m}) to O(m^2). Thirdly, we associate a primitive index with the linear layers of SPN structures. Based on the matrices theory over integer rings, we prove that the length of impossible differentials of an SPN structure is upper bounded by the primitive index of the linear layers. As a result we show that, unless the details of the S-boxes are considered, there do not exist 5-round impossible differentials for the AES and ARIA. Lastly, based on the links between impossible differential and zero correlation linear hull, we projected these results on impossible differentials to zero correlation linear hulls. It is interesting to note some of our results also apply to the Feistel structures with SP-type round functions

New Insights on AES-like SPN Ciphers

It has been proved in Eurocrypt 2016 that if the details of the S-boxes are not exploited, an impossible differential and a zero-correlation hull can extend over at most 4 rounds of the AES. This paper concentrates on distinguishing attacks on AES-like SPN ciphers by investigating the details of both the S-boxes and the MDS matrices and illustrates some new insights on the security of these schemes. Firstly, we construct several types of $5$-round zero-correlation linear hulls for AES-like ciphers that adopt identical S-boxes to construct the round function and that have two identical elements in a column of the inverse of their MDS matrices. We then use these linear hulls to construct 5-round integrals provided that the difference of two sub-key bytes is known. Furthermore, we prove that we can always distinguish 5 rounds of such ciphers from random permutations even when the difference of the sub-keys is unknown. Secondly, the constraints for the S-boxes and special property of the MDS matrices can be removed if the cipher is used as a building block of the Miyaguchi-Preneel hash function. As an example, we construct two types of 5-round distinguishers for the hash function Whirlpool. Finally, we show that, in the chosen-ciphertext mode, there exist some nontrivial distinguishers for 5-round AES. To the best of our knowledge, this is the longest distinguishing attack for the round-reduced AES in the secret-key setting. Since the 5-round distinguisher for the AES can only be constructed in the chosen-ciphertext mode, the security margin for the round-reduced AES under the chosen-plaintext attack may be different from that under the chosen-ciphertext attack

Верхние оценки значений индекса ветвления матриц над кольцами вычетов по модулю степени двойки

