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Plaintext-aware encryption is a simple concept: a public-key encryption scheme is plaintext aware if no polynomial-time algorithm can create a ciphertext without "knowing" the underlying message. However, the formal definitions of plaintext awareness are complex. This paper analyses these formal security definitions and presents the only known viable strategy for proving a scheme is PA2 plaintext aware. At the heart of this strategy is a new notion called PA1+ plaintext awareness. This security notion conceptually sits between PA1 and PA2 plaintext awareness (although it is formally distinct from either of these notions). We show exactly how this new security notion relates to the existing notions and how it can be used to prove PA2 plaintext awareness.

Bellare, Boldyreva, and O’Neill (CRYPTO ’07) initiated the study of deterministic public-key encryption as an alternative in scenarios where randomized encryption has inherent drawbacks. The resulting line of research has so far guaranteed security only for adversarially-chosen plaintext distributions that are independent of the public key used by the scheme. In most scenarios, however, it is typically not realistic to assume that adversaries do not take the public key into account when attacking a scheme.

Over the past two decades, chaos-based encryption appeared as an original application for nonlinear dynamics and deterministic chaos to encrypt and decrypt data. In this paper, an implementation of digital image encryption scheme based on the Lorenz chaotic system is proposed. While in the process of generating chaotic key stream, the hash value of the plain image is embedded in the proposed cryptosystem to dynamically alter the initial secret keys to increase the security level. The proposed digital image encryption algorithm is described in detail along with its security analysis and implementation. The experimental results show that the proposed digital image encryption algorithm is efficient and has high security features and is suitable for practical uses across insecure networks.

Recently, a feedback image encryption algorithm with compound chaotic stream cipher based on perturbation was proposed. This paper analyzes security of the algorithm and reports that there exist some security defects, i.e., encryption of a pixel is independent on the position scrambling and the encryption round is controlled by the users. Based on them, a chosen-ciphertext attack is proposed to obtain the equivalent version of the secret key of the algorithm with $$n\cdot \lceil \log _{256} MN +2 \rceil $$ chosen cipher-images, where $$M\times N$$ is the size of the corresponding plain-images and n is the round number of encryption.

Motivated by applications in large storage systems, we initiate the study of incremental deterministic public-key encryption. Deterministic public-key encryption, introduced by Bellare, Boldyreva, and O'Neill (CRYPTO '07), provides an alternative to randomized public-key encryption in various scenarios where the latter exhibits inherent drawbacks. A deterministic encryption algorithm, however, cannot satisfy any meaningful notion of security for low-entropy plaintexts distributions, but Bellare et al. demonstrated that a strong notion of security can in fact be realized for relatively high-entropy plaintext distributions. In order to achieve a meaningful level of security, a deterministic encryption algorithm should be typically used for encrypting rather long plaintexts for ensuring a sufficient amount of entropy. This requirement may be at odds with efficiency constraints, such as communication complexity and computation complexity in the presence of small updates. Thus, a highly desirable property of deterministic encryption algorithms is incrementality: Small changes in the plaintext translate into small changes in the corresponding ciphertext. We present a framework for modeling the incrementality of deterministic public-key encryption. Our framework extends the study of the incrementality of cryptography primitives initiated by Bellare, Goldreich and Goldwasser (CRYPTO '94). Within our framework, we propose two schemes, which we prove to enjoy an optimal tradeoff between their security and incrementality up to lower-order factors. Our first scheme is a generic method which can be based on any deterministic public-key encryption scheme, and, in particular, can be instantiated with any semantically secure (randomized) public-key encryption scheme in the random-oracle model. Our second scheme is based on the Decisional Diffie---Hellman assumption in the standard model. The approach underpinning our schemes is inspired by the fundamental "sample-then-extract" technique due to Nisan and Zuckerman (JCSS '96) and refined by Vadhan (J. Cryptology '04), and by the closely related notion of "locally computable extractors" due to Vadhan. Most notably, whereas Vadhan used such extractors to construct private-key encryption schemes in the bounded-storage model, we show that techniques along these lines can also be used to construct incremental public-key encryption schemes.

A symmetric key image cryptosystem based on the piecewise linear map is presented in this paper. In this cryptosystem, the encryption process and the decryption process are exactly same. They both include the same operations of plaintext-related scrambling once, diffusion twice and matrix rotating of 180 degrees four times. The length of secret key in the system is 64d where d is a positive integer. The proposed system can fight against the chosen/known plaintext attacks due to the using of plaintext-related scrambling. The simulate results and comparison analysis show that the proposed system has many merits such as high encryption/decryption speed, large key space, strong key sensitivity, strong plaintext sensitivity, strong cipher-text sensitivity, good statistical properties of cipher images, and large cipher-text information entropy. So the proposed system can be applied to actual communications.

