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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.

In this paper, a color image encryption algorithm based on Fisher-Yates scrambling and DNA subsequence operation (elongation operation, truncation operation, deletion operation, insertion arithmetic) is proposed. Firstly, the three-dimensional color image is transformed into two-dimensional gray image, and the chaotic sequence generated by Chen system and Fisher-Yates scrambling method is used to scramble the plaintext images of R, G and B channels. Secondly, the three channel images of the scrambled plaintext image are transformed into three DNA sequence matrixes by using the DNA coding rules, and then the three DNA sequence matrixes are manipulated by using DNA subsequence operation and DNA addition, subtraction and XOR operation to destroy the scrambled plaintext information. Finally, the color encrypted image is obtained by using the DNA decoding rule. Experimental results and security analysis demonstrate that our encryption algorithm has good performance and may resist against various typical attacks.

The double random phase encoding techniques have received considerable attention from researchers in recent years because of their advantages of parallel and high-speed processing capability. Meanwhile, the security of the cryptosystem is also one of the major concerns. We experimentally showed the ciphertext redundancy vulnerability of the coherent double random phase encryption (DRPE) system. Based on the statistical ergodicity of speckles and the consistency of the energy spectral density (ESD), we have proved that the method can retrieve the most plaintext information from partial ciphertext alone. We performed the simulation and experimental results to verify whether the algorithm is effective. The ciphertext redundancy of the DRPE system is analyzed from the results of the ciphertext occlusion test. There is a risk of plaintext leakage in this scheme, as long as the average ESD can be estimated from the sub-images. The results will further our understanding of the limitation of current optical security techniques. The DRPE system has potential redundancy risk. This vulnerability allows a cryptanalyst to estimate the plaintext information with only a half or less ciphertext.

The existing image encryption schemes are not suitable for the secure transmission of large amounts of data in range-gated laser imaging under high noise background. Aiming at this problem, a range-gated laser imaging image compression and encryption method based on bidirectional diffusion is proposed. The image data collected from the range-gated laser imaging source is sparsely represented by the discrete wavelet transform. Arnold chaotic system is used to scramble the sparse matrix, and then the measurement matrix is constructed by the quantum cellular neural network (QCNN) to compress the image. In addition, the random sequence generated by QCNN hyperchaotic system is used to carry out “bidirectional diffusion” operation on the compression result, so as to realize the security encryption of image data. The comparative analysis of the security encryption performance of different compression ratios shows that the histogram sample standard of the encrypted image can reach about 10, and the information entropy value is more than 7.99, which indicates that the encryption scheme effectively hides the plaintext information of the original image. When the encrypted image is attacked by different degrees of noise, this method can still reconstruct the image through the effective decryption process. The experimental results show that this method realizes the secure compression and encryption of gated-laser imaging image data, and effectively ensures the security of data while reducing the amount of channel transmission data.

In order to solve the problem of plaintext data leakage, and to improve the diversity and security of biometric template, this paper proposes a high security BioHashing encrypted speech retrieval algorithm based on feature fusion, and introduces K-means-KNN fusion algorithm to classify. Firstly, the features of speech are extracted through FFT and IFFT. Secondly, the fused features are classified and a single mapping secret key is assigned to each class. The improved Marotto chaos measurement matrix is generated by the secret key, and the BioHashing sequences are generated by iterating the measurement matrix with the feature data. Then, the speech clips are classified and a single mapping secret key is assigned to each class. The SPM(sine map and piece wise linear chaotic map) chaotic sequence is generated by the secret key and the speech clips are encrypted by the sequence. Finally, hash indexes and encrypted speech clips are uploaded to the cloud, the normalized Hamming distance algorithm is used for matching retrieval on the user terminal. Experimental results show that the algorithm not only effectively prevents plaintext data leakage, but also achieves 100% retrieval accuracy for the original speech clips. Moreover, there are 18 classes of biometric templates, which have good security and key revocability.

According to the research works of the references on chaotic cryptanalysis, many recent chaotic image encryption algorithms cannot resist chosen-plaintext attacks. Although some chaotic image encryption algorithms introduce plain-image information, they still violate some design requirements of modern cryptosystems. The traditional image encryption algorithm has the disadvantages of low security and time-consuming. Therefore, after analyzing many literatures related to chaotic image encryption and aiming to improve the security of ciphertext and effectively resist plaintext attack, we propose a hybrid chaotic system-oriented artificial fish swarm neural network method for image encryption. Firstly, based on the nonlinear combination theory, the Logistic, Tent and Sine mappings are used to design the hybrid complex chaotic system. According to the pixel value of plaintext, it generates the initial value to output the chaotic sequence. Taking a chaotic sequence as the input layer, the artificial neural network is introduced to train and learn the chaotic sequence. It eliminates the chaotic periodicity and outputs the neural network sequence. The artificial fish swarm algorithm is used to optimize the initial weight and threshold of the Elman neural network. The set obfuscation method is defined to scramble the plaintext. A quantization method is constructed to quantify the neural network sequence and obtain the key flow. The mixed images are classified, the key flow is combined, the pixel value is changed and the ciphertext is output by designing the piecewise diffusion technology. Experimental results show that compared with the current state-of-the-art image encryption methods, the proposed algorithm has higher security and resist plaintext attack ability.

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.

In this paper, an image cipher is presented based on DNA sequence operations, image filtering and memrisitve chaotic system. Firstly, plain image is preprocessed by a self-updating transformation based on dynamic image filtering (STDIF), which may solve the problem that conventional filtering is invalid for special image such as all-zeros. Subsequently, the resulting image is converted into the DNA sequences by the dynamic DNA encoding rules, and the rules are produced by plain image information and chaotic system. Next, the DNA matrix is permutated by a double random 3D matrix scrambling (DR3DMS), thus every element may arbitrarily move to other position. Thereafter, the permutated matrix is diffused by a plane diffusion of 3D DNA matrix controlled by plain image information (PD3DPI) to resist statistical attacks. Finally, the obtained DNA matrix is transformed into cipher image via DNA decoding rules. Additionally, SHA 256 hash function value of plain image is applied to choose keystreams from the obtained chaotic sequences, which not only solves the problem of repeatedly generating chaotic sequences when encrypting different images, but also results into higher difficulty for hackers to decipher the method by use of plaintext attack. Experimental results and security analyses demonstrate its security and effectiveness.

