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Block permutation and Co-XOR (BPCX) image encryption is a commonly used encryption method for reversible data hiding in the encryption domain, which can effectively improve the embedded capacity and the ability resisting the existing attacks including ciphertext-only attack and known plaintext attack (KPA). This paper proposes a KPA based on bit-block inversion and mean equivalent division (MED) to estimate the block permutation key of BPCX image encryption. Firstly, we divide an image block into the bit-block and point out that the maximum of the numbers of 0 bit and 1 bit of a bit-block before and after the Co-XOR encryption remains unchanged. And then two inversion rules of bit-block are defined to construct pseudo plain-ciphertext images to eliminate the influence of pixel value changes caused by Co-XOR encryption. Finally, the MED based KPA is designed to estimate the block permutation key sequence according to the pseudo plain-ciphertext images. The relationship between the key estimation accuracy and the number of known plain-ciphertext pairs, block size, and pseudo ciphertext are discussed. Experimental results show that even in the minimum block size (2×2), the average estimated correct rate of the block permutation sequence exceeds 40%. The block permutation key estimation accuracy is more than 50% when the block size is greater than 3×3. Some improved encryption methods against the proposed KPA are also given.

Reversible data hiding in encrypted images (RDH-EI) technology is commonly used in cloud storage images for privacy protection. Most existing RDH-EI techniques reported in the literature applied block permutation and co-modulation (BPCM) encryption to generate encrypted images. This work analyses the security of the RDH-EI algorithm based on BPCM encryption under known plaintext attack (KPA). Different from the existing KPAs, this paper considers that attackers can perform KPA based on marked encrypted images and shows that BPCM encryption has the risk of information leakage. To find the constant features of a block before and after co-modulation, the first-pixel difference block (FDB) of a block is first defined. Then, a pseudo cypher difference image of the cyphertext image is constructed to eliminate the changed FDBs so that the differences in the cyphertext FDBs are the same as the FDBs in the corresponding plaintext difference image. Finally, we design an FDB-based block permutation key estimation method according to the plaintext difference image and pseudo cyphertext difference image. The influence of block size on key estimation accuracy and the time complexity of the proposed KPA algorithm are analysed and discussed. Experimental results show that the correct rate of key estimation is positively correlated with the block size and the number of plain-cyphertext pairs. The average correct rate of key estimation reaches 63% when the block size is greater than 33.

In current world security of the wired and remote organization is something essential. Organization security is a significant part of data sharing. Many groundbreaking executions and security approaches have been developed for this purpose. The knowledge measure, which has been transferred, is not a factor. The main factor is, how much protection the channel offers during information transmission. One system of this kind allows safe transmission of information without losing its classification and honesty Cryptography. The open design and dynamic geography combined with absence of foundation make remote organizations helpless against assortment of assaults. The different kinds of assaults can conceivable on wired and remote organizations, for example, Cipher text assaults, Brute power assaults, Known plaintext assaults, Denial of administration assaults, Side channel assaults and so forth. These kinds of assaults can be forestalled by actualizing different cryptographic procedures to give security to client information. This paper presents is to present the idea of Cryptography, History of Cryptography, Modern Cryptography. This exploration zeroed in on various sorts of cryptography calculations that exist, as AES, DES, 3DES, IDEA, RSA, ECC, Homomorphic and Blowfish and so forth.

To satisfy requirements of high security and transmission efficiency in application scenarios with high image quality, an image lossless encryption and compression algorithm based on four-dimensional hyperchaos and embedded block coding with optimal truncation (EBCOT) is proposed in this paper. First, according to a character that the amplitude of the high-frequency part of the wavelet coefficient is less than the amplitude of the low-frequency part, an encryption algorithm for the wavelet coefficients is proposed to improve the security while reducing the impact on the compression performance. Second, the bit-plane coding and arithmetic coding in EBCOT Tier1 are embedded with encryption points, and the encryption process and compression process are combined to propose a secure EBCOT Tier1 code, which could further improve the security of the algorithm. Furthermore, this paper proposes a new four-dimensional hyperchaotic system, using Secure Hash Algorithm-256 (SHA-256) to generate initial values of the chaotic system, so that the algorithm could resist known plaintext and selected plaintext attacks. The results of the mean square error of all restored images are 0 and the information entropy of this algorithm is close to the theoretical value. The experimental results show that the algorithm has high security and lossless compression performance.

