Strongest AES with S-Boxes Bank and Dynamic Key MDS Matrix (SDK-AES)

Total Page:16

File Type:pdf, Size:1020Kb

Strongest AES with S-Boxes Bank and Dynamic Key MDS Matrix (SDK-AES) International Journal of Computer and Communication Engineering, Vol. 2, No. 4, July 2013 Strongest AES with S-Boxes Bank and Dynamic Key MDS Matrix (SDK-AES) Fatma Ahmed and Dalia Elkamchouchi the State by cyclically shifting the last three rows of the State Abstract—With computers, security is only a matter of by different offsets to provide inter-column diffusion. software. The Internet has made computer security much more Mix columns: Transformation in the Cipher that takes all difficult than it used to be. In this paper, we introduce modified AES with S-boxes bank to be acted like rotor mechanism and of the columns of the State and mixes their data dynamic key MDS matrix (SDK-AES). In this paper we try to (independently of one another) to produce new columns make AES key dependent and resist the frequency attack. The which provides inter-Byte diffusion. SDK-AES algorithm is compared with AES and gives excellent Add round key: Transformation in the Cipher and Inverse results from the viewpoint of the security characteristics and Cipher in which a RoundKey is added to the State using an the statistics of the ciphertext. Also, we apply the randomness tests to the SDK-AES algorithm and the results shown that the XOR operation which provides confusion. new design passes all tests which proven its security. This paper introduces a new modification on AES algorithm to exhibit a substantial avalanche effect, to ensure Index Terms—Advanced encryption algorithm (AES), that no trapdoor is present in the cipher, to make the key S-boxes bank, rotor, frequency analysis, inverse power function, schedule so strong that the knowledge of one round key does MDS. not help in finding the cipher key or other round keys, and to I. INTRODUCTION resist the frequency analysis on ciphertext. B. The MDS Matrix A. AES Maximum distance separable matrixes (MDS) are widely AES is short for Advanced Encryption Standard and is a used in design of block ciphers and hash functions etc. Based United States encryption standard defined in Federal on the character of its differential branch number, MDS Information Processing Standard (FIPS) 192, published in matrix is widely used and the arithmetic using MDS matrixes November 2001 [1]. It was approved as a federal standard in can effective against differential cryptanalysis and linear May 2002. AES is the most recent of the four current cryptanalysis. A linear code over Galois field GF (2p ) is algorithms ratified for federal us in the United States. Rijndael submitted by Joan Daemen and Vincent Rijmen, is a denoted as an (,,)n k d code, where n is the symbol length symmetric key, iterated block cipher based on the arithmetic of the encoded message, k is the symbol length of the in the Galois Field GF (28 ) . AES Input and Output consists of original message, and d is the minimal symbol distance 128 bit sequences. The cipher key is 128, 192, or 256 bits. between any two encoded messages[3]. Byte is the unit of processing. Input blocks are 16 bytes each. Definition 1: Let K be a finite field and p and q be two AES operations are Conducted on a two dimensional array of integers. Let x M x be a mapping from K p to bytes called the state. The state consists of four rows of bytes q K defined by the qp matrix M . We say that it is a linear each containing N bytes where N is the block length divided b b multipermutation (or an MDS matrix) if the set of all pairs by 32. Rijndael round function acts on a state times, where N r (,)x M x is an MDS code, i.e. a linear code of is equal to the number of rounds that can be 10, 12 or 14 N r dimension p , length pq and minimal distance q 1 [4]. rounds, depending on N , where is equal to the number of k N k The following theorem [5] will depict the character of 32-bit words comprising the Cipher Key [2]. Rijndael round MDS matrix from the angle of a subdeterminant. is consists of 4 transformations: Theorem 1: A matrix is an MDS matrix if and only if Sub bytes: Transformation in the Cipher that processes every sub-matrix is non-singular. the State using a nonlinear byte substitution table (S-box) that MDS matrices are constructed by two types of matrices: operates on each of the State bytes independently which circulant and Hadamard matrices. provides nonlinearity and confusion. Circulant matrices: Given k elements, ....., , a Shift rows: Transformation in the Cipher