Attribute-based encryption (ABE) provides a fine-grained access control mode for multiuser network environments. The popularity of 5th generation (5G) mobile network applications has greatly increased the data transmission rate, but mobile terminal devices with limited resources in the network have difficulty with the high computational overhead of ABE in wireless communication. In response to this problem, this paper proposes a hybrid encryption online/offline ciphertext policy attribute-based encryption (CP-ABE) scheme for 5G. In the scheme, the data owner uses symmetric encryption technology to perform data encapsulation on plaintext and outsources the encapsulated plaintext to the cloud user assistant (CUA) for offline calculation. Key encapsulation is performed on a symmetric key to form the final ciphertext, and it is uploaded to the cloud server. After the data user obtains the ciphertext, it is handed over to the CUA for offline decryption calculation. If the access structure is satisfied, the encapsulated ciphertext can be obtained, and then the symmetric key is used to decrypt the ciphertext. In the scheme, the correctness of the symmetric key can be verified to prevent malicious tampering in the process of transmission. It is indicated that the scheme is secure after being tested with the decisional q-Parallel Bilinear Diffie-Hellman Exponent (BDHE). Numerical analysis shows that the scheme has decreased computational overhead and can achieve fine-grained access control of user decryption rights.

To overcome the worse statistical proprieties of digital chaotic maps, this paper proposes a modified version of the Henon chaotic map using a cosine function. What is new in this proposal is that the cosine function replaces only the nonlinear part of the chaotic map which increases the chaotic proprieties compared to other proposals. On the other hand, adding a constant with a high value ( $$F > 10^4$$ ) to the new control parameter eliminates the small zones of stability that cannot be observed easily. The improved Henon map has been evaluated in terms of randomness quality using a set of mathematical tools, in which good results have been obtained. The improved map is used to design a cryptosystem; we have proposed an efficient method for the aim of ensuring the diffusion property by feeding back the encrypted message to the modified map. So, a very small change on the plaintext leads to a different chaotic state. The proposed encryption scheme has been evaluated in terms of security, in which some known cryptographic attacks have been performed on it. The results showed that the proposed encryption scheme meets the nowadays security requirements. The proposed encryption scheme is evaluated in real-time using low-cost ARM (Cortex-M3 32-bit RISC core) under two different scenarios, emitter, and receiver, which are connected wirelessly. A comparison with some existing solutions showed that our proposal provides a good ratio between randomness, implementation cost, and performance.

To protect the privacy of medical images, as well as the patient personal information associated with it, this paper proposes a reversible data hiding scheme for encrypted medical images; whose reversibility is completely separable by allowing additional data extraction and restoration of the region of interest both from the plaintext and the cipher domain of medical images. To this purpose, the pixels in the image are reordered according to the region of interest selected by the content owner and encrypted with a block cipher in counter mode; to subsequently embed additional data into the encrypted image, such as the patient’s personal information and clinical diagnosis, via less significant bit substitution. Finally, according to the proper key, a legitimate receiver can perform the following tasks: a) Obtain a high visual quality approximate image with respect to the original version by directly decrypting the cryptogram with the encryption key, b) With the data hiding key, the embedded data can be extracted free of any error, either from the encrypted image or its approximate version respectively, and c) In case of having both keys, the embedded data can be extracted and the recovered image with the region of interest fully restored can be obtained without loss of information. The proposed method is suitable for applications where the information security and the management of medical images need to be ensured in terms of reliability, integrity, and confidentiality. Comparison performance with the state of the art is performed, in terms of imperceptibility, capacity and steganalysis.

To enhance the security of single-chaotic systems, we propose a novel image encryption cryptosystem based on true random numbers and chaotic systems. First, we select any one of several chaotic systems. Next, the hash function is used to calculate the initial value of the chaotic system using a plaintext image. Then, we obtain a solution of this chaotic system and use the k-medoids clustering machine-learning algorithm and chaotic sequence to scramble the original image. Finally, new random numbers obtained using a chaotic signal and true random numbers are used to perform the exclusive-OR operator on the scrambled results. To illustrate the effectiveness of our method, a one-dimensional (1D) logistic chaotic system is selected for image encryption. The simulation results show that compared with the existing models, such as image encryption based on chaos and image encryption based on the advanced encryption standar (AES), our method is simpler with a higher security and resists different classical attacks.

Compared to 1D compressed sensing (CS), 2D CS is more efficient for compressing the plaintext image from two directions, but security level of current 2D CS-based ciphers is unsatisfactory. To solve this problem, this paper presents a novel color image compression and encryption algorithm by combining 2D CS, information entropy and chaos. Firstly, the color image is decomposed into red, green and blue components, then they are sparsely transformed by the discrete wavelet transform (DWT) to get three sparse matrices. Next, the obtained matrices are observed by two asymptotical deterministic random measurement matrices based on information entropy and counter (ADMMIC), which not only encrypts the plaintext image, but also compresses it in proportion to reduce the transmission bandwidth and storage space. Subsequently, the corresponding measurement value matrices are shuffled by a double random scrambling based on Arnold map and index vector (DRSAIV) to eliminate the correlation between adjacent pixels. Furthermore, the obtained permutated matrices are diffused by a simultaneous multiple random diffusion of inter–intra components (SMRDIC) to obtain the final cipher image, the plaintext pixel to be diffused, the key matrix involved in diffusion and the position of the obtained ciphertext pixel are all unpredictable, which makes statistical attack invalid. In addition, information entropy values of plaintext image are obtained to generate the initial values of the used chaotic systems, which greatly improve the ability to resist the known-plaintext and chosen-plaintext attacks. Simulation results and security analyses verify that this algorithm has good compression and high security.