A novel image steganography technique in order to hide the ciphered voice data has been suggested in this work. The doctor's voice comments belonging to a coronavirus disease 2019 (COVID-19) patient are hidden in a medical image in order to protect the patient information. The introduced steganography technique is based on chaos theory. Firstly, the voice comments of the doctor are converted to an image and secondly, they are ciphered utilizing the suggested encryption algorithm based on a chaotic system. Then, they are embedded into the cover medical image. A lung angiography dual-energy computed tomography (CT) scan of a COVID-19 patient is used as a cover object. Numerical and security analyses of steganography method have been performed in MATLAB environment. The similarity metrics are calculated for R, G, B components of cover image and stego image as visual quality analysis metrics to examine the performance of the introduced steganography procedure. For a 512 x 512 pixel cover image, SSIM values are obtained as 0.8337, 0.7926, and 0.9273 for R, G, B components, respectively. Moreover, security analyses which are differential attack, histogram, information entropy, correlation of neighboring pixels and the initial condition sensitivity are carried out. The information entropy is calculated as 7.9993 bits utilizing the suggested steganography scheme. The mean value of the ten UACI and NPCR values are obtained as 33.5688% and 99.8069%, respectively. The results of security analysis have revealed that the presented steganography procedure is able to resist statistical attacks and the chaotic system-based steganography scheme shows the characteristics of the sensitive dependence on the initial condition and the secret key. The proposed steganography method which is based on a chaotic system has superior performance in terms of being robust against differential attack and hiding encrypted voice comments of the doctor. Moreover, the introduced algorithm is also resistant against exhaustive, known plaintext, and chosen plaintext attacks.

To protect image information security, we propose an encryption algorithm based on chaotic sequences and bits' cross-diffusion. First, two chaotic sequences are generated by two-dimensional logic-sine coupling mapping, and the original image is scrambled with the two sequences. Secondly, the scrambled image is transformed into a one-dimensional sequence, and the low-order bits between every two pixels are fused to change the detailed information of the image, improved the ability to resist differential attacks. Finally, chaotic sequences are generated by iterative logical mapping to perform pixel replacement and ciphertext diffusion. The known plaintext attack can be effectively resisted because of the stochastic combination of diffusion scheme and chaotic sequence. It also has a significant effect on resisting differential attack. Take Lena image as an example, NPCR and UACI can reach 99.6063% and 33.4477%, respectively, which are very close to the ideal value. The encryption scheme has good key sensitivity and strong ability to resist statistical attacks, which shows that the algorithm has adequate security.

In this paper, we concretely formulate to derive the attacker's success probability of obtaining the shared secret keys for the Y00 protocol under a combination of a quantum collective attack with infinitely-long known-plaintext, naming it “collective known-plaintext attack” in this work. In contrast, our previous work showed only the necessary condition to design Y00 transmitters to be information-theoretic secure. The keystone of the security evaluations in this work is the time-translational symmetry of the Y00 signals modulated by pseudo-random number generators, such as linear-feedback shift registers or Mersenne twisters. With the assist of a true-random deliberate-signal-randomization, information-theoretic security would be realized. By numerical simulations, we can determine whether the designed Y00 transmitters are information-theoretic secure. However, this work's security evaluation may not apply to the transmitters with cryptographically-secure pseudo-random number generators because they might not have time-translational symmetry, even though such Y00 transmitters may be securer. We also describe future challenges for theorists to accelerate designing securer Y00 transmitters.