that processes 0 1k 1 circulant matrix M is constructed with each entry M . Manuscript received January 11, 2013; revised April 12, 2013. i, j ( i j )mod k Fatma Ahmed is with the Dept. of Electrical Engineering, Alexandria Hadamard matrices: Given k elements, ......., , Higher Institute of Engineering and Technology (AIET) Alexandria, Egypt 0 1k 1 (e-mail: [email protected]). a Hadamard matrix M is constructed with each entry Dalia Elkamchouchi is with the Dept of Electrical Engineering, Faculty of M . Engineering, Alexandria University Alexandria, Egypt (e-mail: i,() j i j [email protected]). DOI: 10.7763/IJCCE.2013.V2.242 530 International Journal of Computer and Communication Engineering, Vol. 2, No. 4, July 2013 II. SDK-AES operation will be repeated every 256 bytes. In our system, SDK-AES is block cipher; it can encrypt blocks the second S-box will be rotated by irregular step. This ofplaintext of length 128 byte into blocks of the same length. rotation consists of two steps: the first step is rotating the The key length can be 128, 192, or 256 bytes. The total second S-box in the tenth round after mapping each byte by number of rounds depends on the key length that can be 10, odd numbers (1, 3, 5 and 7). First we rotate the second S-box 12 or 14 respectively. We assume a key length of 128 byte, by one byte until we reach 256 bytes then we rotate it by three which is likely to be the one most commonly implemented. bytes for the next 256 input bytes. Then we rotate it by five The input to the encryption and decryption algorithms is bytes for the next 256 input bytes. Finally we rotate it by block of length 128 byte. This block is copied into the 16×8 seven bytes until we have 256 input bytes. At the second step matrix of bytes, which is modified at each stage of encryption we rotate the second S-box after the tenth round is completed or decryption. After the final stage, State is copied to an by one byte. These two steps guarantee that the S-box rotates output matrix. Similarly the 128 byte key is depicted as 16×8 in irregular manner because after encrypt each block of matrix of bytes. This key is then expanded into an array of plaintext the second S-box will be in different arrangement so key schedule words; each word is four bytes and the total key even we have repeated data, the output will be totally schedule is 32×11 words. The encryption and decryption different. The basic idea is make the S-box like rotor process of SDK-AES resembles that of AES. The Fig. 1 cryptosystem with maintain the security and the simple shows the overall structure of SDK-AES. decryption. In decryption algorithm we don't rotate the S-boxes or even scanned for output like rotor, we only subtract the output from the inverse-second S-box with the number of times that second S-box bytes rotated. We rotate the second S-box only and keep the first one stationary because the second one only known to sender and receiver. B. ShiftRows Transformation The input data is arranged in sixteen rows and eight columns. The forward shift row transformation is performed in following way: The first and ninth row of State is not altered. For the second row, a 1-byte circular left shift is performed. For the third row, a 2-byte circular left shift is performed. And so on until the eighth row, a 7-byte circular left shift is performed [7]. Then we circular left shift the tenth row by one byte, the eleventh row by two bytes and so on until the sixteen row, a seven-byte circular left shift is performed. The inverse shift row transformation performs the circular shifts in the opposite direction for each of the fourteenth rows. (a) Encryption structure (b) Decryption structure C. The New Efficient MDS Matrix Fig. 1. SDK-AES algorithm In SDK-AES, we design new dynamic MDS matrixes A. S-Boxes Bank which depend on the user key. The number of matrixes is SDK-AES is a technique seeking to make AES key eight each one depends on the user key. In encryption process depending. In this paper, key dependent S-boxes bank act we only use one matrix from eight for every data block. The like rotor mechanism [6] is introduced. The S-boxes bank choice of this one depends on the subkeys and plaintext. The contains two S-boxes, the first S-box is one used for AES new matrixes are self inverse so that same matrix can be used algorithm. In order to maintain the structure of cipher to be for decryption algorithm, which decreases the complexity of simple, the second S-box constructs from shifted the first system. The new MDS matrix is 44 Circulant matrix.
