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Scrutinizing and Improving Impossible Differential Attacks:

by Christina Boura, Valentin Suder
"... Abstract. Impossible differential cryptanalysis has shown to be a very powerful form of cryptanalysis against block ciphers. These attacks, even if extensively used, remain not fully understood because of their high technicality. Indeed, numerous are the applications where mistakes have been discove ..."
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Abstract. Impossible differential cryptanalysis has shown to be a very powerful form of cryptanalysis against block ciphers. These attacks, even if extensively used, remain not fully understood because of their high technicality. Indeed, numerous are the applications where mistakes have been discovered or where the attacks lack optimality. This paper aims in a first step at formalizing and improving this type of attacks and in a second step at applying our work to block ciphers based on the Feistel construction. In this context, we derive generic complexity analysis formulas for mounting such attacks and develop new ideas for optimizing impossible differential cryptanalysis. These ideas include for example the testing of parts of the internal state for reducing the number of involved key bits. We also develop in a more general way the concept of using multiple differential paths, an idea introduced before in a more restrained context. These advances lead to the improvement of previous attacks against well known ciphers such as CLEFIA-128 and Camellia, while also to new attacks against 23-round LBlock and all members of the Simon family.
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Differential Analysis of Block Ciphers SIMON and SPECK

by Alex Biryukov, Arnab Roy, Vesselin Velichkov
"... Abstract. In this paper we continue the previous line of research on the analysis of the differential properties of the lightweight block ciphers Simon and Speck. We apply a recently proposed technique for automatic search for differential trails in ARX ciphers and improve the trails in Simon32 and ..."
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Abstract. In this paper we continue the previous line of research on the analysis of the differential properties of the lightweight block ciphers Simon and Speck. We apply a recently proposed technique for automatic search for differential trails in ARX ciphers and improve the trails in Simon32 and Simon48 previously reported as best. We further extend the search technique for the case of differen-tials and improve the best previously reported differentials on Simon32, Simon48 and Simon64 by exploiting more effectively the strong differential effect of the cipher. We also present improved trails and differentials on Speck32, Speck48 and Speck64. Using these new results we improve the currently best known attacks on several versions of Simon and Speck. A second major contribution of the paper is a graph based algorithm (linear time) for the computation of the exact differential probability of the main building block of Simon: an AND operation preceded by two bitwise shift operations. This gives us a better insight into the differential property of the Simon round function and differential effect in the cipher. Our algorithm is general and works for any rotation constants. The presented techniques are generic and are therefore applicable to a broader class of ARX designs.
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Improved linear trails for the block cipher simon

by Tomer Ashur , 2015
"... Simon is a family of block ciphers designed by the NSA and published in 2013. Due to their simple structure and the fact that the specification lacked security design rationale, the ciphers have been the subject of much cryptanalytic work, especially using differential and linear cryptanalysis. We i ..."
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Simon is a family of block ciphers designed by the NSA and published in 2013. Due to their simple structure and the fact that the specification lacked security design rationale, the ciphers have been the subject of much cryptanalytic work, especially using differential and linear cryptanalysis. We improve previously published linear trail bias estimations by presenting a novel method to calculate the bias of short linear hulls in Simon and use them to construct longer linear approximations. By using these linear approximations we present key recovery attacks of up

Improved Differential Attacks on Reduced SIMON Versions?

by Ning Wang, Xiaoyun Wang, Keting Jia, Jingyuan Zhao
"... Abstract. SIMON is a family of lightweight block ciphers which are designed by the U.S Na-tional Security Agency in 2013. In this paper, we improve the previous differential attacks on SIMON family of block ciphers by considering some bit-difference equations. Combining with some new observations on ..."
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Abstract. SIMON is a family of lightweight block ciphers which are designed by the U.S Na-tional Security Agency in 2013. In this paper, we improve the previous differential attacks on SIMON family of block ciphers by considering some bit-difference equations. Combining with some new observations on key guess policies of SIMON family, we mount differential attacks on 21-
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Improved Linear Cryptanalysis of Round Reduced SIMON

by Javad Alizadeh, Hoda A. Alkhzaimi, Mohammad Reza Aref, Nasour Bagheri, Martin M. Lauridsen
"... Abstract. SIMON is a family of ten lightweight block ciphers published by Beaulieu et al. from U.S. National Security Agency (NSA). A cipher in this family with K-bit key and N-bit block is called SIMON N/K. In this paper we investigate the security of SIMON against different variants of linear cryp ..."
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Abstract. SIMON is a family of ten lightweight block ciphers published by Beaulieu et al. from U.S. National Security Agency (NSA). A cipher in this family with K-bit key and N-bit block is called SIMON N/K. In this paper we investigate the security of SIMON against different variants of linear cryptanalysis, i.e., classic linear, multiple linear and linear hull attacks. We present a connection between linear characteristic and differential characteristic, multiple linear and differential and linear hull and differential, and employ it to adapt the current known results on differential cryptanalysis of SIMON to linear cryptanalysis of this block cipher. Our best linear cryptanalysis covers SIMON 32/64 reduced to 20 rounds out of 32 rounds with the data complexity 231.69 and time complexity 259.69. We have implemented our attacks for small scale variants of SIMON and our experiments confirm the theoretical bias presented in this work. So far, our results are the best known with respect to linear cryptanalysis for any variant of SIMON.
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Linear Cryptanalysis of Reduced-Round SIMECK Variants

