F Functions Research Articles

Quantum generic attacks on key-alternating Feistel ciphers for shorter keys

Quantum generic attacks on key-alternating Feistel ciphers for shorter keys

An improved integral distinguisher scheme based on neural networks

At CRYPTO 2019, A. Gohr made a breakthrough in combining classical cryptanalysis and deep learning and applied his method to round reduced SPECK successfully. However, his suggested neural-based distinguisher scheme is only limited to differential cryptanalysis. In this paper, we have the following contributions: 1. We combine integral cryptanalysis and deep learning to propose our neural-based integral distinguisher scheme for the first time. To illustrate the effectiveness of our distinguisher scheme, we apply it to block ciphers of different structures, such as substitution-permutation structure ciphers (PRESENT and RECTANGLE), Feistel structure cipher (LBLOCK), and add-rotate-XOR cipher (SPECK) and compare the results with the state-of-the-art classical integral distinguishing method, namely, the bit-based division property. To our great surprise, our neural network-based integral distinguisher can extend the number of distinguished rounds for all block ciphers by two additional rounds (except RECTANGLE, where it is improved by one round) under the same data complexity. 2. As an additional advantage of our scheme, we demonstrate that our Neural Distinguisher (ND) is not only helpful for block cipher designers but also can assist attackers to mount key recovery attacks. To this end, we show how to exploit our ND to mount a key recovery attack and apply it to SPECK32/64. Out of the 1000 trials of key recovery attacks with different keys in 45% of cases, the first suggested subkey is exactly the real subkey of the last round of the cipher. For the remaining 55%, the second or third suggested subkey is exactly the real subkey of the last round of the cipher. 3. To have a piece of concrete evidence for the advantage of our scheme over classical integral methods, we design an experiment known as the same-difference experiment. In this experiment, we show that our ND can learn some features beyond the capabilities of classical integral methods. We then propose a set of features that can justify the gap between classical integral methods and our neural-based integral distinguisher and verify them by further experiments.

Security evaluation on type‐1 and type‐1‐like 4‐branch generalized Feistel structures and application to reduced‐round Lesamnta‐LW‐BC

Generalized Feistel structures (called GFSs for short) are one of the most popular block cipher structures. They are mainly divided into type-1, type-2 and type-3 GFS. Among them, type-1 and type-1-like ones attracted much attention during the past decades because of the simple design and high implementation efficiency. In this paper, the security of the type-1 and type-1-like 4-branch GFS with substitution permutation round functions against the impossible differential attack are evaluated. For these two structures, 21-round impossible differential distinguishers are constructed when the linear layers P satisfy γ(P) ≥ 2, where γ(P) denotes the primitive index of P. Especially, when γ(P) = 2, the 21-round distinguisher of the type-1 structure is one round longer than before. Furthermore, for a specific block cipher Lesamnta-LW-BC, which takes the type-1-like structure, by exploiting the details of the linear layer, a better 21-round impossible differential distinguisher is constructed, which contains more impossible differentials than before. With this distinguisher, a 27-round impossible differential attack on Lesamnta-LW-BC is performed. The length of this attack is 8 rounds longer than the previous best one. Our results can provide guidance for designing and analysing the type-1 and type-1-like GFS as well as the specific block ciphers which take the structures.

Single Feistel lapse acting on reduced ASCII codes followed by a genetic crossover

This article describes a new cryptosystem that incorporates the most powerful genetic operators. With the aim of better integration in the field of color image encryption security, this technique starts with the application of an advanced Feistel scheme and ends with the implementation of deeply modified genetic operators. After vectorization of the original image, an application of the advanced Feistel scheme on blocks of random size will be launched. The output vector is transcribed in restricted ASCII code to achieve a genetic cross suitable for the encryption of color images. The output vector obtained is transcribed in restricted ASCII code to considerably improve the effects of the genetic crossing. This step increases the impact of the avalanche effect and protects the system from differential attacks. Simulations performed on a large volume of images of different sizes and formats ensure that our approach is not exposed to known attacks.Article HighlightsThe one Feistel rounds in our algorithm represent a large modification of a classical scheme. The main new features are:First Feistel lap and Cross-over genetic operator.Switching to ASCII code.Genetic crossover arrangement.