We propose a novel color image encryption scheme based on DNA permutations. In the proposed scheme, the chaotic pseudo-random sequences for encryption depend on the plaintext image and secret keys. Besides, the proposed DNA permutation and addition/subtraction operations can break the bit planes of the plaintext image entirely. Therefore, the proposed scheme is sensitive to the plaintext image and can resist common attacks such as differential attack, brute-force attack, and statistical attack. Simulation results show the feasibility and effectiveness of the proposed scheme.

We give a new black-box transformation from any semantically secure encryption scheme into a non-malleable one which has a better rate than the best previous work of Coretti et al. (in: Kushilevitz and Malkin (eds) TCC 2016-A, Part I, Springer, Heidelberg, 2016). We achieve a better rate by departing from the "matrix encoding" methodology used by previous constructions, and working directly with a single codeword. We also use a Shamir secret-share packing technique to improve the rate of the underlying error-correcting code.

We show how to transform any semantically secure encryption scheme into a non-malleable one, with a black-box construction that achieves a quasi-linear blow-up in the size of the ciphertext. This improves upon the previous non-black-box construction of Pass, Shelat and Vaikuntanathan (Crypto '06). Our construction also extends readily to guarantee non-malleability under a bounded-CCA2 attack, thereby simultaneously improving on both results in the work of Cramer et al. (Asiacrypt '07). Our construction departs from the oft-used paradigm of re-encrypting the same message with different keys and then proving consistency of encryption. Instead, we encrypt an encoding of the message; the encoding is based on an error-correcting code with certain properties of reconstruction and secrecy from partial views, satisfied, e.g., by a Reed---Solomon code.

In order to construct efficient public-key encryption scheme that is secure against adaptive chosen-ciphertext attacks (CCA), an efficient signature scheme and an identity-based encryption (IBE) scheme from the learning with errors over rings are presented firstly in this paper, whose security are reducible to the hardness of the shortest vector problem in the worst case on ideal lattices. Secondly, a CCA-secure public key cryptosystem is constructed on the basis of the IBE and signature proposed above. The efficiency analysis indicates the proposed signature and encryption schemes are much more efficient than correlative cryptosystems. The security analysis shows that the IBE scheme is secure against chosen-plaintext attacks, and the public-key encryption scheme is CCA-secure in the random oracle model.

Shor proposed a quantum polynomial-time integer factorization algorithm to break the RSA public-key cryptosystem. In this paper, we propose a new quantum algorithm for breaking RSA by computing the order of the RSA ciphertext C. The new algorithm has the following properties: 1) recovering the RSA plaintext M from the ciphertext C without factoring n; 2) avoiding the even order of the element; 3) having higher success probability than Shor’s; 4) having the same complexity as Shor’s.

Attributed-based encryption (ABE) is a promising cryptographic access control mechanism with a rich expressiveness of ABE policies. Due to the high complexities of encryption and decryption, users are burdened with large computation cost. Fortunately, outsourcing technologies can be used to reduce the computation overhead for the ABE schemes. In the recent decade, the achievements of the outsourced ciphertext-policy ABE (CP-ABE) schemes are inspiring. But, the outsourcing encryption algorithms for CP-ABE schemes are not addressed properly since the encryption exponents are dynamic. In this paper, we present an efficient outsourced CP-ABE scheme with checkability, where the number of the exponential operations in the encryption can be reduced to a constant by introducing a blinding algorithm. Meanwhile, the ciphertext size is not increased. Furthermore, to guarantee the correctness of our scheme, we provide the verification mechanism based on a collision-resistance hash function, which allows the users to efficiently check the validity of messages and outsourced computation results. Besides, the proposed scheme is secure against replayable chosen ciphertext attacks based on Green’s outsourcing security model. Intensive experiments are carried out to illustrate the efficiency of the proposed scheme.

In this paper, we have developed a new ElGamal-like public key cryptosystem based on the matrices over a groupring. The underlying hard problem for this cryptosystem is the conjugacy search problem. That is, we have replaced the exponentiation of elements by conjugacy. This makes the key generation step more efficient. We also talk about different security aspects against known attacks. The proposed scheme is found to be secure against known plaintext attack when encryption uses a different random key for every new plaintext.

We give generic constructions of several fundamental cryptographic primitives based on a new encryption primitive that combines circular security for bit encryption with the so-called reproducibility property (Bellare et al. PKC 2003). At the heart of our constructions is a novel technique which gives a way of de-randomizing reproducible public-key bit-encryption schemes and also a way of reducing one-wayness conditions of a constructed trapdoor-function family (TDF) to circular security of the base scheme. The main primitives that we build from our encryption primitive include k-wise one-way TDFs (Rosen and Segev TCC 2009), CCA2-secure encryption and deterministic encryption. Our results demonstrate a new set of applications of circularly-secure encryption beyond fully-homomorphic encryption and symbolic soundness. Finally, we show the plausibility of our assumptions by showing that the DDH-based circularly-secure scheme of Boneh et al. (Crypto 2008) and the subgroup indistinguishability based scheme of Brakerski and Goldwasser (Crypto 2010) are both reproducible.