This paper presents a novel encryption scheme based on genetic operations and Mixed Linear-Nonlinear Coupled Logistic Map Lattice (MLNCML) spatiotemporal chaotic system. The initial values of the MLNCML system are related to the plain-image. Therefore, this scheme is sensitive to the plaintext and keys. For the simplicity and efficiency of the encryption process, expanded XOR (eXOR) operation and genetic operations are applied in the scheme. Spatiotemporal chaotic system can resist dynamical degradation and periodic phenomena, which offers good randomness for encryption. Moreover, the eXOR operation in this paper can effectively avoid the chosen-plaintext attack of traditional XOR operation. The DNA mutation and crossover operations are controlled by chaotic sequences, which overcome man-in-the-middle attack in the traditional DNA addition and subtraction operation. The experimental results indicate that the proposed scheme has good security to resist common attacks.

In recent years, attribute-based encryption (ABE) provides a new idea to help researchers solving the problem of data privacy protection in cloud. But there are two issues in traditional ABE, the first issue is that the attributes in the access structures will be sent to users in cleartext together with the ciphertext. So a attacker has the opportunity to obtain some of the private information from the plaintext access structure. And the other issue is the traditional ABE scheme cannot revoke the users' illegal keys in an efficient way. To handle both of the above challenges, we come up with a large universe ciphertext-policy ABE (CP-ABE) scheme which supports partially hidden access structures (PHAS) and highly efficient key revocation at the same time in this paper. What's more, unlike most previous schemes, first our access structure is based on the expressive linear secret sharing scheme (LSSS) which supports both AND and OR gates in access formulas and second our scheme is built from the prime-order bilinear pairing groups. The comparison with other relevant works presents that our scheme is more comprehensive and efficient. Finally we rigorously prove and analyze that our scheme is selectively indistinguishable secure under chosen plaintext attacks (IND-CPA) in the random oracle model (ROM) and our access structure is really anonymous against off-line dictionary attacks.

In this paper, a new four-dimensional hyperchaotic system that has better unpredictability, more complex dynamic behavior, and a larger key space is proposed. The initial chaos value is calculated by using the Secure Hash Algorithm-512 (SHA-512) function, and the hyperchaotic sequence is then used as the key stream to encrypt the original image through pixel scrambling and pixel diffusion. The experimental results show that the image encryption algorithm has a strong ability to resist exhaustive attacks, statistical attacks and plaintext attacks.

In order to increase encryption capacity and improve transmission efficiency, this paper investigates an encryption scheme for multiple-image based on cascaded gyrator transforms and high-dimensional chaos. Firstly, each plainimage is converted into a real matrix through modulation, quaternion gyrator transform and sharing. The real matrices are connected in turn by plural coding and gyrator transforms. During the process of cascade, phase truncation and preservation operations are performed. The phase of the preceding transformation is modulated by that of the latter complex matrix to enhance security. Followed by splicing and scrambling, a real-valued ciphertext can be obtained. At the receiver end, all the plaintext images can be restituted by the reverse operation of the encryption process using the authorized keys. The adoption of high-dimensioanl chaos and Kronecker product further guarantees the security of the cryptosystem. The numerical results performed on 300 color images have demonstrated that the average PSNR of correctly decrypted images is up to 303.9939 dB, the NMSE is as low as 2.8024 × 10−28 and SSIM is equal to 1.0000. The analysis of sensitivity, statistical characteristic and robustness proves the feasibility and relibility of the proposed encryption scheme.

In recent years, people have put forward various image encryption algorithms based on pixel level. In fact, bit level encryption has better effect than pixel level encryption. Therefore, this paper proposes a new bit-level image encryption algorithm based on Back Propagation (BP) neural network and Gray code. Firstly, the plaintext image is conversioned into binary image, then, the hyperchaotic Lorentz system is used to generate two sets of chaotic sequences for the Gray code bit-level permutation operation to generate the permutation matrix. Secondly, the permutation matrix is converted into a bit matrix reverse order output to generate a diffusion matrix. Finally, the algorithm uses a BP neural network composed of Logistic map and Piece-Wise Linear Chaotic (PWLCM) map to generate a key stream. The key stream is xored with the diffusion matrix to generate a ciphertext matrix. The experimental results show that the algorithm improves the encryption efficiency, has good security and can resist common attack methods.

A modified XXTEA “M-XXTEA” symmetric block cipher that has a simple construction compared to the advanced encryption standard (AES) is proposed. It is efficient for protecting limited-resource devices such as IoT smart devices. The M-XXTEA will be able to achieve confidentiality during transmission of data over the internet. Since the original XXTEA was vulnerable against key-related and chosen-plaintext attacks. Therefore, this paper introduces a new and robust version of the original XXTEA by employing an improved S-box to enhance security to overcome such types of attacks. Besides, the M-XXTEA is coupled with a chaotic key generator system adding a layer of security achieving the idea behind the one-time pad. The cipher keys are dynamically changing for each block of plaintext when encrypted. Thus, it provides a more robust security mechanism than the original XXTEA and the AES. Besides enhancing data security, the M-XXTEA can function with different sizes of text blocks and with different key sizes. Several experiments are implemented to compare the performance of the M-XXTEA with the original XXTEA and with the AES. Results show that the M-XXTEA encryption and decryption time efficiencies outperform AES by 60%. Besides, the M-XXTEA achieves speed efficiency 57% better than the AES. It can be used efficiently for protecting IoT smart devices in the industry, and e-health systems, and smart cities.