Recommended publications
  • VHDL Implementation of Twofish Algorithm
    VHDL Implementation of Twofish Algorithm Purnima Gehlot Richa Sharma S. R. Biradar Mody Institute of Mody Institute of Mody Institute of Technology Technology Technology and Science and Science and Science Laxmangarh, Sikar Laxmangarh, Sikar Laxmangarh, Sikar Rajasthan,India Rajasthan,India Rajasthan,India [email protected] [email protected] [email protected] which consists of two modules of function g, one MDS i.e. maximum ABSTRACT distance separable matrix,a PHT i.e. pseudo hadamard transform and Every day hundreds and thousands of people interact electronically, two adders of 32-bit for one round. To increase the complexity of the whether it is through emails, e-commerce, etc. through internet. For algorithm we can perform Endian function over the input bit stream. sending sensitive messages over the internet, we need security. In this Different modules of twofish algorithms are: paper a security algorithms, Twofish (Symmetric key cryptographic algorithm) [1] has been explained. All the important modules of 2.1 ENDIAN FUNCTION Twofish algorithm, which are Function F and g, MDS, PHT, are implemented on Xilinx – 6.1 xst software and there delay calculations Endian Function is a transformation of the input data. It is used as an interface between the input data provided to the circuit and the rest has been done on FPGA families which are Spartan2, Spartan2E and of the cipher. It can be used with all the key-sizes [5]. Here 128-bit VirtexE. input is divided into 16 bytes from byte0 to byte15 and are rearranged to get the output of 128-bit. Keywords Twofish, MDS, PHT, symmetric key, Function F and g.
    [Show full text]
  • The Whirlpool Secure Hash Function
    Cryptologia, 30:55–67, 2006 Copyright Taylor & Francis Group, LLC ISSN: 0161-1194 print DOI: 10.1080/01611190500380090 The Whirlpool Secure Hash Function WILLIAM STALLINGS Abstract In this paper, we describe Whirlpool, which is a block-cipher-based secure hash function. Whirlpool produces a hash code of 512 bits for an input message of maximum length less than 2256 bits. The underlying block cipher, based on the Advanced Encryption Standard (AES), takes a 512-bit key and oper- ates on 512-bit blocks of plaintext. Whirlpool has been endorsed by NESSIE (New European Schemes for Signatures, Integrity, and Encryption), which is a European Union-sponsored effort to put forward a portfolio of strong crypto- graphic primitives of various types. Keywords advanced encryption standard, block cipher, hash function, sym- metric cipher, Whirlpool Introduction In this paper, we examine the hash function Whirlpool [1]. Whirlpool was developed by Vincent Rijmen, a Belgian who is co-inventor of Rijndael, adopted as the Advanced Encryption Standard (AES); and by Paulo Barreto, a Brazilian crypto- grapher. Whirlpool is one of only two hash functions endorsed by NESSIE (New European Schemes for Signatures, Integrity, and Encryption) [13].1 The NESSIE project is a European Union-sponsored effort to put forward a portfolio of strong cryptographic primitives of various types, including block ciphers, symmetric ciphers, hash functions, and message authentication codes. Background An essential element of most digital signature and message authentication schemes is a hash function. A hash function accepts a variable-size message M as input and pro- duces a fixed-size hash code HðMÞ, sometimes called a message digest, as output.