Recently, an image encryption algorithm based on hyper-chaotic system and dynamic S-box has been proposed by Liu et al. The main idea of the encryption algorithm is utilizing key-streams generated by hyper-chaotic system to permute and substitute plain-image pixels. In this paper, we analyze the potential security problems of the encryption algorithm in detail and propose a chosen-plaintext attack to break the encryption algorithm. The proposed chosen-plaintext attack indicates that the encryption scheme is insecure and not suitable for image secure communication. Based on the result of cryptanalysis, an improved algorithm is proposed to eliminate the potential security problem in Liu’s algorithm. Experimental results show that improved algorithm not only inherits the merits of the original scheme, but also has better cryptographic performances in statistical characteristics, plaintext sensitivity and key sensitivity.

In this paper, two efficient cryptosystem schemes in the form of permutation–substitution based on chaotic systems are proposed. Firstly, a simple and efficient S-box method is introduced in order to use this S-box designed scheme in secure color image encryption technique. The major advantage of the proposed strategy is the dynamic aspect of keys used by chaotic map to generate strong S-boxes. Secondly, an efficient color encryption scheme based on chaotic maps and S-boxes in the form of permutation–substitution network is developed. Experimental results show the effectiveness of the proposed schemes. The suggested cryptosystems have superior performance and great potential for prominent prevalence in cryptographic applications compared to previous schemes.

Image encryption has been an attractive research field in recent years. The chaos-based cryptographic algorithms have suggested some new and efficient ways to develop secure image encryption techniques. This paper proposes a novel image encryption scheme, which is based on the chaotic tent map. Image encryption systems based on such map show some better performances. Firstly, the chaotic tent map is modified to generate chaotic key stream that is more suitable for image encryption. Secondly, the chaos-based key stream is generated by a 1-D chaotic tent map, which has a better performance in terms of randomness properties and security level. The performance and security analysis of the proposed image encryption scheme is performed using well-known ways. The results of the fail-safe analysis are inspiring, and it can be concluded that the proposed scheme is efficient and secure.

A bit-oriented quantum public-key encryption scheme is presented. We use Boolean functions as private-key and randomly changed pairs of quantum state and classical string as public-keys. Following the concept of quantum perfect encryption, we prepare the public-key with Hadamard transformation and Pauli transformation. The quantum part of public-keys is various with different classical strings. In contrast to the typical classical public-key scheme, one private-key in our scheme corresponds to an exponential number of public-keys. We investigate attack to the private-key and prove that the public-key is a totally mixed state. So the adversary cannot acquire any information about private-key from measurement of the public-key. Then, the attack to encryption is analyzed. Since the trace distance between two different ciphertexts is zero, the adversary cannot distinguish between the two ciphertext states and also obtains nothing about plaintext and private-key. Thus, we have the conclusion that the proposed scheme is information-theoretically secure under an attack of the private-key and encryption.

In recent years, a wide variety of cryptographic algorithms based on chaos have been put forward and most of them have been proved to be successful by adopting the traditional permutation-diffusion architecture. However, one drawback these methods mostly hold is that they have little connection with the plaintext or, properly speaking, the relationship between them is rather less. The drawback makes the encryption algorithms vulnerable to the known-plaintext and chosen-plaintext attack. In addition, the secret keys are stationary at most times, and they can't be selected dynamically by the corresponding plain image pixels. In order to overcome these disadvantages mentioned above, we introduce a new chaos-based image encryption algorithm with dynamic key selection mechanisms in this paper, and present a dynamic keystream sequence group selection mechanism (DKSGSM) and a dynamic keystream selection mechanism (DKSM). They strongly enhance the relationship between the plaintext and the encryption scheme. In particular, the DKSGSM and DKSM expand the selection range of the keys and allow us to select the keys dynamically by the corresponding plaintext pixels. What's more, by adopting the bidirectional encryption, we can spread the influence to the whole image once a tiny change in plain image and this can greatly increase the security level of our encryption method. Simulation results and numerical analyses indicate that our encryption scheme is safe and efficient.