In this paper, in order to solve the problem of un-rigorous scrambling method and single diffusion method in image encryption, a new method based on arithmetic sequence scrambling model, DNA coding sequence and one-dimensional Logistic mapping is proposed. First, the Hash array is obtained by combining the information of the original plaintext image with the Hash algorithm SHA-512. The Hash array generates the initial value and control parameters of the chaotic system, and then generates the chaotic key flow. Second, the arithmetic progression of partitioned matrix after scrambling, change the position of the original image pixels, replacement and operation, and then for DNA combines images and the chaotic sequence of chaotic system to produce DNA, DNA encoding, decoding rules for operation, change the original data bits of pixel values, thus further destruction of the original information. Finally, a chaotic diffusion operation is performed to further change the pixel information of the original image and output the cipher-text image. The experimental results and various security analyses show that the algorithm has good encryption effect and can resist the common plaintext attack, clipping attack and noise attack. The algorithm can be used for image encryption.

This paper introduces an image encryption algorithm shorted as CITSPD, manipulated by circle index table scrambling and partition diffusion. Firstly, the circle index table is obtained through the generation, circle shift and transposition of the benchmark sequence. Secondly, the plain image is transformed into the wavelet coefficient and is then scrambled by the circle index table. Thirdly, the permutated image is disturbed by different noises and is further divided into four subsections. Finally, the forward and inverse partition diffusions are performed to the subsections for getting the cipher image. The main feature of this algorithm is that the robust chaos-based keystream and encryption process are highly sensitive to the plaintext, which will effectively resist against chosen-plaintext and known-plaintext attacks. In addition, the encryption scheme is free of noise attack since the inverse diffusion differs from the forward one. And the diffusion effect can be effectively enhanced by, as much as possible, increasing the small pixel value and decreasing the large pixel value. Experimental tests and security analyses are carried out to verify the advantages of the scheme.

Based on the n-ary counting system, combined with the matrix semi-tensor product theory and Hilbert curve, a chaotic image encryption algorithm is designed. Different from the traditional encryption method, the algorithm proposed in this paper is an encryption algorithm with scrambling and diffusion at the same time. First, the pixel value is converted from decimal to n-ary. In the n-ary counting system, the plaintext image is randomly divided into some groups, and the Hilbert curve is used for scrambling to each group. The blocks are converted into scrambled images, so that the scrambling and diffusion can be carried out at the same time. Then, in order to improve the security of the algorithm, another round of diffusion is carried out based on matrix semi-tensor product mechanism. Chaotic sequence is generated by Chen system. This chaotic sequence performs matrix semi-tensor product operation with the first round of encrypted image, and generate second encrypted images. Finally, this encryption method is applied to color image encryption. Compared with some representative algorithms, the experimental results show that the algorithm proposed in this paper is secure and it can resist common attacks.

This paper proposes improved algebraic attacks that are effective for lightweight block ciphers. Concretely, we propose a new framework that leverages on algebraic preprocessing as well as modern SAT solvers to perform algebraic cryptanalysis on block ciphers. By combining with chosen plaintext attacks, we show that our framework can be applied to lightweight block ciphers that exhibit a nice differential trail. In particular, we demonstrate our techniques by performing algebraic cryptanalysis on both the Present cipher and the Simon cipher. For the Present cipher, we successfully solved up to 9 rounds with at most 32 key bits fixed and 8 chosen plaintexts. On the other hand, for the Simon cipher, we tested our method on Simon-32/64 and Simon-64/128. For these two versions, our attack can solve up to 13 rounds with only 8 chosen plaintexts by fixing 4 and 6 key bits for Simon-32/64 and Simon-64/128, respectively. Further, by considering a class of weak keys, we can extend our attacks to 16 rounds. As far as we are aware, these are the best algebraic attacks on these ciphers in the literature.

This paper introduces a double image encryption scheme mainly based on symmetry of two-dimensional discrete Fourier transform (2D-DFT) and equal modulus decomposition (EMD). Firstly, the plural form is adopted to encode double image as a whole and the 2D-DFT is performed. To obtain matrices satisfying property of conjugate symmetry, the spectra are implemented addition and subtraction. Followed by truncation-superposition operations, another complex value matrix is attained and equal modulus decomposition is carried out to get two phase templates, which are further gyrator transformed to enhance security. With an orthogonal matrix, the real and imaginary parts are shared and spliced together to produce a real-valued cipherimage, which aims to make storage and transmission convenient. The initial states of 2D logistic map are closely related to the plaintext images and is employed to generate phase mask, rotation angles as well as the input of Gaussian matrix, which ensures the high level of security. Experimental results have demonstrated the feasibility and validity of the proposal in restituting plaintext images, security and resisting Gaussian noise attack.

Based on the deoxyribonucleic acid (DNA) sequence operations and chaotic systems, a novel improved color image encryption algorithm is presented with one-time-pad. Three DNA matrices are obtained by DNA encoding the plain-image firstly. To enhance the proposed algorithm’s robustness of resisting known-plaintext and chosen-plaintext attacks, the key streams, which are used to scramble the positions of the three DNA matrices, are generated from 3D skew tent map (3D-STM) by using the secret keys and the hamming distances between the DNA matrices. Then, we perform the DNA XOR, addition and subtraction operations on the DNA matrices and the key streams to get the cipher-image. At this stage, we also update the initial values of the coupled map lattice (CML) by the circle distance of DNA matrices obtained from the previous step to further enhance the proposed algorithm’s ability of resisting plaintext attack. Finally, we get the encrypted color image by decoding DNA matrices. The simulation and security analysis show that the proposed algorithm has an extraordinary ability to resist plaintext attack, differential attack and statistical attack, etc.