by Nasour Bagheri
"... Abstract. SIMECK is a family of 3 lightweight block ciphers designed by Yang et al. They follow the framework used by Beaulieu et al. from the United States National Security Agency (NSA) to design SIMON and SPECK. A cipher in this family with K-bit key and N-bit block is called SIMECKN/K. We show t ..."
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Abstract. SIMECK is a family of 3 lightweight block ciphers designed by Yang et al. They follow the framework used by Beaulieu et al. from the United States National Security Agency (NSA) to design SIMON and SPECK. A cipher in this family with K-bit key and N-bit block is called SIMECKN/K. We show that the security of this block cipher against linear cryptanalysis is not as good as its predecessors SIMON. More precisely, while the best known linear attack for SIMON32/64, using algorithm 1 of Matsui, covers 13 rounds we present a linear attack in this senario which covers 14 rounds of SIMECK32/64. Similarly, using algorithm 1 of Matsui, we present attacks on 19 and 22 rounds of SIMECK48/96 and SIMECK64/128 respectively, compare them with known attacks on 16 and 19 rounds SIMON48/96 and SIMON64/128 respectively. In addition, we use algorithm 2 of Matsui to attack 18, 23 and 27 rounds of SIMECK32/64, SIMECK48/96 and SIMECK64/128 respectively, compare them with known
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Single-Cycle Implementations of Block Ciphers

by Pieter Maene, Ingrid Verbauwhede
"... Abstract. Security mechanisms to protect our systems and data from malicious adversaries have become essential. Strong encryption algo-rithms are an important building block of these solutions. However, each application has its own requirements and it is not always possible to find a cipher that mee ..."
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Abstract. Security mechanisms to protect our systems and data from malicious adversaries have become essential. Strong encryption algo-rithms are an important building block of these solutions. However, each application has its own requirements and it is not always possible to find a cipher that meets them all. This work compares unrolled combina-torial hardware implementations of six lightweight block ciphers, along with an AES implementation as a baseline. Up until now, the majority of such ciphers were designed for area-constrained environments where speed is often not crucial, but recently the need for single-cycle, low-latency block ciphers with limited area requirements has arisen to build security architectures for embedded systems. Our comparison shows that some designers are already on this track, but a lot of work still remains to be done.
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Automated Dynamic Cube Attack on Block Ciphers: Cryptanalysis of SIMON and KATAN

by Zahra Ahmadian, Shahram Rasoolzadeh, Mahmoud Salmasizadeh, Mohammad Reza Aref
"... Abstract. A few work has ever been performed in cryptanalysis of block ciphers using cube attacks. This paper presents a new framework for an efficient key recovery attack on block ciphers based on cube technique. In this method, a cube tester is positioned at the middle of the cipher which is exten ..."
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Abstract. A few work has ever been performed in cryptanalysis of block ciphers using cube attacks. This paper presents a new framework for an efficient key recovery attack on block ciphers based on cube technique. In this method, a cube tester is positioned at the middle of the cipher which is extended in two directions over the maximum possible upper and lower rounds, given that some subkey bits are guessed. It is shown that an automated algorithm for this dynamic cube attack on block ciphers can be realized. Furthermore, we show its effectiveness on two lightweight block ciphers KATAN and SIMON. Our results shows that this method can break 117 and 152 out of 254 rounds of KATAN-32 in non-full-codebook and full-codebook attack scenarios, respectively. In the case of SIMON32/64, we succeed to cryptanalyse 16 and 18 out of 32 rounds, by the same scenarios. Both results show that although this method does not outperform all the existing attacks on these two ciphers, it can absolutely compete with the well-established and mature methods of cryptanalysis of block ciphers, such as linear, differential and meet in the middle attack families.
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Simon and Speck: Block Ciphers for the Internet of Things

by Ray Beaulieu, Douglas Shors, Jason Smith, Stefan Treatman-clark, Bryan Weeks, Louis Wingers , 2015
"... The U.S. National Security Agency (NSA) developed the Simon and Speck families of lightweight block ciphers as an aid for securing applications in very constrained environments where AES may not be suitable. This paper summarizes the algorithms, their design rationale, along with current cryptanalys ..."
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The U.S. National Security Agency (NSA) developed the Simon and Speck families of lightweight block ciphers as an aid for securing applications in very constrained environments where AES may not be suitable. This paper summarizes the algorithms, their design rationale, along with current cryptanalysis and implementation results.
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Automatic Enumeration of (Related-key) Differential and Linear Characteristics with Predefined Properties and Its Applications

by Ling Song
"... Abstract. In this paper, we investigate the Mixed-integer Linear Programming (MILP) modelling of the differential and linear behavior of a wide rang of block ciphers. The differential and linear behavior of the transformations involved in a block cipher can be described by a set P ⊆ {0, 1}n ⊆ Rn. We ..."
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Abstract. In this paper, we investigate the Mixed-integer Linear Programming (MILP) modelling of the differential and linear behavior of a wide rang of block ciphers. The differential and linear behavior of the transformations involved in a block cipher can be described by a set P ⊆ {0, 1}n ⊆ Rn. We show that P is exactly the set of all 0-1 solutions of the H-representation of the convex hull of P. In addition, we can find a small number of inequalities in the H-representation of the convex hull of P such that the set of all 0-1 solutions of these inequalities equals P. Based on these discoveries and MILP technique, we propose an automatic method for finding high probability (related-key) differential or linear characteristics of block ciphers. Compared with Sun et al.’s heuristic method presented in Asiacrypt 2014, the new method is exact for most ciphers in the sense that every feasible 0-1 solution of the MILP model generated by the new method corresponds to a valid characteristic, and therefore there is no need to repeatedly add valid cutting-off inequalities into the MILP model as is done in Sun et al.’s method; the new method is more powerful which allows us to get the exact lower bounds of the number of differentially or linearly active S-boxes; and the new method is more efficient which is able to obtain characteristic enjoying higher probability or covering more rounds of a cipher with less computational effort.