Goldwasser and Micali (J Comput Syst Sci 28(2):270---299, 1984) highlighted the importance of randomizing the plaintext for public-key encryption and introduced the notion of semantic security. They also realized a cryptosystem meeting this security notion under the standard complexity assumption of deciding quadratic residuosity modulo a composite number. The Goldwasser---Micali cryptosystem is simple and elegant but is quite wasteful in bandwidth when encrypting large messages. A number of works followed to address this issue and proposed various modifications. This paper revisits the original Goldwasser---Micali cryptosystem using $$2^k$$2k-th power residue symbols. The so-obtained cryptosystems appear as a very natural generalization for $$k \ge 2$$kź2 (the case $$k=1$$k=1 corresponds exactly to the Goldwasser---Micali cryptosystem). Advantageously, they are efficient in both bandwidth and speed; in particular, they allow for fast decryption. Further, the cryptosystems described in this paper inherit the useful features of the original cryptosystem (like its homomorphic property) and are shown to be secure under a similar complexity assumption. As a prominent application, this paper describes an efficient lossy trapdoor function-based thereon.

Paterson and Quaglia (SCN 2010) proposed the concept of time-specific encryption (TSE) and its efficient constructions. TSE is a type of public-key encryption with an additional functionality where an encryptor can specify a suitable time interval, meaning that the ciphertexts may only be decrypted within this time interval. In this work, we propose a new methodology for designing efficient TSE schemes by using forward-secure encryption (FSE), and based on this methodology, we present a specific TSE scheme using Boneh---Boyen---Goh FSE, and a generic construction from any FSE. Our proposed TSE schemes are practical in all aspects with regard to computational costs and data sizes. The sizes of the ciphertext and the public parameter in our schemes are significantly smaller than those in previous schemes in an asymptotic sense.

Due to the interesting nonlinear dynamic properties of chaotic maps, recently chaos-based encryption algorithms have gained much attention in cryptographic communities. However, many encryption schemes do not fulfil the minimum key space requirement, which is an essential concern in many secure data applications. In this paper, an efficient chaos-based image encryption scheme with higher key space is presented. Even with a single round of encryption, a significantly larger key space can be achieved. The proposed scheme removes correlation among image pixels via random chaotic sequences, simply by XOR and addition operations. In order to resist against numerous attacks, we apply the affine transformation to get the final ciphertext image. The security of the proposed scheme is proved through histogram, contrast, PSNR, entropy, correlation, key space, key sensitivity and differential attack analysis. Many significant properties of chaotic maps, sensitivity to initial condition and control parameters, structure and attack complexity, make the anticipated scheme very reliable, practical and robust in various secure communication applications.

In this paper, we propose a novel image encryption algorithm based on a hybrid model of deoxyribonucleic acid (DNA) masking, a Secure Hash Algorithm SHA-2 and the Lorenz system. Our study uses DNA sequences and operations and the chaotic Lorenz system to strengthen the cryptosystem. The significant advantages of this approach are improving the information entropy which is the most important feature of randomness, resisting against various typical attacks and getting good experimental results. The theoretical analysis and experimental results show that the algorithm improves the encoding efficiency, enhances the security of the ciphertext and has a large key space and a high key sensitivity, and it is able to resist against the statistical and exhaustive attacks.

The traffic of digital images has been quickly increased in the network. Security of image processing became important for many sectors, namely for medical applications. Currently, the transmission of medical images is a daily routine. The large volume of data exchange has motivated the development of new methods to reduce the cost. Partial encryption is an approach to reduce the computational resources for huge volumes of multimedia. This paper introduces a new and secure approach, called graph coloring problem cryptography, to encrypt partially the medical images using the graph coloring problem (GCP). Before encrypting the medical images using advanced encryption standard algorithm, we use a GCP algorithm to localize and select some optimal positions of the pixels in the original images. Thus, the key of the cryptographic method is hard to be detected and extracted by the hackers. We get an acceptable percentage of the encrypted data for better security with a lower cost compared with the total image encryption.

Public-key encryption can be used to protect the sensitive data in cloud system with intelligent mobile agents facilitating better services. However, many public-key encryption schemes do not resist the side-channel attacks which can be applied to the encryption instances implemented on a chip or cloud to obtain partial information leakage about the secret states, as the traditional security model of public-key encryption does not capture this kind of attacks. Also, the adversary can inject fault to tamper with the secret key and observe the output of the public-key encryption scheme under this modified key which is called "related-key attacks". Inspired by these, the models of key-leakage attacks and related-key attacks are formalized, respectively. In this paper, we present a method to construct public-key encryption schemes against both weak key-leakage attacks and linear related-key attacks from extractable hash proof systems (EHPS or XHPS). Specifically, we first transform ABOEHPS to weak leakage-resilient ABOEHPS and add Key Homomorphism and Fingerprinting properties to it. Then, based on this new ABOEHPS, we construct weak leakage-resilient adaptive trapdoor relation with these two properties and public-key encryption schemes against both weak key-leakage attacks and linear related-key attacks can be constructed from it. Moreover, we propose a public-key encryption scheme against both adaptive key-leakage attacks and linear related-key attacks.