Many encryption algorithms are designed to decrease the probability of cyberattacks by assuring data security as well as system and participant authentication. However, in the development of computer resources cryptanalytical techniques have been developed and performed competitively in information security with good results. In this paper, we reported security flaws in the recently offered encryption technique based on a chaotic map for Internet of Health Things (IoHT) security. The scheme was based on a new chaotic map, modified Mandelbrot set, and conditional shift algorithm asserting the encryption algorithm is secure. We have performed some cryptographic attacks to retrieve the key from the understudy cryptosystem. The key was retrieved in little computation by using a chosen-plaintext attack and one known plaintext ciphertext pair. The minimum execution time of performed attacks indicates the vulnerability of the diffusion-based encryption algorithm. To enhance the security of the understudy cryptographic algorithm, we have also suggested certain improvements.

To contend with the growing concern of information security, firms are espousing cryptography for protection. To comprehend this need, the paper proposes a block cipher that ensures confidentiality and secrecy for secure data communication network. A high-quality cryptographic process ensures high entropy, high key sensitivity, ability to resist known plaintext and chosen-plaintext attack, high speed of execution, high key space, high randomness and resistance towards differential attack. In projected work, encryption mechanism is comprises of multiple processes and each process is devised key dependent utilizing diverse keys to ensure high key sensitivity and vast resistance power towards differential attack. The keys are generated using contemporary encryption process- the quantum chaotic map due to its high randomness and non periodicity, which includes confusion and diffusion processes. For the confusion process, Electronic Code Book (ECB), Initial Permutation (IP), Bit plane scrambling, and Inter bit plane scrambling are employed. The ECB and IP, being matching processes are chosen for high speed of execution. Bit level permutation unlike byte level is applied to reinforce randomness, in conjunction with variable number of rounds as per the security key. For diffusion process, the folding technique is used along eight directions, exploiting different keys. To reveal the efficacy of the proposed methodology, it is compared with the existing renowned methods on the basis of Cryptanalysis, Perceptibility analysis, Statistical analysis, etc. It is asserted that results such as differential attack, cryptanalysis, and key space analysis are reasonably enhanced than others while entropy and speed of execution are at equivalence with other techniques.

In order to improve the security of reversible data hiding algorithm in encrypted images, Liu designed an image multi-permutation encryption algorithm. By combining bit-plane permutation with pixel-block permutation, the embedding capacity of the algorithm is improved, and the ability of the encryption algorithm to resist existing Ciphertext-Only and Known-Plaintext attack is effectively improved. To analyze the security performance of the encryption algorithm, a Known-plaintext attack method based on the Root Mean Square(RMS) of image block is proposed in this paper. Firstly, the permutation order of bit plane is estimated by using the invariant distribution ratio of 0 and 1 before and after image encryption, the original pixel values is restored. Then, according to the characteristics that the pixel values of the image remain unchanged during block permutation and intra-block pixel permutation, the image block RMS feature is defined to search and estimate the block permutation sequence. Image block RMS equivalence class is defined by the image block RMS value, the ratio of the maximum number of elements in the equivalence class to the total number of pixels is p, which determines the difficulty of known plaintext attack. For the common image test set, 96% of the images have a p-value of less than 0.1, and only 4% of the images have a p-value greater than 0.1. Experimental results show that, When p 0.1, the attacker can crack more than 80% of the image content by two pairs of plaintext and ciphertext.

There has been a surge of interests in the security of cyber-physical systems (CPSs), yet it is commonly assumed that the adversary has a full knowledge of physical system models. This paper argues that such an unrealistic assumption can be relaxed: the adversary might still be able to identify the system model by passively observing the control input and sensory data. In such a setup, the attack with knowledge of input-output data can be categorized as a Known-Plaintext Attack. A necessary and sufficient condition has been provided, under which the adversary can uniquely obtain the knowledge of the underlying physical system. From the defenders perspective, a secure controller design—which exhibits a low rank structure—is proposed which renders the system unidentifiable to the adversary, while trading off the control systems performance. Finally, a numerical example has been provided to demonstrate the effectiveness of the proposed secure controller design.