Індекс розгалуження – один з найважливіших криптографічних параметрів лінійних перетворень у блокових шифрах, який суттєво впливає на стійкість до диференціального та лінійного криптоаналізу. Добре відомі методи побудови у матричній формі лінійних перетворень над скінченними полями, які мають максимально можливе значення індексу розгалуження (MDS-матриці). У той же час важливе криптографічне значення мають операції у кільці лишків за модулем степеня двійки, оскільки вони ефективно реалізуються у сучасних обчислювальних архітектурах і при цьому підвищують стійкість криптоперетворень до алгебраїчних атак. Відомі методи побудови MDS-матриць незастосовні для кілець лишків за непростим модулем. У даній роботі доведено, що матриця над будь-яким кільцем лишків за парним модулем не може мати максимальний індекс розгалуження. Також доведено, що індекс розгалуження матриць над кільцем лишків за модулем степеня двійки є інваріантом при зведенні матриці за модулем 2, а тому для даного класу матриць будуть справедливі усі відомі аналітичні результати, одержані для класу двійкових матриць – зокрема, верхні обмеження на індекс розгалуження. Сформульовано умови для двійкових матриць, необхідні для високого значення індексу розгалуження. Одержані результати дозволяють будувати блокові шифри із потенційно підвищеною стійкістю до алгебраїчних та інтегральних атак, зберігаючи при цьому обґрунтовану стійкість до диференціального та лінійного криптоаналізу.Branch number is a very important cryptographic parameter of linear mappings used in block ciphers. It significantly affects security against differential and linear cryptanalysis due to “wide trail strategy” of block cipher design. Many techniques are well known to generate linear mappings with maximal possible branch number in matrix form over finite fields (so-called MDS-matrices). In the same time operations over integers modulo power of two are important for cryptographic purposes. They are very efficient in modern computing architectures and increase security of cryptographic functions against algebraic attacks. But known techniques of MDS-matrix generating are not applicable to a ring of integers modulo composite number. In this work we proved that any square matrix over a ring of integers modulo even number cannot have a maximal branch number. We proved that the branch number of any square matrix over a ring of integers modulo power of two is invariant under reduction modulo 2. Thus, any analytic result known for binary matrices is valid for matrices modulo power of two, including upper bounds for the branch number. Consequently, the branch number of this type of matrix cannot exceed about two thirds of a matrix size. Also we formulated some requirements for binary matrices to obtain high value of the branch number; we show that such matrices cannot have both sparse (low weight) and dense (high weight) columns. At the end we shortly consider how the security of binary ciphers (e.g. ARIA or Midori) against linear and integral cryptanalysis can be increased by replacing binary matrix with matrix over a ring of integers modulo power of two in linear layer. The results of this work allow to create block ciphers with potentially improved security against algebraic and integral attacks and reasonable security against differential and linear cryptanalysis.Индекс ветвления – один из важнейших криптографических параметров линейных преобразований в блочных шифрах, который существенно влияет на стойкость к дифференциальному и линейному криптоанализу. Хорошо известны методы построения в матричной форме линейных преобразований над конечными полями, которые имеют максимально возможное значение индекса ветвления (MDS-матрицы). В то же время важное криптографическое значение имеют операции в кольцах вычетов по модулю степени двойки, поскольку они эффективно реализуются в современных вычислительных архитектурах и при этом повышают стойкость криптопреобразований к алгебраическим атакам. Известные методы построения MDS-матриц неприменимы для колец вычетов по непростому модулю. В данной работе доказано, что матрица над любым кольцом вычетов по чётному модулю не может иметь максимальный индекс ветвления. Также доказано, что индекс ветвления матрицы над кольцом вычетов по модулю степени двойки инвариантен при сведении матрицы по модулю 2, поэтому для данного класса матриц будут справедливы все известные аналитические результаты, полученные для класса двоичных матриц – в частности, верхние ограничения на индекс ветвления. Сформулированы условия для двоичных матриц, необходимые для высокого значения индекса ветвления. Полученные результаты позволяют строить блочные шифры с потенциально повышенной стойкостью к алгебраическим и интегральным атакам, сохраняя при этом обоснованную стойкость к дифференциальному и линейному криптоанализу

An overview of memristive cryptography

Smaller, smarter and faster edge devices in the Internet of things era demands secure data analysis and transmission under resource constraints of hardware architecture. Lightweight cryptography on edge hardware is an emerging topic that is essential to ensure data security in near-sensor computing systems such as mobiles, drones, smart cameras, and wearables. In this article, the current state of memristive cryptography is placed in the context of lightweight hardware cryptography. The paper provides a brief overview of the traditional hardware lightweight cryptography and cryptanalysis approaches. The contrast for memristive cryptography with respect to traditional approaches is evident through this article, and need to develop a more concrete approach to developing memristive cryptanalysis to test memristive cryptographic approaches is highlighted.Comment: European Physical Journal: Special Topics, Special Issue on "Memristor-based systems: Nonlinearity, dynamics and applicatio

STP Models of Optimal Differential and Linear Trail for S-box Based Ciphers

Automatic tools have played an important role in designing new cryptographic primitives and evaluating the security of ciphers. Simple Theorem Prover constraint solver (STP) has been used to search for differential/linear trails of ciphers. This paper proposes general STP-based models searching for differential and linear trails with the optimal probability and correlation for S-box based ciphers. In order to get trails with the best probability or correlation for ciphers with arbitrary S-box, we give an efficient algorithm to describe probability or correlation of S-Box. Based on the algorithm we present a search model for optimal differential and linear trails, which is efficient for ciphers with S-Boxes whose DDTs/LATs contain entities not equal to the power of two. Meanwhile, the STP-based model for single-key impossible differentials considering key schedule is proposed, which traces the propagation of values from plaintext to ciphertext instead of propagations of differences. And we found that there is no 5-round AES-128 single-key truncated impossible differential considering key schedule, where input and output differences have only one active byte respectively. Finally, our proposed models are utilized to search for trails of bit-wise ciphers GIFT-128, DES, DESL and ICEBERG and word-wise ciphers ARIA, SM4 and SKINNY-128. As a result, improved results are presented in terms of the number of rounds or probabilities/correlations