Nonlinear delay differential system (NDDS) is a family of hyperchaotic systems, which has attracted much attention in the last years, especially in optics. The NDDS is often modeled by a time delay that occurs between the signals at the input and the output, and a nonlinearity introduced by a function $$F$$ . This paper introduces the Ikeda system that is considered system of infinite dimension and proposed an image encryption scheme by dynamic block. The encryption algorithm divides the image on dynamic blocks depending on the previous block cipher. The algorithm diffuses the plain image with bitwise XOR between each block and sequence generated by Ikeda system after quantification. Statistical analysis of the proposed encryption scheme demonstrates that this cryptosystem is secure enough to resist the brute-force attack, entropy attack, differential attack, chosen-plaintext attack, known-plaintext attack and statistical attack. In addition, the cryptosystem has high sensitivity of key and large space key.

Wang and Guo (Nonlinear Dyn 76(4):1943–1950, 2014) proposed a new image alternate encryption algorithm based on chaotic map. The image alternate encryption can be conceptually treated as a block cipher where a round function which provides both confusion and diffusion is applied on a plain image iteratively. After performing the round function for \(T\) iterations, the processed image is denoted as the encrypted image. We analyse the security of Wang and Guo image encryption scheme, especially from cryptographic point of view, in line with the designers’ approach in their security analyses. Negatively, we show that the image encryption scheme is vulnerable to an impossible differential attack (a type of chosen plaintext attack) and a divide-and-conquer attack when a large all black image is encrypted. This paper serves as another important security result showing that any future design of image encryption schemes based on chaotic map should be evaluated through systematic cryptanalytic approaches which include impossible differential attack. To the best of our knowledge, this is the first impossible differential attack applied on an image encryption algorithm.

The principle of compressed sensing (CS) can be applied in a cryptosystem by providing the notion of security. In this paper, we study the computational security of a CS-based cryptosystem that encrypts a plaintext with a partial unitary sensing matrix embedding a secret keystream. The keystream is obtained by a keystream generator of stream ciphers, where the initial seed becomes the secret key of the CS-based cryptosystem. For security analysis, the total variation distance, bounded by the relative entropy and the Hellinger distance, is examined as a security measure for the indistinguishability. By developing upper bounds on the distance measures, we show that the CS-based cryptosystem can be computationally secure in terms of the indistinguishability, as long as the keystream length for each encryption is sufficiently large with low compression and sparsity ratios. In addition, we consider a potential chosen plaintext attack (CPA) from an adversary, which attempts to recover the key of the CS-based cryptosystem. Associated with the key recovery attack, we show that the computational security of our CS-based cryptosystem is brought by the mathematical intractability of a constrained integer least-squares (ILS) problem. For a sub-optimal, but feasible key recovery attack, we consider a successive approximate maximum-likelihood detection (SAMD) and investigate the performance by developing an upper bound on the success probability. Through theoretical and numerical analyses, we demonstrate that our CS-based cryptosystem can be secure against the key recovery attack through the SAMD.

Recently, a block cryptosystem based on iterating a chaotic map is analyzed and improved. But still four security flaws in this improved cryptosystem have been identified with careful analysis. First, the first block of ciphertext is identical to the corresponding plaintext in special circumstances. Second, an important parameter can be obtained with a chosen ciphertext attack. Third, with this parameter, a known block of ciphertext, and the corresponding block of plaintext, a block of plaintext can be recovered by chosen ciphertext attack. Forth, the relationship between every two blocks of the keystream can be determined, leading to the recovery of the entire keystream if a single block of the keystream can be obtained. Those four security flaws render the cryptosystem insecure for general use.

This study deals with the dynamic property of threshold cryptosystem. A dynamic threshold cryptosystem allows the sender to choose the authorized decryption group and the threshold value for each message dynamically. We first introduce an identity based dynamic threshold cryptosystem, and then use the Canetti-Halevi-Katz (CHK) transformation to transform it into a fully secure system in the traditional public key setting. Finally, the elegant dual system encryption technique is applied to constructing a fully secure dynamic threshold cryptosystem with adaptive security.

Recently, a novel image encryption algorithm based on DNA operation and hyper-chaotic system has been proposed by Zhang et al. The encryption algorithm first shuffles the image pixels using Chen chaotic system. After shuffling process, the proposed encryption algorithm changes the gray levels of the image pixels using DNA operation. In this study, we give out complete break for the proposed cryptosystem using a chosen plaintext attack. Both mathematical proofs and experimental results are presented to support the proposed attacks. Main motivation behind this study was to analyze whether proposed image encryption algorithm is suitable for secure communication or not. Based on the results of our analysis, we also discussed the potential improvements for the algorithm and proposed a modified new encryption algorithm accordingly. Essential elements of designing secure image encryption algorithms and potential application areas are also stated.