Genetic algorithm, a technique inspired by evolutionary biology to mimic the process of natural selection, has been applied in the image encryption due to the confusion and diffusion properties of mutation and crossover processes involved in the genetic algorithm. In this paper, we analyze the security of the image encryption designed based on genetic algorithms. We perform a known plaintext attack on Biswas et al. image encryption scheme designed based on chaotic maps and genetic algorithms. We show that the encryption scheme is not as secure as claimed by Biswas et al. since the proposed attack reduces the claimed 448-bit security to 264.28-bit security. The proposed attack and its analysis can be utilized and extended to other image encryption schemes designed based on genetic algorithms.

Based on chaotic encryption technology and DNA cryptography, a multidimensional chaotic image encryption algorithm based on DNA coding is proposed in this paper. Firstly, the MD5 algorithm is used to extract the features of the image, generate a new key in association with the user key, and then encode the original image in DNA. The traditional three-dimensional Lorenz system is improved to form a four-dimensional hyperchaotic Lorenz system. According to the principle of DNA cryptography, a series of operations such as scrambling, mutation, DNA addition and DNA XOR are performed on the DNA coding sequence, and finally decoded to obtain a password image. Key space analysis, statistical analysis, known plaintext attack analysis and experimental results show that the algorithm has better image encryption performance and ability to resist various common attacks.

A novel image authentication scheme based on two level phase retrieval algorithm (PRA) propagated in fractional Hartley transform (FrHT) to extract two phase-only masks (POMs) is proposed. PRA is based on iterative phase mask which uses nonlinear process to generate POMs which in turn makes the system immune to chosen plaintext attack (CPA) and known plaintext attack (KPA). Random amplitude mask (RAM) and random phase mask (RPM) are used as encryption keys which makes the system immune to special attack. Further multiple level of security leads to the achievement of non-convergence of MSE and good performance in the retrieval process. Apart from encrypting the information, authentication has also been included in the scheme. The features incorporated in any plaintext have been shown to provide unique signatures, which can be used to verify their authenticity. The content of the original images can be authenticated only if the authentication key is correct. The robustness of the proposed multiple level cryptosystem has been examined based on various parameters by simulating on MATLAB 9.4.0 (R2018a). The experimental results highlight the suitability and shows the attacker cannot recover the original image without the knowledge of POMs. The scheme has also been compared with similar algorithms which proves that the proposed two-level scheme is more secure, feasible and effective.

Bu tez çalışmasında 2019 yılında C. Flaut tarafından fark denklemleri kullanılarak tanımlanan şifreleme algoritması ayrıntılı olarak ele alınmıştır ve bu algoritmanın güvenlik analizi yapılmıştır. Şifreleme sistemlerinin güvenirliğini test etmek için yapılan saldırı yöntemlerinden biri olan “Bilinen Açık Metin Saldırısı” belirli uzunluktaki açık metin ve kapalı metin çifti kullanılarak anahtarı bulma işlemine dayanır. Bu tez çalışmasında C. Flaut tarafından önerilen şifreleme algoritmasının güvenirliği bilinen açık metin saldırısı ile test edilmiştir ve algoritmanın bu saldırı yöntemi ile kırılabildiği gösterilmiştir. Bu saldırı yönteminde açık metin-kapalı metin çifti arasındaki bağlantı kullanılarak yeterli sayıda denklemden oluşan lineer denklem sistemi oluşturulmuştur ve bu sistem Gauss eliminasyon yöntemiyle çözülerek şifrelemede kullanılan gizli anahtar ele geçirilmiştir. Böylece bu şifreleme sisteminin bilinen açık metin saldırısına karşı güvensiz olduğu gösterilmiştir, In this thesis, an encryption algorithm based on the difference equations proposed by C. Flaut (2019) is discussed in detail and its security analysis is performed. One of the attack methods used to test the reliability of encryption systems, "known-plaintext attack", is based on finding the key using a certain length of known plaintext and ciphertext pairs. In this thesis, the reliability of the encryption algorithm proposed by Flaut (2019) is tested by applying the known-plaintext attack, and it is observed that the algorithm can be broken with this attack. In this attack, a linear equation system that has sufficiently linear equations is formed from the connection between the plaintext-ciphertext pairs. Thus, by solving this linear equation system with the Gaussian elimination method, the secret key of the encryption algorithm is obtained, which approves that this encryption system is insecure against the known-plaintext attacks.