    [Show full text]
  • Lightweight Diffusion Layer from the Kth Root of the MDS Matrix
    Lightweight Diffusion Layer from the kth root of the MDS Matrix Souvik Kolay1, Debdeep Mukhopadhyay1 1Dept. of Computer Science and Engineering Indian Institute of Technology Kharagpur, India fsouvik1809,[email protected] Abstract. The Maximum Distance Separable (MDS) mapping, used in cryptog- raphy deploys complex Galois field multiplications, which consume lots of area in hardware, making it a costly primitive for lightweight cryptography. Recently in lightweight hash function: PHOTON, a matrix denoted as ‘Serial’, which re- quired less area for multiplication, has been multiplied 4 times to achieve a lightweight MDS mapping. But no efficient method has been proposed so far to synthesize such a serial matrix or to find the required number of repetitive multiplications needed to be performed for a given MDS mapping. In this pa- per, first we provide an generic algorithm to find out a low-cost matrix, which can be multiplied k times to obtain a given MDS mapping. Further, we optimize the algorithm for using in cryptography and show an explicit case study on the MDS mapping of the hash function PHOTON to obtain the ‘Serial’. The work also presents quite a few results which may be interesting for lightweight imple- mentation. Keywords: MDS Matrix, kth Root of a Matrix, Lightweight Diffusion Layer 1 Introduction With several resource constrained devices requiring support for cryptographic algo- rithms, the need for lightweight cryptography is imperative. Several block ciphers, like Kasumi[19], mCrypton[24], HIGHT[20], DESL and DESXL[23], CLEFIA[34], Present[8], Puffin[11], MIBS[22], KATAN[9], Klein[14], TWINE[36], LED[16], Pic- colo [33] etc and hash functions like PHOTON[33], SPONGENT[7], Quark [3] etc.
    [Show full text]
  • Variations to the Cryptographic Algorithms Aes and Twofish
    VARIATIONS TO THE CRYPTOGRAPHIC ALGORITHMS AES AND TWOFISH P. Freyre∗1, N. D´ıaz ∗ and O. Cuellar y2 ∗Faculty of Mathematics and Computer Science, University of Havana, Cuba. yFaculty of Mathematics, Physical and Computer Science, Central University of Las Villas, Cuba. 1e-mail: [email protected] 2e-mail: [email protected] Abstract The cryptographic algorithms AES and Twofish guarantee a high diffusion by the use of fixed 4×4 MDS matrices. In this article variations to the algorithms AES and Twofish are made. They allow that the process of cipher - decipher come true with MDS matrices selected randomly from the set of all MDS matrices with the use of proposed algorithm. A new key schedule with a high diffusion is designed for the algorithm AES. Besides proposed algorithm generate new S - box that depends of the key. Key words: Block Cipher, AES, Twofish, S - boxes, MDS matrix. 1 1 Introduction. The cryptographic algorithms Rijndael (see [DR99] and [DR02]) and Twofish (see [SKWHF98] and [GBS13]) were finalists of the contest to select the Advanced Encryption Standard (AES) convened by the National Institute of Standards and Technology from the United States (NIST). The contest finished in October 2000 with the selection of the algorithm Rijndael as the AES, stated algorithm was proposed by Joan Daemen and Vincent Rijmen from Belgium. In order to reach a high diffusion, the algorithms AES and Twofish, use a MDS (Maximal Distance Separable) matrices, selected a priori. In this article we will explain the variations of these algorithms, where the MDS matrices are selected randomly as function of the secret key.
    [Show full text]
  • On Constructions of MDS Matrices from Circulant-Like Matrices for Lightweight Cryptography
    On Constructions of MDS Matrices From Circulant-Like Matrices For Lightweight Cryptography Technical Report No. ASU/2014/1 Dated : 14th February, 2014 Kishan Chand Gupta Applied Statistics Unit Indian Statistical Institute 203, B. T. Road, Kolkata 700108, INDIA. [email protected] Indranil Ghosh Ray Applied Statistics Unit Indian Statistical Institute 203, B. T. Road, Kolkata 700108, INDIA. indranil [email protected] On Constructions of MDS Matrices From Circulant-Like Matrices For Lightweight Cryptography Kishan Chand Gupta and Indranil Ghosh Ray Applied Statistics Unit, Indian Statistical Institute. 203, B. T. Road, Kolkata 700108, INDIA. [email protected], indranil [email protected] Abstract. Maximum distance separable (MDS) matrices have applications not only in coding theory but are also of great importance in the design of block ciphers and hash functions. It is highly nontrivial to find MDS matrices which could be used in lightweight cryptography. In a SAC 2004 paper, Junod et. al. constructed a new class of efficient MDS matrices whose submatrices were circulant matrices and they coined the term circulating-like matrices for these new class of matrices which we rename as circulant-like matrices. In this paper we study this construction and propose efficient 4 × 4 and 8 × 8 circulant-like MDS matrices. We prove that such d × d circulant-like MDS matrices can not be involutory or orthogonal which are good for designing SPN networks. Although these matrices are efficient, but the inverse of such matrices are not guaranteed to be efficient. Towards this we design a new type of circulant- like MDS matrices which are by construction involutory.