Design principles for image encryption schemes abound in the literature. Among these schemes, few were built upon the philosophy of swapping of the pixels in the given input image. Swapping is a very straightforward and a naive approach for image scrambling. We believe that fuller potential of swapping has not been realized yet. In this work, a novel image encryption scheme is being presented through the swapping of pixel values of the given gray scale input image. The 5D multi-wing hyperchaotic system rendering five key streams of random numbers have been used in the proposed cipher. After the gray scale image is input, its pixels are swapped randomly. The random numbers given through the first two key streams jointly determine the address of the first pixel to be swapped with the second pixel whose address is determined by the random numbers given through the third and fourth key streams. In this way, the pixels of the given image are swapped abundantly. The selection of both the pixels for swapping is purely arbitrary and random in character having no restriction of linearity and sequentiality as was done by other schemes previously. To create the diffusion effects, an XOR operation is carried out between this scrambled image and the key image formed through the fifth stream of random numbers given by the chaotic system. SHA-384 hash codes have been used in the proposed scheme to embed the plaintext sensitivity. The simulation and the extensive security analyses carried out at the end expressly portray the good security effects and the potential for the real world application of the reported scheme.

This paper presents a novel image compression-encryption scheme, which has the compression-confusion-diffusion Structure. Firstly, based on Chebyshev chaotic map, a Gauss measurement matrix is constructed and optimized, which is applied to compressive sensing. Then, an image compression-encryption algorithm is proposed by using a six-dimensional discrete chaotic map. In the proposed scheme, the original image is transformed into a sparse coefficient matrix by discrete wavelet transform, and the sparse coefficients are measured by using the optimized Gauss measurement matrix to get the measured values. Then, the measured values are quantized into integer values and the compressed image is obtained. Furtherly, the compressed image is encrypted by using a six-dimensional chaotic map. In the process of encryption, the plaintext image is divided into two parts, when encrypting the second part, the first part is used as part of the key. While encrypting the first part, the ciphertext of the second part is used as part of the key. Thus, the algorithm has strong confusion and diffusion effect and makes ciphertext sensitive to plaintext. Experimental results such as effects of compression-encryption, key space analysis, key sensitivity analysis, differential analysis, histograms analysis, information entropy analysis, and correlation coefficients analysis show that the proposed scheme is secure and has high application potential.

The traditional design of voice collector has poor anti attack ability, which makes the encryption effect of voice transmission poor. Therefore, taking the mobile network voice collector as the research object, 3des-ecc algorithm is applied to the information transmission encryption of the mobile network voice collector.An improved speech signal collector is designed, which combines 3DES and ECC algorithm to realize the encryption of speech transmission information. An improved voice signal collector is designed, which combines 3DES and ECC algorithm to realize the encryption of voice transmission information. In the process of encryption, 168-bit random key is generated first, and it is grouped according to 56 bits as 3DES key, and then the plaintext is encrypted by the key to generate ciphertext; the random key is encrypted by ECC public key of the receiver. The experimental results show that the encryption time of this method is less than 1 s, the data integrity is 93%, and the data loss rate is only 0.33%. It has better anti attack ability, fast encryption speed and good encryption effect.

This paper presents a digital image encryption scheme based on multi chaotic system and random DNA coding. Firstly, the initial values and parameter values of 2D Logistic-adjusted-Sine mapping (2D-LASM) and Logistic-Sine system (LSS) are obtained from SHA256 hash values of the original image. In the scrambling stage, the chaotic sequences generated by 2D-LASM are used to get two column scrambling matrices and row scrambling matrix, respectively. The elements of the second column scrambling matrix and row scrambling matrix are used as row and column coordinates in the scrambling process. Then apply it to scrambling the DNA encoded image, which can complete the row and column scrambling at the same time. In the diffusion stage, we proposed a new diffusion method. Through the chaotic sequence generated by the LSS, a DNA coding sequence is obtained. DNA XOR operation is carried out on the central point and horizontal line of the image, and then spread from the central line to the upper and lower directions of the matrix to achieve the purpose of multi-directional diffusion and improve the encryption efficiency. Experimental results and security analysis show that the algorithm executes fast and has strong security. It can resist many attacks, such as statistical attacks, brute attacks, plaintext / select plaintext attacks, etc.

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.

Over the last few years, lots of chaotic image encryption schemes have been proposed. However, most of the schemes are permutation-diffusion architectures which still have some shortcomings, such as weak key streams, small key spaces, small information entropy, and so on. To eliminate the above weaknesses, in this paper, we propose a hyper-chaotic image encryption scheme based on quantum genetic algorithm (QGA) and compressive sensing (CS), which is a new image encryption scheme and has not been proposed so far. Firstly, QGA can update the population with the quantum rotation gate, which can enhance the randomness of the population and avoid falling into local optimum. Then compressive sensing technology is used to reduce data storage and speed up the encryption and decryption process. Moreover, we utilize the SHA-512 hash function of the plain image to calculate the initial values of the hyper-chaotic system, which is capable of enhancing the relationships between encryption schemes and plain images. The simulation experiments and security analysis reveal that the proposed scheme is more efficient in resisting statistical attack and plaintext attack and shows better performance in peak signal-to-noise ratio (PSNR) and information entropy compared with other image encryption schemes based on chaos theory.

Recently, a color image encryption scheme based on the Sine-Sine chaotic system has been proposed by Wang et al. (Signal Processing 144:444–452, 2018). In their scheme, a private parameter E is defined based on global plain information in hope of resisting the chosen-plaintext attack. However, we find that the private parameter is dependent purely on average intensity of a plain image, thereby leaving an open door for cryptanalysis. In this paper, we propose a collision-based inference algorithm to effectively break Wang’s image cipher. Then, in order to enhance the security, we develop a hash-based cryptosystem under the permutation-and-diffusion architecture. We conduct experiments and perform extensive comparative studies.The qualitative and quantitative results demonstrate the effectiveness of the collision-based inference algorithm, and the superiority of the proposed image cipher especially in terms of plaintext sensitivity.