Lightweight DES Algorithm (DESL) was introduced by Axel Poschmann et.al as a strong, compact and efficient encryption algorithm suitable for constraint resource like WSNs, RFID and IOT devices. This paper discusses the security of the DESL against Linear Cryptanalysis which is a known plaintext attack in which a large number of plaintext-ciphertext pairs are used to determine the value of key bits. Linear cryptanalysis works on the principle of finding “high probability occurrences of linear expressions involving plaintext bits, ciphertext bits, and subkey bits”. Furthermore, we show that DESL is more resistant against the linear cryptanalysis attack than classical DES.

In this study, a novel asymmetric image encryption scheme based on the Rivest-Shamir-Adleman (RSA) algorithm and Arnold transformation is proposed. First, the asymmetric public key RSA algorithm is used to generate the initial values for a quantum logistic map. Second, the parameters of the Arnold map are calculated. Then, Arnold scrambling operation is performed on the plain image to achieve the rough hiding of image information. Third, each row and each column of the image are taken as different units respectively and then exclusive-OR (XOR) diffusion is applied. Finally, the generated keystream is used to perform an end-to-start cyclic modulo diffusion operation for all rows and columns to produce the final cipher image. In addition, the keystream is related to the plain image, which can enhance the ability to resist chosen plaintext attack and known plaintext attack. The test results also show that the proposed encryption algorithm has strong plain sensitivity and key sensitivity.

The chaotic natures of a new fractal dynamical system have been investigated experimentally and used to yield chaotic sequences to design cryptosystems. An adaptive permutation-diffusion mechanism is introduced to achieve strong resistance against chosen/known plaintext attacks. Plain image related chaotic sequences are generated to shuffle the positions of pixels in the permutation stage. In the diffusion process, DNA coding, decoding operations and diffusion function are proposed to alter the pixels' gray values. The security and performance analysis, such as histogram analysis, correlation analysis, entropy analysis, differential analysis, have been done. The simulation results show that the proposed cryptosystem is secure enough for practical application.

Aiming at the problem that the encryption structure of some image encryption algorithms had nothing to do with the plaintext and cannot guarantee the security of the ciphertext image, this paper proposed an image encryption algorithm based on a four-dimensional hyperchaotic system. The initial value of the chaotic system is determined by the SHA256 hash value of the plaintext image and the input parameters, making the algorithm capable of resisting known plaintext attacks and selected plaintext attacks. At the same time, the hash value and input parameters are used to determine the moving step size of the Zigzag scrambling algorithm. The algorithm uses the CFB mode in block ciphers, and updates the chaotic sequence according to the ciphertext, which makes the subscript selection of the Knuth algorithm more random to improve the encryption performance of this algorithm. The experimental results demonstrate the excellent robustness and security of the proposed scheme. It can resist common attack methods such as statistical analysis and differential attacks.

The sculpture “Kryptos” at the Central Intelligence Agency in Langley, Virginia, contains four encrypted passages. The last, known as “K4” and consisting of 97 letters, remains unsolved. In this work, we look at unusual statistical properties of the K4 ciphertext, together with the known plaintext, using Monte Carlo sampling to perform permutation testing. This provides evidence strongly indicating a definite “one-to-one” relationship between corresponding plaintext and ciphertext letters. It also points toward a possible encryption method which could account for most or all of the observed properties. This is the “Gromark” cipher invented by Hall (1969, 1975) and analyzed by Blackman (1989).