The security analysis of physical encryption protocol based on coherent pulse position modulation (CPPM) originated by Yuen is one of the most interesting topics in the study of cryptosystem with a security level beyond the Shannon limit. Although the implementation of CPPM scheme has certain difficulty, several methods have been proposed recently. This paper deals with the CPPM encryption in terms of symplectic transformation, which includes a phase mask encryption as a special example, and formulates a unified security analysis for such encryption schemes. Specifically, we give a lower bound of Eve's symbol error probability using reliability function theory to ensure that our proposed system exceeds the Shannon limit. Then we assume the secret key is given to Eve after her heterodyne measurement. Since this assumption means that Eve has a great advantage in the sense of the conventional cryptography, the lower bound of her error indeed ensures the security level beyond the Shannon limit. In addition, we show some numerical examples of the security performance.

In this paper, we present an image encryption scheme that has the capability to tolerate noisy effects of a wireless channel. This means if the encrypted image data is corrupted by channel noise up to a certain level, correct decryption is possible with some distortion. The proposed image encryption scheme relies on some very interesting properties of orthogonal matrices containing columns that form a set of orthonormal basis vectors. Besides being tolerant to noisy channels, the proposed scheme also provides good security against well-known cryptographic attacks as demonstrated in this paper by a number of experimental results and security analysis.

Recently, a novel bilateral-diffusion image encryption algorithm based on dynamical compound chaos function and LFSR was proposed. The core idea of the algorithm is to introduce the bilateral-diffusion approach. The present paper focuses mainly on security evaluation of this approach. As it is well known, the security of a cryptosystem must depend only on the secrecy of the key rather than the secrecy of the algorithm according to Kerckoff’s principle. The security of the original algorithm is determined by two initial keys. Since the keys are fixed, the chaotic keystream keeps unchanged for different images. Thus, our purpose is to reveal the keystream. The cryptanalytic results show that the whole keystream can be broken by using two images including a chosen image and a known image, with a combination of chosen-plaintext attack and known-plaintext attack.

Recently a new image encryption method based on DNA encoding and chaotic systems has been proposed. In this paper, several weaknesses of this cryptosystem are pointed out. Equivalent mathematical model of the cryptosystem is designed and algebraic analysis is given. Moreover reduction of the key space has been reached by finding equivalent keys. A recovering scheme is finally given with a lower complexity than the actual decryption scheme.

A chaos-based cryptosystem has exhibited some unconventionally excellent properties. At the same time, it is of vital significance for its advancement to give a mathematically rigorous cryptanalysis. In this study, we analyze the security of an image encryption algorithm, whose main idea is to use the sum of image data for encryption. By applying known plaintext and chosen plaintext attacks, we show that all the secret keys can be revealed.

The notion of certificateless public-key encryption (CL-PKE) was introduced by Al-Riyami and Paterson in 2003 that avoids the drawbacks of both traditional PKI-based public-key encryption (i.e., establishing public-key infrastructure) and identity-based encryption (i.e., key escrow). So CL-PKE like identity-based encryption is certificate-free, and unlike identity-based encryption is key escrow-free. In this paper, we introduce simple and efficient CCA-secure CL-PKE based on (hierarchical) identity-based encryption. Our construction has both theoretical and practical interests. First, our generic transformation gives a new way of constructing CCA-secure CL-PKE. Second, instantiating our transformation using lattice-based primitives results in a more efficient CCA-secure CL-PKE than its counterpart introduced by Dent in 2008.

Wireless sensor network (WSN) needs efficient and secure and simple algorithms to be implemented in order to assure confidential communications between nodes and base station. The most suitable kind of algorithm seems to be the partial encryption ciphers. MPEG video encryption can be done by selecting the most significant parts of this sequence which are the group of pictures known as the I-frames. In this letter, we study the security of a partial video encryption method by Yang and Sun (Prog Nat Sci 18:1299–1304, 2008) that can be used in video nodes in a WSN. Based on the given analysis, it is demonstrated that the cryptosystem under study has serious weaknesses in the shuffling and the mixing processes which makes it vulnerable to chosen plaintext attack. Through the studied cipher, we question whether practitioners should design their own new ciphers for their specific applications or should they use well-known ciphers and fit them to their applications.

As the basis for secure public-key encryption under various cases, the learning with errors (LWE) problem has proved to be versatile for encryption schemes. Unfortunately, it tends not to be efficient enough for practical applications. For improving the efficiency issues and quickening the practical applications of the lattice-based public-key cryptosystems, an efficient homomorphic encryption scheme is presented in this paper, which is based on the learning with errors over rings (R-LWE) assumption, and its security is reducible to the hardness of the shortest vector problem in the worst case on ideal lattices. Furthermore, the scheme possesses homomorphism feature that encryption operations are consistent with message operations. The security analysis shows that the proposed encryption scheme is secure against chosen-plaintext attacks in the standard model. At the same time, the efficiency analysis and simulation results indicate that the scheme is much more efficient than previous lattice-based cryptosystems.