Weak Tweak-Keys for the CRAFT Block Cipher

CRAFT is a lightweight tweakable Substitution-Permutation-Network (SPN) block cipher optimized for efficient protection of its implementations against Differential Fault Analysis (DFA) attacks. In this paper, we present an equivalent description of CRAFT up to a simple mapping on the plaintext, ciphertext and round tweakeys. We show that the new representation, for a sub-class of keys, leads to a new structure which is a Feistel network, with non-linear operation and key addition only on half the state. Consequently, it reveals a class of weak keys for which CRAFT is less resistant against differential and linear cryptanalyses. As a result, we present one weak-key single-tweak differential attack on 23 rounds (with time complexity of 294 encryptions and data complexity of 274 chosen plaintext/tweak/ciphertext tuples and works for 2112 weak keys) and one weak-key related-tweak attack on 26 rounds of the cipher (with time complexity of 2105 encryptions and data complexity 273 chosen plaintext/tweak/ciphertext tuples and works for 2108 weak keys). Note that these attacks do not break the security claim of the CRAFT block cipher.

Design of a Linear Layer for a Block Cipher Based on Type-2 Generalized Feistel Network with 32 Branches

Design of a Linear Layer for a Block Cipher Based on Type-2 Generalized Feistel Network with 32 Branches

A symmetric DNA encryption process with a biotechnical hardware

The growing rate of internet/network technologies day by day dramatically increases the formation of data in the world. As the flow of information increases on the network, time security threats are also increasing for users. In order to protect data, cryptography and steganography have been used from the past to the present. The goal of cryptography is to transfer the message between sender and receiver in a way that is incomprehensible to the observer. Nowadays, DNA cryptography is a shining branch in the field of cryptography. The primary purpose here is to employ DNA as a carrier and to employ modern biological techniques as application tools. In this study, a DNA cryptography technique was proposed by integrating DNA encoding and DNA operators into the Feistel network structure. Here, DNA itself was used as a carrier instead of traditional digital media such as image, text or video, while its biological tools were being used as implementation tools. Besides, the developed simulation software and the synthesized DNA sequence were digitally and biologically integrated into specifically created biotechnical hardware. Experimental results demonstrated that the proposed study has efficient outcomes for cryptographic requirements; capacity of nearly 100%, brute force attack nearly 12 × 106 years for only one block, key space that is 280 for only one block, and entropy analyses close to 2. Besides, the implementation of the proposed method has been verified by vitro experiments.

FPGA implementation of a chaos-based image encryption algorithm

With the rapid development of communication networks and the establishment of 5G networks, there is a growing demand for the transmission of images and videos with different sizes and formats. Since these can contain sensitive and personal information, security is of great importance when transferring the contents of such files. Therefore, the use of powerful encryption mechanisms is an absolute requirement to protect the confidentiality of the exchanged data. In this study, we propose an image encryption algorithm with a high level of security. Thus, a chaotic system is proposed, and its state variables have been used to create a new substitution matrix. The importance of this matrix lies both in its use to generate encryption keys and in the encryption algorithm itself. In formulating the proposed encryption algorithm, we adopted the Feistel network in addition to some steps of the Advanced Encryption Standard (AES). The results of the various tests prove that the proposed algorithm guarantees high resistance to statistical and differential attacks and can therefore be used safely in image encryption. The incorporation of various algorithms suggested in this article in the form of IPcore for FPGA platforms amply promotes the use of our cryptosystem in various embedded systems or IoT environments.