    [Show full text]
  • On Constructions of MDS Matrices from Companion Matrices for Lightweight Cryptography
    On Constructions of MDS Matrices from Companion Matrices for Lightweight Cryptography Kishan Chand Gupta and Indranil Ghosh Ray Applied Statistics Unit, Indian Statistical Institute. 203, B. T. Road, Kolkata 700108, INDIA. [email protected], indranil [email protected] Abstract. Maximum distance separable (MDS) matrices have applications not only in coding theory but also are of great importance in the design of block ciphers and hash functions. It is highly nontrivial to find MDS matrices which could be used in lightweight cryptography. In a crypto 4 2011 paper, Guo et. al. proposed a new MDS matrix Serial(1; 2; 1; 4) over F28 . This representation has a compact hardware implementation of the AES MixColumn operation. No general study of d MDS properties of this newly introduced construction of the form Serial(z0; : : : ; zd−1) over F2n for arbitrary d and n is available in the literature. In this paper we study some properties of d MDS matrices and provide an insight of why Serial(z0; : : : ; zd−1) leads to an MDS matrix. For 2 efficient hardware implementation, we aim to restrict the values of zi's in f1; α; α ; α+1g, such that d Serial(z0; : : : ; zd−1) is MDS for d = 4 and 5, where α is the root of the constructing polynomial of F2n . We also propose more generic constructions of MDS matrices e.g. we construct lightweight 4 × 4 and 5 × 5 MDS matrices over F2n for all n ≥ 4. An algorithm is presented to check if a given matrix is MDS. The algorithm directly follows from the basic properties of MDS matrix and is easy to implement.
    [Show full text]
  • Building Efficient MDS Matrices
    Perfect Diffusion Primitives for Block Ciphers – Building Efficient MDS Matrices Pascal Junod and Serge Perfect Diffusion Primitives for Block Ciphers Vaudenay Preliminaries – Diffusion / Confusion Building Efficient MDS Matrices MDS Matrices ... Multipermutation ... and their Implementation Pascal Junod and Serge Vaudenay 32/64-bit Architectures 8-bit Architectures Bi-Regular Arrays Our Results Definition Some New Constructions (4; 4)-Multipermutation ÉCOLE POLYTECHNIQUE (8; 8)-Multipermutation FÉDÉRALE DE LAUSANNE Concluding Remarks Selected Areas in Cryptography '04 University of Waterloo (Canada), August 9, 2004 Perfect Diffusion Primitives Outline of this talk for Block Ciphers – Building Efficient MDS Matrices Pascal Junod and Serge Vaudenay Preliminaries Diffusion / Confusion MDS Matrices ... Multipermutation ... and their Implementation I Preliminaries 32/64-bit Architectures 8-bit Architectures I MDS Matrices ... Bi-Regular Arrays Our Results I ... and their Implementation Definition I Some New Constructions Bi-Regular Arrays (4; 4)-Multipermutation (8; 8)-Multipermutation I Some New Constructions Concluding Remarks Perfect Diffusion Primitives Back to Shannon for Block Ciphers – Building Efficient MDS Matrices Pascal Junod and Serge Vaudenay Preliminaries I Notions of confusion and diffusion introduced by Diffusion / Confusion MDS Matrices ... Shannon in “Communication Theory of Secrecy Multipermutation Systems” (1949) ... and their Implementation 32/64-bit Architectures I Confusion: “The method of confusion is to make the 8-bit Architectures
    [Show full text]
  • MDS Matrices with Lightweight Circuits
    MDS Matrices with Lightweight Circuits Sébastien Duval and Gaëtan Leurent Inria, France {sebastien.duval,gaetan.leurent}@inria.fr Abstract. MDS matrices are an important element for the design of block ciphers such as the AES. In recent years, there has been a lot of work on the construction of MDS matrices with a low implementation cost, in the context of lightweight cryptography. Most of the previous efforts focused on local optimization, constructing MDS matrices with coefficients that can be efficiently computed. In particular, this led toamatrix with a direct xor count of only 106, while a direct implementation of the MixColumn matrix of the AES requires 152 bitwise xors. More recently, techniques based on global optimization have been introduced, were the implementation can reuse some intermediate variables. In particular, Kranz et al. used optimization tools to a find good implementation from the description ofan MDS matrix. They have lowered the cost of implementing the MixColumn matrix to 97 bitwise xors, and proposed a new matrix with only 72 bitwise xors, the lowest cost known so far. In this work we propose a different approach to global optimization. Instead of looking for an optimized circuit of a given matrix, we run a search through a space of circuits, to find optimal circuits yielding MDS matrices. This results in MDS matrices with an even lower cost, with only 67 bitwise xors. Keywords: MDS matrix · lightweight cryptography 1 Introduction Since the 1990s, Substitution-Permutation Networks have been a prominent structure to build symmetric-key ciphers. These networks have been thoroughly studied and extensively instantiated, as in the current standard AES (Advanced Encryption Standard) [DR02].