In this paper, we propose to cryptanalyse an encryption algorithm which combines a DNA addition and a chaotic map to encrypt a gray scale image. Our contribution consists on, at first, demonstrating that the algorithm, as it is described, is non-invertible, which means that the receiver cannot decrypt the ciphered image even if he posses the secret key. Then, a chosen plaintext attack on the invertible encryption block is described, where, the attacker can illegally decrypt the ciphered image by a temporary access to the encryption machinery.

For an encryption scheme to be applied in practical applications, it should withstand various leakage attacks. In this paper, we present a new leakage-resilient public key encryption scheme whose security is based on the classical DDH (decisional Diffie-Hellman) assumption. In the computational cost, our proposed scheme is more efficient than the original Cramer-Shoup leakage-resilient public key encryption scheme. At the same time, our new scheme also enjoys a shorter (public and secret) key length, and a higher relative key leakage ratio. We formally prove our new proposal is semantically secure against adaptive posteriori chosen ciphertext key-leakage attacks assuming the hardness of the DDH problem without random models.

Recently, a parallel sub-image encryption method with high-dimensional chaos has been proposed. But there is a fatal flaw in the cryptosystem that the generated keystream remains unchanged when encrypting every image. Based on this point, we could recover the plaintext by applying chosen plaintext attack. Therefore the proposed cryptosystem is not supposed to be used in image transmission system. Experimental results show the feasibility of our attack.

Deterministic public-key encryption, introduced by Bellare, Boldyreva, and O'Neill (CRYPTO '07), provides an alternative to randomized public-key encryption in various scenarios where the latter exhibits inherent drawbacks. A deterministic encryption algorithm, however, cannot satisfy any meaningful notion of security when the plaintext is distributed over a small set. Bellare et al. addressed this difficulty by requiring semantic security to hold only when the plaintext has high min-entropy from the adversary's point of view. In many applications, however, an adversary may obtain auxiliary information that is related to the plaintext. Specifically, when deterministic encryption is used as a building block of a larger system, it is rather likely that plaintexts do not have high min-entropy from the adversary's point of view. In such cases, the framework of Bellare et al. might fall short from providing robust security guarantees. We formalize a framework for studying the security of deterministic public-key encryption schemes with respect to auxiliary inputs. Given the trivial requirement that the plaintext should not be efficiently recoverable from the auxiliary input, we focus on hard-to-invert auxiliary inputs. Within this framework, we propose two schemes: the first is based on the d-linear assumption for any d?1 (including, in particular, the decisional Diffie---Hellman assumption), and the second is based on a rather general class of subgroup indistinguishability assumptions (including, in particular, the quadratic residuosity assumption and Paillier's composite residuosity assumption). Our schemes are secure with respect to any auxiliary input that is subexponentially hard to invert (assuming the standard hardness of the underlying computational assumptions). In addition, our first scheme is secure even in the multi-user setting where related plaintexts may be encrypted under multiple public keys. Constructing a scheme that is secure in the multi-user setting (even without considering auxiliary inputs) was identified by Bellare et al. as an important open problem.

We present a new primitive of randomized message-locked encryption (MLE) in this paper and define a new security model for it. The new primitive, named message-locked encryption3 (hereafter referred as MLE3), is actually a variant of randomized message-locked encryption (Bellare et al. Eurocrypt13). In order to prevent trivial attacks, our primitive admits a semi-trusted server, which is allowed to hold a secret key of public key encryption (PKE), to verify the correctness of a tag. The new security notion, called privacy chosen-distribution attacks3 (PRV-CDA3), requires that a ciphertext generated by encrypting an unpredictable message and another ciphertext (possible invalid) chosen randomly from a ciphertext space are indistinguishable. Compared with the priori proposed security notion, privacy chosen-distribution attacks (PRV-CDA) (Bellare et al. Eurocrypt13), which requires that two ciphertexts generated by encrypting two unpredictable messages are indistinguishable, the security notion we propose is much stronger. Based on the new primitive, under the blackbox reductions, we put forward a novel construction which achieves both privacy chosen-distribution attacks3 (PRV-CDA3) and strong tag consistency (STC) securities in the standard model via universal computational extractors (UCEs) (Bellare et al. Crypto13). In addition, our scheme also provides the validity-testing for ciphertext.

Chaotic cryptography has been applied to image encryption; however, only the traditional low-dimensional chaotic systems has been widely analyzed or deciphered, which does not show satisfied security and efficiency. To solve this problem, a new algorithm based on cross-chaos map has been created in this article. The image pixels are scrambled under control of high-dimensional chaotic sequence, which is generated by cross chaotic map. The image pixels are substituted by ciphertext feedback algorithm. It can relate encryption required parameters with plaintext and can make a plaintext byte affect more ciphertext bytes. Proved by theoretical analysis and experimental results, the algorithm has higher complex degree and has passed SP800-22 pseudo-random number standard tests, and it has high encryption speed, high security, etc. It can be widely applied in the field of image encryption.