New Genetic Operators for Developing S-Boxes With Low Boomerang Uniformity

The boomerang uniformity measures the resistance of block ciphers to boomerang attacks and has become an essential criterion of the substitution box (S-box). However, the S-box es created by the Feistel structure have a poor property of boomerang uniformity. The genetic algorithm is introduced to improve the properties of the S-box es created by the Feistel structure. New genetic operators are designed for the genetic algorithm to improve its searchability. The new genetic algorithm generates some 8 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 8 bijective S-boxes with differential uniformity 6, nonlinearity 108, and boomerang uniformity 10, which has dramatically improved the properties of the S-boxes created by the Feistel structure. Furthermore, the new genetic algorithm also improves the properties of the S-box population created by the Feistel structure as a whole. We compare the S-boxes generated by the new genetic algorithm with those generated by the traditional one. The comparison results show that the S-boxes generated by the new genetic algorithm have better properties than the S-boxes generated by the traditional genetic algorithm, demonstrating the new genetic algorithm’s effectiveness and superiority in developing S-boxes.

Cryptographic symmetric structures based on quasigroups

In our paper we study the effect of changing the commutative group operation used in Feistel and Lai-Massey symmetric structures into a quasigroup operation. We prove that if the quasigroup operation is isotopic with a group the complexity of mounting a differential attack against our generalization of the Feistel structure is the same as attacking the unkeyed version of the general Feistel iteration based on Also, when is non-commutative, we show that both versions of the Feistel structure are equivalent from a differential point of view. For the Lai-Massey structure, we introduce four non-commutative versions, we argue for the necessity of working over a group and we provide some necessary conditions for the differential equivalency of the four notions.

A quantum image encryption algorithm based on the Feistel structure

A quantum image encryption algorithm based on the Feistel structure

SCENERY: a lightweight block cipher based on Feistel structure

SCENERY: a lightweight block cipher based on Feistel structure

Quantum Differential Collision Distinguishing Attacks on Feistel Schemes

Feistel schemes are important components of symmetric ciphers, which have been extensively studied in the classical setting. We examine the extension methods of differential distinguishers of Feistel key-function and Feistel function-key schemes. The schemes are subjected to quantum differential collision distinguishing attacks based on the methods. The results show that the complexity is lower than that of differential attacks using only Grover algorithm, and the complexity of differential collision attack based on the Brassard-Høyer-Tapp and Grover algorithms is lower than that of quantization when using only the Grover algorithm. The results also show that different algorithms and methods can be combined to produce a more effective cryptanalysis approach. This provides a research direction for post-quantum cryptographic analysis and design.

An Enhanced Hybrid Watermarking Method and Imaging System for Securing Medical Images

Medical image processing typically deals with the exploration of several medical image datasets for attaining an effective solution in diagnosing the affected patients. Medical image of the patients are typically stored in digital form as Electronic patient’s record (EPR), which must be dealt with utmost security and confidentiality, as the patient’s data are linked with external open platforms for future diagnosis. Medical image watermarking and encryption schemes assist in meeting the above requirements in effectively securing the patient’s image data. The ultimate objective of this research inclines towards securing medical images so as to achieve maximum effectiveness over health related areas. In this paper, an enhanced hybrid medical image watermarking and equivalent encryption strategy is typically investigated for attaining an effective solution towards medical image processing. The proposed methodology works with the integration of image watermarking algorithm together with an encryption algorithm. Image watermarking is achieved by a system based on Redundant discrete wavelet transform and Singular value decomposition. Moreover, by utilizing the property of chaotic signals for improving the integrity, a hybrid medical image watermarking technique is proposed by upgrading the Arnold cat map (ACM) with Logistic map. For image encryption, Symmetric block encryption algorithm based on Feistel structure is proposed. The efficiency of the proposed strategy is estimated in terms of Peak signal to noise ratio (PSNR), Mean square error (MSE) and Correlation coefficient (CC).

Implementasi Algoritma Adaptive Huffman Code Dalam Kompresi File Teks Terenkripsi Algoritma Loki97

Data security and confidentiality is one of the most important aspects in today's information systems. Due to the rapid development of science and technology that allows the emergence of new techniques, which are misused by certain parties that threaten the security of the information system. The fall of information into the hands of other parties can cause harm to the owner of the information. Therefore we need a way that can provide security for the data, one of which is using cryptographic techniques. Cryptography technique is a science or art in fulfilling security aspects in communicating by changing the content of information into incomprehensible information. One of the algorithms that can be used is the Loki97 algorithm, which is a cryptographic algorithm that uses the Feistel network system. The process carried out in this study is to first encrypt the text file using the Loki97 algorithm, then the results of the encrypted file will be compressed using the Adaptive Huffman Code algorithm, resulting in an encrypted and compressed file.