    [Show full text]
  • Lightweight MDS Involution Matrices
    Lightweight MDS Involution Matrices Siang Meng Sim1, Khoongming Khoo2, Fr´ed´eriqueOggier1, and Thomas Peyrin1 1 Nanyang Technological University, Singapore 2 DSO National Laboratories, Singapore [email protected], [email protected], [email protected], [email protected] Abstract. In this article, we provide new methods to look for lightweight MDS matrices, and in particular involutory ones. By proving many new properties and equivalence classes for various MDS matrices construc- tions such as circulant, Hadamard, Cauchy and Hadamard-Cauchy, we exhibit new search algorithms that greatly reduce the search space and make lightweight MDS matrices of rather high dimension possible to find. We also explain why the choice of the irreducible polynomial might have a significant impact on the lightweightness, and in contrary to the classical belief, we show that the Hamming weight has no direct impact. Even though we focused our studies on involutory MDS matrices, we also obtained results for non-involutory MDS matrices. Overall, using Hadamard or Hadamard-Cauchy constructions, we provide the (involu- tory or non-involutory) MDS matrices with the least possible XOR gates for the classical dimensions 4 × 4, 8 × 8, 16 × 16 and 32 × 32 in GF(24) and GF(28). Compared to the best known matrices, some of our new candidates save up to 50% on the amount of XOR gates required for an hardware implementation. Finally, our work indicates that involutory MDS matrices are really interesting building blocks for designers as they can be implemented with almost the same number of XOR gates as non- involutory MDS matrices, the latter being usually non-lightweight when the inverse matrix is required.
    [Show full text]
  • Specification Ver
    MUGI Pseudorandom Number Generator Specification Ver. 1.2 Hitachi, Ltd. 2001. 12. 18 Copyright c 2001 Hitachi, Ltd. All rights reserved. MUGI SpecificationHitachi, Ltd. Contents 1 Introduction 1 2 Design Rationale 1 2.1 Panama-like keystream generator . ............... 2 2.2 Selectionof components ..................... 3 3 Preliminaries 4 3.1 Notations . .......................... 4 3.2 Data Structure .......................... 4 3.3 Finite Field GF(28)........................ 4 3.3.1 Data Expression ..................... 4 3.3.2 Addition .......................... 5 3.3.3 Multiplication ....................... 5 3.3.4 Inverse . .......................... 6 4 Specification 6 4.1 Outline ............................... 6 4.2Input................................ 7 4.3 Internal State . .......................... 7 4.3.1 State . .......................... 7 4.3.2 Buffer . .......................... 7 4.4 Update Function ......................... 8 4.4.1 Rho . .......................... 8 4.4.2 Lambda .......................... 9 4.5 Initialization . .......................... 9 4.6 Random Number Generation ................... 10 4.7 Components . .......................... 10 4.7.1 S-box . .......................... 11 4.7.2 Matrix . .......................... 11 4.7.3 F-function ......................... 12 4.7.4 Constants ......................... 13 5 Usage Notes 13 5.1 How to Use Keys and Initial Vectors .............. 13 5.2 Encryption and Decryption ................... 13 AS-box 15 B The multiplication table for 0x02 · x 16 C Test Vector 17 Copyright c 2001 Hitachi, Ltd. All rights reserved. MUGI SpecificationHitachi, Ltd. 1 Introduction This documentation gives a description of MUGI pseudorandom number generator. MUGI has two independent parameters. One is 128-bit secret key, and another is 128-bit initial vector. The initial vector can be public. The document is organized as follows: In Section 2 we show the de- sign rationale of MUGI. Next we give some notations and some fundamental knowledges inSection3.