Proxy re-encryption (PRE) is a public-key cryptography primitive that delegates the decryption capabilities of a user (called delegator) to another user (called delegatee) using a re-encryption key. A semi-trusted proxy uses the re-encryption key to transform a ciphertext under the delegator’s public key such that it becomes a ciphertext under the delegatee’s public key. If instead of “all”, a delegator wishes to delegate a subset of his decryption capabilities, there is a need for elevating the level of trust in the re-encrypting proxy. As a result, PRE in multi-proxy scenario has received significant research attention in recent times. In this paper, we introduce a new PRE primitive in a multi-proxy setting called Threshold Progressive Proxy Re-encryption (TP-PRE), that involves progressive transformation of ciphertext and results in production of a valid re-encrypted ciphertext if and only if at least t out of the total N distinct proxies perform re-encryption. The way these proxies are selected for re-encryption is significantly different from the existing threshold proxy cryptosystems. The TP-PRE scheme we present does not require prior knowledge about the available proxies. Proxies can take turn in any order to progressively transform the ciphertext and output of $$t{\mathrm{th}}$$ transformation, or any transformation(s) afterward, is the final re-encrypted ciphertext that can be successfully decrypted by the intended delegatee to obtain the correct underlying plaintext. Unlike conventional threshold cryptosystems, TP-PRE does not have a share combination phase hence it does not require any central dealer. We formally define system model and security notions for TP-PRE. We present a concrete construction for TP-PRE that satisfies indistinguishability under chosen-plaintext attacks (IND-CPA) and formally prove its security. We analyze the performance of our construction by providing theoretical bounds of the solution along with the results of practical implementation.

In this paper, we find that compressive sensing (CS) with the chaotic measurement matrix has a strong sensitivity to plaintext. Because of the quantification executed after CS, however, the plaintext sensitivity produced by CS may be weakened greatly. Thus, we propose a novel CS-based compression-encryption framework (CS-CEF) using the intrinsic property of CS to provide a strong plaintext sensitivity for the compression-encryption scheme, which takes a low additional computation cost. Meanwhile, a simple and efficient Substitution box (S-box) construction algorithm (SbCA) based on chaos is designed. Compared with the existing S-box construction methods, the simulation results prove that the proposed S-box has stronger cryptographic characteristics. Based on the above works, we develop an efficient and secure image compression-encryption scheme using S-box (CSb-CES) under the proposed CS-CEF. The simulations and security analysis illustrate that the proposed CSb-CES has the higher efficiency and security compared with the several state-of-the-art CS-based compression-encryption schemes.

Attribute-based encryption (ABE) is a powerful cryptographic primitive for access control and fine-grained sharing on encrypted data. Due to this functionality, ABE is usually adopted in encrypted cloud storage for flexible data sharing. However, the main drawback of ABE is that the computational cost grows linearly with the complexity of the access policy. One of the promising solutions for the problem is to outsource computation securely. For example, the user can outsource most of the decryption cost to a proxy, while the underlying plaintext remains confidential. Nonetheless, all the existing ABE schemes with outsourced decryption ignore the fairness between the user and the proxy, i.e., the user may refuse to pay even if he/she obtain the valid result. To address this problem, in this paper we propose a new ABE scheme with fair outsourced decryption by using blockchain and sampling technique. In particular, we make use of the smart contract in blockchain to guarantee that the proxy can always get the reward with the valid outsourced decryption result. Furthermore, we apply the sampling technique to enable the miners in blockchain to check the validity of the outsourced decryption result. The detailed analysis conducts that our proposal is secure and fair under some reasonable assumptions, and the experimental results demonstrate that our proposal is efficient. At last, it may be of independent interest that our proposal is a generic construction for pairing-based ABE schemes.

Cloud data storage is a service offered by cloud computing for storing the data. Though it has a lot of benefits, the security of the stored data is one of its major concerns. Many models have been developed to address this issue. These models encrypt the data and store them. Advanced encryption standard (AES) is one of the encryption methods that has been used prevalently. This paper presents a model that tries to further strengthen the AES algorithm. It alters the shift row of the AES by making it key dependent. The key dependency enhances the security of the algorithm and the results show that the statistical pattern of the plaintext is dispersed over the cipher text, thereby, defending the plaintext from the cryptanalysis. Experimental results indicate that the dispersion ratio of the plaintext over the cipher text increases from 0.75 for AES to approximately 1 for the proposed model. The model is also analyzed using the coefficient of variation metric. The proposed model also exhibits a significant level of avalanche effect.

In 2017, an efficient chaotic image cipher with dynamic lookup table driven by bit-level permutation strategy (ICDLT) was proposed (Hu et al. Nonlinear Dyn 87:1359–1375). The chaotic cipher adopts a plaintext-related image encryption mechanism as an efficient measure against chosen-plaintext/ciphertext attack. ICDLT is composed of four basic parts: inter-pixel permutation, sequential addition, intra-pixel permutation and diffusion processes, where two kinds of permutation are both related to the plaintext. Although ICDLT is built on complex nonlinear dynamics, we found that it is still vulnerable against chosen-plaintext attack and its individual sub-keys can be recovered using a divide-and-conquer strategy. Benefiting from the essential structure of ICDLT and the intrinsic properties of Latin square, the proposed attack requires only $$ (8 \cdot N^2 +256 + n_c \cdot (2 \cdot N -1))$$ plain images, where $$N^2$$ is the size of the image and $$n_c$$ is the number of cipher images that need to be cracked. Furthermore, we summarize a more general framework which is beneficial for cryptanalyzing a class of plaintext-related image ciphers. Finally, we propose an improved scheme based on the designed plaintext-related XOR encryption (PR-XOR) module to enhance the security of ICDLT. Theoretical analysis and experiments prove that the improved scheme not only maintains the excellent statistical performances of the original one, but also can resist various attacks.