This paper presents a k-shuffle based audio scrambling technique which yields cipher audio with varying audibility that is useful in perceptual video encryption algorithms. In this technique the encryption and decryption algorithms group the input audio signals into m-piles of n-values each. The encryption procedure retains the first signal value (of the first pile) and the last signal value (of the last pile) in their respective positions while re-arranging the rest by taking in turns, the 1st values of each of the m-piles, then the 2nd values, up to the nth values. At the receivers end, the decryption algorithm re-orders the scrambled audio signals back in to their respective original positions using the reverse of the k-shuffle technique. It is shown that, the audibility of the cipher audio is controlled by varying the number of piles. The performance of the proposed technique is demonstrated by simulations. The results of the simulations show that the proposed technique offers some level of resistance to chosen/known plaintext attacks.

In this paper, we propose a new two-dimensional Sine improved Logistic iterative chaotic map with infinite collapse (ICMIC) modulation map (2D-SLIM) based on the improved two-dimensional closed-loop modulation coupling model. The performance analysis results show that it has a large parameter space, large Lyapunov exponents and high complexity. Combining this map with compressive sensing, a fast image encryption algorithm is proposed. In this algorithm, a plain image is measured by two circular measurement matrices from two directions, and then the image is re-encrypted by employing the row and column encryption to simultaneously achieve permutation and diffusion. In addition, the SHA-512 hash values of the plain image are generated to calculate the initial conditions of the chaotic map with secret keys, which greatly improve the ability to withstand the known plaintext and chosen plaintext attacks. Simulation and performance analysis verify that this algorithm has acceptable compression, high security and low time complexity.

Wong et al. proposed a novel symmetric encryption scheme in which we can find the k-nearest neighbors from encrypted data and an encrypted query. Their scheme uses a pair of encryption functions that has an inner-product preserving property. Because of this property, the pair of encryption functions has been used in several encryption schemes involving ranked multi-keyword search as applications. On the other hand, Yao et al. pointed out that the pair of encryption functions is insecure when the attacker can get plaintext–ciphertext pairs. To prevent this attack, some countermeasures are given in the applications, e.g., randomizing plaintexts before encrypted. In this paper, we reanalyze the security of the inner-product preserving encryption functions. We first discuss the countermeasures against Yao et al.’s attack used in the applications. In particular, we show that one of them is ineffective. Next, we show that the first encryption function is breakable by the known plaintext attack by showing a concrete key-recovery procedure. Unlike Yao et al.’s attack, our attack does not use the second encryption function.

In the traditional image encryption systems, the permutation-diffusion operation is often conducted in two essentially separable or independent steps, which appears not only to be inefficient but also vulnerable in being attacked since each step can be targeted separately. In this paper, we propose a new plaintext-related cryptosystem in which the permutation-diffusion operation is performed in a simultaneous manner. More specifically, the simultaneous permutation-diffusion operation (PDSO) leads to the confusion and diffusion interacted each other, and thus generates better security level as well as higher efficiency of encryption process. The proposed encryption scheme only requires a single PDSO in the corresponding encryption process, in which the first encrypted pixel’s position in cipher image is randomly chosen and its value is determined by both pixels in the original image and the elements in key-streams obtained by three one-dimensional chaotic mappings, and the current encrypting pixel’s value is set to be associated with the previous encrypted pixel. Under our framework, the proposed encryption scheme is highly sensitive to minor differences in both secret key and plain image, resulting in resisting chosen/known plaintext attacks effectively. Simulation results show that the proposed scheme demonstrates excellent security capacity with high efficiency, comparing with existing approaches in literature.

Fully homomorphic encryption (FHE) has been regarded as the holy grail of cryptography and supports meaningful computations on encrypted data. Recently, Kumer et al. proposed a symmetric FHE scheme based on the Euler theorem. However, we illustrate in the paper that the secret key can be recovered from the homomorphic computation key and only a pair of known plaintext/ciphertext by computing the greatest common divisor with the Euclidean algorithm. Our observations are well supported by the numerical experiments on the suggested parameters. Furthermore, an improvement in the scheme is presented. We mimic Dijk et al.'s idea to illustrate that the improvement can be reduced to the approximate greatest common divisor (AGCD) problem. Several known attacks, including the proposal in this paper, are also examined.