    [Show full text]
  • LNCS 3017, Pp
    Improving Immunity of Feistel Ciphers against Differential Cryptanalysis by Using Multiple MDS Matrices Taizo Shirai and Kyoji Shibutani Ubiquitous Technology Laboratories, Sony Corporation 7-35 Kitashinagawa 6-chome, Shinagawa-ku, Tokyo, 141-0001 Japan {taizo.shirai,kyoji.shibutani}@jp.sony.com Abstract. A practical measure to estimate the immunity of block ci- phers against differential and linear attacks consists of finding the min- imum number of active S-Boxes, or a lower bound for this minimum number. The evaluation result of lower bounds of differentially active S-boxes of AES, Camellia (without FL/FL−1) and Feistel ciphers with an MDS based matrix of branch number 9, showed that the percentage of active S-boxes in Feistel ciphers is lower than in AES. The cause is a difference cancellation property which can occur at the XOR operation in the Feistel structure. In this paper we propose a new design strategy to avoid such difference cancellation by employing multiple MDS based matrices in the diffusion layer of the F-function. The effectiveness of the proposed method is confirmed by an experimental result showing that the percentage of active S-boxes of the newly designed Feistel cipher be- comes the same as for the AES. Keywords: MDS, Feistel cipher, active S-boxes, multiple MDS design 1 Introduction Throughout recent cryptographic primitive selection projects, such as AES, NESSIE and CRYPTREC projects, many types of symmetric key block ciphers have been selected for widely practical uses [16, 17, 18]. A highly regarded design strategy in a lot of well-known symmetric-key block ciphers consists in employ- ing small non-linear functions (S-box), and designing a linear diffusion layer to achieve a high value of the minimum number of active S-boxes [2, 4, 17, 18].
    [Show full text]
  • A New Involutory MDS Matrix for the AES
    International Journal of Network Security, Vol.9, No.2, PP.109–116, Sept. 2009 109 A New Involutory MDS Matrix for the AES Jorge Nakahara Jr and Elcio´ Abrah˜ao (Corresponding author: Jorge Nakahara Jr) Department of Informatics, UNISANTOS R. Dr. Carvalho de Mendon¸ca, 144, Santos, Brazil (Email: jorge [email protected]) (Received July 7, 2006; revised and accepted Nov. 8, 2006) Abstract SB(X)= AKi (MC (SR (SB(X)))), namely function com- position operates in right-to-left order. There is an input This paper proposes a new, large diffusion layer for the transformation, AK0 prior to the first round, and the last AES block cipher. This new layer replaces the ShiftRows round does not include MC. Further details about AES and MixColumns operations by a new involutory matrix components can be found in [14]. in every round. The objective is to provide complete diffu- This paper proposes a new diffusion layer for the AES sion in a single round, thus sharply improving the overall cipher, that replaces the original SR and MC layers. This cipher security. Moreover, the new matrix elements have new layer consists of a 16 × 16 involutory MDS matrix, low Hamming-weight in order to provide equally good per- denoted M16×16. The new design was called MDS-AES. formance for both the encryption and decryption opera- Thus, the new round structure of MDS-AES becomes AKi tions. We use the Cauchy matrix construction instead of ◦ M16×16 ◦ SB(X) = AKi (M16×16 (SB(X))). This de- circulant matrices such as in the AES.
    [Show full text]