In terms of application of the generalized BKW algorithm, the estimates of security of Ring-LWE symmetric cryptosystem against chosen plaintext attack have been obtained. These estimates allow us to select cryptosystem parameters directly, based on its security requirements against known chosen plaintext attacks. Applicability of the generalized BKW algorithm is an important factor that affects cryptosystem security against such attacks.

Recently, Kim et al. proposed a modified Dual-Ouroboros public-key encryption ($${\textsf{PKE}}$$) using Gabidulin codes to overcome the limitation of having decryption failure in the original Dual-Ouroboros using low rank parity check codes. This modified Dual-Ouroboros $${\textsf{PKE}}$$ using Gabidulin codes is proved to be IND–CPA secure, with very compact public key size of 738 bytes achieving 128-bit security level. However, they did not specify on their choice of the secret key S used in their $${\textsf{PKE}}$$. In this paper, we analyze different possible choices for S in the modified Dual-Ouroboros $${\textsf{PKE}}$$ using Gabidulin codes. More specifically, we show that if S is invertible over $${\mathbb{F}}_{q^m}$$ without any restriction, then the decryption algorithm will fail. Furthermore, we show that Kim et al.’s proposal of the modified Dual-Ouroboros $${\textsf{PKE}}$$ using Gabidulin codes has secret key S over $${\mathbb{F}}_q$$ for its decryption algorithm to be correct. Then, we proposed two attacks: key recovery attack and plaintext recovery attack on their $${\textsf{PKE}}$$ with S over $${\mathbb{F}}_q$$. We are able to recover the secret key for all the proposed parameters within 235 seconds. Moreover, we show that the public key matrix in their proposal generates a subcode of Gabidulin code. As a consequence, we can apply the Frobenius weak attack on their proposal and recover the plaintext for all the proposed paramters within 0.614 second. Finally, we give a proposal for the modified Dual-Ouroboros $${\textsf{PKE}}$$ using Gabidulin codes such that it is correct and secure, by considering certain restrictions on S over $${\mathbb{F}}_{q^m}$$.

In order to realize the secure transmission of the H.264 compressed video bitstream, a detailed analysis of the structure for video bitstream is performed. The parameter set and frame header data related to video decoding are retained, and the slice data payload in the network abstraction layer unit is selected as the encryption object. The video format is compliant under the premise of real time and security. The novel cross-coupled chaotic system is designed as the key stream generation component, and the key stream is closely related to the plaintext through the synchronization vector mechanism. When part of the ciphertext stream is lost, the subsequent units can still be decrypted normally, which solves the problem of robustness encryption and decryption for video stream based on chaotic cipher. Detailed performance testing and security analysis data show that the proposed scheme has obvious advantages over existing research in terms of time overhead, compression ratio, anti-chosen-plaintext attack and robustness.

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.

In this paper, an enhanced honey encryption (HE) scheme for reinforcing the security of instant messaging systems and confounding the time and resources of malicious persons is presented. HE offers security beyond the brute-force bound by yielding plausible-looking but fake plaintext upon decryption with an incorrect key. Recent developments have seen the application of HE in the security of specific real-world systems, such as passwords and credit cards. However, applying the HE scheme to address other economic problems remains a daunting task as it requires modifying the HE algorithm to fit into the problem-in-view. For instance, applying the scheme for robust transmission of chat-messages upon decryption with an incorrect key will demand to generate contextually correct, valid-looking but fake chat-message which is indistinguishable from a human-generated message. This paper enhances the HE scheme by leveraging natural language processing techniques to build semantically plausible but fake chat-messages which will be served to the adversary during his attacks. Findings from evaluations reveal that the novel system is resilient to eavesdropping as an adversary is unable to distinguish decoy messages from the plaintext upon decryption with an incorrect key.

The progress in communication and hardware technology increases the computational capabilities of personal devices. Aggregators, acting as third parties, are interested in learning a statistical function as the sum over a census of data. Users are reluctant to reveal their information in cleartext, since it is treated as personal sensitive information. The paradoxical paradigm of preserving the privacy of individual data while granting an untrusted third party to learn in cleartext a function thereof, is partially addressed by the current privacy-preserving aggregation protocols. Current solutions are either focused on an honest-but-curious Aggregator who is trusted to follow the rules of the protocol or model a malicious Aggregator with trustworthy users. In this paper, we are the first to propose a protocol with fully malicious users who collude with a malicious Aggregator in order to forge a message of a trusted user. We introduce the new cryptographic primitive of convertible tag, that consists of a two-layer authentication tag. Users first tag their data with their secret key and then an untrusted Converter converts the first layer tags in a second layer. The final tags allow the Aggregator to produce a proof for the correctness of a computation over users’ data. Security and privacy of the scheme is preserved against the Converter and the Aggregator, under the notions of Aggregator obliviousness and Aggregate unforgeability security definitions, augmented with malicious users. Our protocol is provably secure, and experimental evaluations demonstrate its practicality.

Data aggregation can effectively improve resource utilization in Internet of Vehicles (IoV), and has attracted broad attention recently. However, because of the particularity of nodes in IoV, data aggregation faces security challenges such as location privacy, data privacy and accuracy of aggregation results. To solve these challenges, in this paper, we propose a secure and lightweight privacy-preserving data aggregation scheme, named SLPDA, for IoV. Specifically, SLPDA employs Chinese Remainder Theorem to map multi-dimensional data to one-dimensional data, and uses masking technology to encrypt data, thus roadside units can realize lightweight data aggregation without plaintext. SLPDA also adopts Identity-based batch authentication technology to reduce authentication overhead. Detailed security analysis indicates that SLPDA can resist various security threats. In addition, the performance evaluations demonstrate that SLPDA is more efficient than the reported schemes in terms of computation complexity and communication overhead.