Extended of TEA: A 256 bits block cipher algorithm for image encryption

&lt;p&gt;This paper introduces an effective image encryption approach that merges a chaotic map and polynomial with a block cipher. According to this scheme, there are three levels of encryption. In the first level, pixel positions of the image are scuffled into blocks randomly based on a chaotic map. In the second level, the polynomials are constructed by taking N unused pixels from the permuted blocks as polynomial coefficients. Finally, the third level a proposed secret-key block cipher called extended of tiny encryption algorithm (ETEA) is used. The proposed ETEA algorithm increased the block size from 64-bit to 256-bit by using F-function in type three Feistel network design. The key schedule generation is very straightforward through admixture the entire major subjects in the identical manner for every round. The proposed ETEA algorithm is word-oriented, where wholly internal operations are executed on words of 32 bits. So, it is possible to efficiently implement the proposed algorithm on smart cards. The results of the experimental demonstration that the proposed encryption algorithm for all methods are efficient and have high security features through statistical analysis using histograms, correlation, entropy, randomness tests, and the avalanche effect.&lt;/p&gt;

New Approach towards Generalizing Feistel Networks and Its Provable Security

This paper proposes a new approach to generalizing Feistel networks, which unifies the classical (balanced) Feistel network and the Lai–Massey structure. We call the new structure extended Feistel (E-Feistel) network. To justify its soundness, we investigate its indistinguishability using Patarin’s H-coefficient technique. As a result, it is proved that the 4-round key-alternating E-Feistel (KAEF) cipher with adequately derived keys and identical round functions is secure up to 2 n / 2 queries, i.e., birthday-bound security. In addition, when adjacent round keys are independent and independent round functions are used, the 6-round KAEF is secure up to beyond-birthday-bound 2 2 n / 3 queries. Our results indicate that the E-Feistel structure is secure and reliable and can be adopted in designing practical block ciphers.

On the (im)possibility of improving the round diffusion of generalized Feistel structures

Generalized Feistel structures (GFS) are widely employed as the underlying structure of primitives like block ciphers and hash functions. In order to improve its slow diffusion, several design ideas have been proposed. In this contribution, we explore the (im)possibility of further improving the round diffusion of GFS by modifying its round permutations. First, we generalize a technique called sub-block dividing, which further divides each sub-block into smaller blocks. We prove that the diffusion round of a round permutation with sub-block dividing is four, regardless of the number of sub-blocks. Moreover, we show that the round diffusion of GFS can be improved by alternately using two different round permutations instead of a single permutation. We present the first results that, by using two round permutations, 10- and 12-block GFS partially and fully reach the lower bounds on the diffusion round, respectively.

Integral and impossible‐differential attacks on the reduced‐round Lesamnta‐LW‐BC

Lesamnta-LW-BC is the internal block cipher of the Lesamnta-LW lightweight hash function, specified in ISO/IEC 29192-5:2016. It is based on the unbalanced Feistel network and Advanced Encryption Standard round function. In this study, the security of Lesamnta-LW-BC against integral and impossible-differential attacks is evaluated. Specifically, the authors searched for the integral distinguishers and impossible differentials with Mixed-Integer Linear Programming-based methods. As a result, the discovered impossible differential can reach up to 21 rounds, while three integral distinguishers reaching 18, 19 and 25 rounds are obtained, respectively. Moreover, it is also feasible to construct a 47-round integral distinguisher in the known-key setting. Finally, a 20-round key-recovery attack is proposed based on the discovered 18-round integral distinguisher and a 19-round key-recovery attack using a 17-round impossible differential. To the best of the authors' knowledge, this is the first third-party cryptanalysis of Lesamnta-LW-BC.

Improved indifferentiability security proof for 3-round tweakable Luby–Rackoff

Improved indifferentiability security proof for 3-round tweakable Luby–Rackoff