This paper proposes breaks for the total shuffling scheme adopted in the skew tent-map-based image cryptosystem. By applying chosen plaintext combined with chosen ciphertext attack, we demonstrate that a hacker can determine the permutation vector and the whole random code sequence used respectively in permutation and diffusion procedure, which can be exploited to reveal the plain image. Then we proposed an improved algorithm based on the skew tent map. The theoretical analysis and experimental results indicate that the improved algorithm can overcome these flaws and has better cryptographic performances in resisting against chosen plaintext and chosen ciphertext attacks, randomness, and sensitivity.

Recently, a colour image encryption algorithm based on chaos was proposed by cascading two position permutation operations and one substitution operation, which are all determined by some pseudo-random number sequences generated by iterating the logistic map. This paper evaluates the security level of this encryption algorithm and finds that the position permutation-only part and the substitution part can be separately broken with only ⌈(log2(3MN))/8⌉ and 2 chosen plain-images, respectively, where MN is the size of the plain-image. The effectiveness of the proposed chosen-plaintext attack is supported by concise theoretical analyses, and is verified by experimental results.

Real-time video streams require an efficient encryption method to ensure their confidentiality. One of the major challenges in designing a video encryption algorithm is to encrypt the vast amount of video data in real-time to satisfy the stringent time requirements. Video encryption algorithms can be classified according to their association with video compression into joint compression and encryption algorithms and compression-independent encryption algorithms. The latter have a clear advantage over the former regarding the incorporation into existing multimedia systems due to their independence of the video compression. In this paper we present the compression-independent video encryption algorithm Puzzle, which was inspired by the children game jigsaw puzzle. It comprises two simple encryption operations with low computational complexity: puzzling and obscuring. The scheme thereby dramatically reduces the encryption overhead compared to conventional encryption algorithms, such as AES, especially for high resolution video. Further outstanding features of Puzzle are a good trade-off between security demands and encryption efficiency, no impairment on video compression efficiency, and an easy integration into existing multimedia systems. This makes Puzzle particularly well-suited for these security-sensitive multimedia applications, such as videoconferencing, where maximal security and minimal encryption overhead are desired simultaneously.

The main contributions of this paper are twofold. On the one hand, the twin Diffie---Hellman (twin DH) problem proposed by Cash et al. is extended to the n-Diffie---Hellman (n-DH) problem for an arbitrary integer n, and this new problem is shown to be at least as hard as the ordinary DH problem. Like the twin DH problem, the n-DH problem remains hard even in the presence of a decision oracle that recognizes solution to the problem. On the other hand, observe that the double-size key in the Cash et al. twin DH-based encryption scheme can be replaced by two separated keys each for one entity that results in a 2-party encryption scheme which holds the same security feature as the original scheme but removes the key redundancy. This idea is further extended to an n-party case, which is also known as n-out-of-n encryption. As examples, a variant of ElGamal encryption and a variant of Boneh---Franklin IBE have been presented; both of them have proved to be chosen ciphertext attack secure under the computational DH assumption and the computational bilinear Diffie---Hellman assumption, respectively, in the random oracle model. The two schemes are efficient, due partially to the size of their ciphertext, which is independent to the value n.

An encryption scheme is non-malleable if giving an encryption of a message to an adversary does not increase its chances of producing an encryption of a related message (under a given public key). Fischlin introduced a stronger notion, known as complete non-malleability, which requires attackers to have negligible advantage, even if they are allowed to transform the public key under which the related message is encrypted. Ventre and Visconti later proposed a comparison-based definition of this security notion, which is more in line with the well-studied definitions proposed by Bellare et al. The authors also provide additional feasibility results by proposing two constructions of completely non-malleable schemes, one in the common reference string model using non-interactive zero-knowledge proofs, and another using interactive encryption schemes. Therefore, the only previously known completely non-malleable (and non-interactive) scheme in the standard model, is quite inefficient as it relies on generic NIZK approach. They left the existence of efficient schemes in the common reference string model as an open problem. Recently, two efficient public-key encryption schemes have been proposed by Libert and Yung, and Barbosa and Farshim, both of them are based on pairing identity-based encryption. At ACISP 2011, Sepahi et al. proposed a method to achieve completely non-malleable encryption in the public-key setting using lattices but there is no security proof for the proposed scheme. In this paper we review the mentioned scheme and provide its security proof in the standard model. Our study shows that Sepahi's scheme will remain secure even for post-quantum world since there are currently no known quantum algorithms for solving lattice problems that perform significantly better than the best known classical (i.e., non-quantum) algorithms.