An advanced image encryption scheme should equip the capability against malicious attacks, reduce the losses under attacks, and improve the compression rate tremendously due to the unsafe network environment and the limited bandwidth resources. Recently, compressive sensing (CS) has been introduced into image encryption schemes because of the merit of low sampling rate. However, these schemes still cannot address the above requirements well. In order to improve compression rate while providing higher security level, a novel subdata image cryptosystem is proposed by introducing vector quantization (VQ) into CS-based encryption scheme. The plaintext image is first divided into VQ index blocks and the error compensations that are sparse enough to be compressed by CS. Then, the index information and CS measurements are further scrambled and diffused by chaotic sequences to achieve enhanced security. It can be ensured that the primary index information is informative and occupies smaller proportion of cipher image such that it cannot be easily tampered if only a part of the image is attacked. In contrast, the secondary error information is a good supplement to the former and occupies larger proportion. Simulation results verify that our proposed scheme has overwhelming compression rate and security effect to resist malicious attacks when compared with the state-of-art schemes. In addition, even if the important information is damaged, the destroyed pixels can be located and the plaintext image can be reconstructed with VQ neighbor indexes.

Quite recently, Luo and Wan putted forward a new certificateless signcryption (CLSC) scheme with low computation cost in the standard model. They stated that their newly proposed scheme achieves the unforgeability against adaptive chosen message attack (i.e, unforgeability) and indistinguishability against adaptive chosen ciphertext attack (i.e., confidentiality). However, we find that the scheme cannot reach the claimed security feature. Specifically, in this paper, we will demonstrate that in Luo and Wan’s CLSC scheme, the plaintext can be easily recovered from the ciphertext by ordinary attacker and malicious-but-passive KGC. In addition, we identify that this scheme even cannot resist forgery attack of a malicious KGC.

The ultimate goal of modern cryptography is to protect the information resource and make it absolutely unbreakable and beyond compromise. However, throughout the history of cryptography, thousands of cryptosystems emerged and believed to be invincible and yet attackers were able to break and compromise their security. The main objective of this paper is to design a robust cryptosystem that will be suitable to be implemented in Internet of Things. The proposed cryptosystem is based on algebraic geometric curves, more specifically on Hermitian curves. The new cryptosystem design is called Hermitian-based cryptosystem (HBC). During the development of the HBC design, Kerckhoffs’s desideratum was the main guidance principle, which has been satisfied by choosing the Hermitian curves as the core of the proposed design. The proposed HBC inherits all the advantageous characteristics of Hermitian curve which are large number of points that satisfy the curve and high genus curves. The aforementioned characteristics play a crucial role in generating a large size encryption key for HBC and determine the block size of plaintext. Due to the fact that HBC used algebraic geometric codes over Hermitian curve, it has the ability to perform error correction in addition to data encryption. The error correction is another advantage of HBC compared with many existing cryptosystems such as McEliece cryptosystem. The number of errors that can be corrected by HBC is larger (high data rate) than other algebraic geometric codes such as elliptic and hyperelliptic curves. It also uses non-binary representation which increases its attack resistance. In this paper, the proposed HBC has been mathematically compared with elliptic curve cryptosystem. The results show that HBC has many advantages over the elliptic curves in terms of number of points and genus of the curve.

The internet of things (IoT) is now an in-demand technology that has been adopted in various applications and includes various embedded devices, sensors and other objects connected to the Internet. Due to the rapid development of this technology, it covers a significant portion of the research interests nowadays. IoT devices are typically designed for collecting different types of data from various sources and transmitting them in digitized form. However, data security is the burning issue in the IoT technology, which can broadly impact the privacy of crucial data. In this regard, a new lightweight encryption method called LRBC has been proposed in this work for resource constraint IoT devices which can provide data security at the sensing level. The LRBC has used the structural advantages of both substitution–permutation network (SPN) and Feistel structure together to achieve better security. Furthermore, the proposed method has been tested on NEXYS 4 DDR FPGA (Artix-7) trainer kit and implemented for application specific integrated circuit (ASIC) chip on TSMC 65 nm technology. The proposed algorithm consumes very less power of 11.40 μW and occupies a 258.9 GE (Gate Equivalent) area. Besides, a thorough security analysis shows that the proposed scheme ensures high security against various attacks with robustness. Moreover, the average avalanche effect of LRBC is found to be 58% and 55.75% concerning plaintext and key, respectively.

Deduplication eliminates duplicated data copies and reduces storage costs of cloud service providers. However, deduplication of encrypted data is difficult. Current solutions rely heavily on trusted third parties, and does not recognize the popularity of data, resulting in unsatisfying security and efficiency. A secure encrypted data deduplication scheme based on data popularity is proposed. Tags are calculated via bilinear mapping to determine whether different encrypted data originate from the same plaintext. Ciphertext policy attribute-based encryption is used to protect the tags. A secure key delivery scheme is designed to pass the data encryption key from an initial data uploader to subsequent uploaders via the cloud server in an offline manner. The cloud server can perform deduplication without the assistance of any online third party. Security analysis and simulation experiments are provided, proving the practicability and efficiency of the proposed scheme.

Several successful cache-based attacks have provided strong impetus for developing side channel resistant software implementations of AES. One of the best-known countermeasures—use of a “minimalist” 256-byte look-up table—has been employed in the latest (assembly language) versions. Software and hardware pre-fetching and out-of-order execution in modern processors have served to further shrink the attack surface. Despite these odds, we devise and implement two strategies to retrieve the complete AES key. The first uses adaptively chosen plaintext and random plaintext in a 2-round attack. The second strategy employs only about 50 blocks of random plaintext in a novel single round attack. The attack can be extended to spying on table accesses during decryption in a ciphertext-only attack. We also present an analytical model to explain the effect of false positives and false negatives and capture various practical tradeoffs involving number of blocks of plaintext, offline computation time for key retrieval and success probability.