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When visual sensor networks (VSNs) enter daily life in society, they not only bring great convenience but also cause people to worry about privacy. Traditional image encryption uses the snowflake effect to protect the privacy, but this can compromise the usability of directly browsing images captured by nodes in VSNs. Recently, thumbnail-preserving encryption (TPE) has been proposed to balance image usability and privacy. However, the Markov chain's limited connectivity and high time cost, which result in low efficiency, may preclude its application in VSNs. Motivated by this, we propose a novel TPE scheme to protect the image collected in VSNs' privacy efficiently. We first deeply study the bijective relationship between the three-pixel group and its rank, and then propose a new number method for both, based on which we design the efficient rank mapping. Subsequently, an efficient thumbnail-preserving image encryption via three-pixel rank mapping (E-TPE) is designed, achieving NR security and enhancing the Markov chain's connectivity. The experiments demonstrate the scheme's efficiency; that is, it is currently the quickest ideal-TPE scheme with NR security, and a good balance is achieved between usability and privacy. [ABSTRACT FROM AUTHOR]

Privacy concerns may be caused after uploading images into image hosting platforms. For traditional image encryption, images with rich content and meaning are transformed into noise-like encrypted images without any visual information, which can protect privacy from infringement but at the expense of visual usability. Recently, thumbnail-preserving encryption (TPE) was proposed to balance privacy and usability by preserving the thumbnail unchanged after encrypting. On the other hand, a large number of pseudo-random functions with high computational complexity are utilized in the existing TPE schemes, which makes the encryption and decryption time too long. Motivated by this, we deeply analyze the characteristics of TPE and propose a scheme to organically combine TPE with chaotic systems, which reduces the encryption and decryption time exponentially besides ensuring security. The experiments show that the time cost is reduced dozens of times as well as relatively stable compared with the existing schemes. Meanwhile, encrypted images have high visual quality and can resist some commonly used attacks including differential attack and face detection and the balance between privacy and visual usability is achieved. [ABSTRACT FROM AUTHOR]

With the popularity of cloud storage services, people are increasingly accustomed to storing images in the cloud. However, cloud storage services raise privacy concerns, e.g., leakage of images to unauthorized third parties and service providers may exploit image detection technologies to portrait users without permission. Although privacy concerns can be solved by encrypting images before they are uploaded to the cloud, traditional encryption methods significantly affect the usability and user experience, for example, users cannot preview images in the cloud. Recently, Marohn et al. proposed two approximate thumbnail-preserving encryption schemes, called DRPE and TPE-LSB, to balance the privacy and usability of images in the cloud. However, both schemes have defects that either the decryption may fail or the ciphertext images have poor performance in perceived quality and too many noise points after decryption. To this end, we pertinently propose a high-fidelity thumbnail-preserving encryption scheme (HF-TPE). Compared with the previous works, on the one hand, the HF-TPE scheme not only ensures the correct decryption of ciphertext images, but also makes the ciphertext thumbnails more close to the plaintext images perceptually. On the other hand, the decrypted thumbnails have lower noise intensity and upper limit of the number of noises. In addition, simulation experiments further show that the HF-TPE scheme can guarantee users’ usability. [ABSTRACT FROM AUTHOR]

Control parameters play a key role in a chaotic system, where they directly determine its chaotic performance. In this brief, we propose a novel parameter-selection-based chaotic system (PSCS), where a new sequence of control parameters is generated using Kolmogorov entropy (KE). KE measures the chaotic behaviors of a chaotic system, and the positive values indicate that the system exhibits chaotic characteristics. Hence, the new sequence is formed by the parameters that yield positive KE values, which always maintain the chaotic behaviors in each iteration. Coupling the obtained sequence into a basic chaotic map, PSCS achieves a simple structure and lower computation cost. Experiments on the time complexity, NIST SP800-22 test suit, and information entropy demonstrate the good performance of the proposed PSCS. [ABSTRACT FROM AUTHOR]

To improve the randomicity behaviors of some existing chaotic maps, this paper proposes two integrated chaotic systems (ICS), which conduct cascade, nonlinear combination, and switch operations to three basic 1D chaotic maps to generate new structures. The developed systems are able to yield several more complicated chaotic maps. Compared with several existing maps, the newly-generated ones have more advanced properties, including wider chaotic ranges, and more complex chaotic behaviors. To demonstrate the effectiveness of ICS, we also design an image encryption scheme based on ICS. Simulation results on different types of images and extensive security analysis demonstrate that the proposed approach has satisfactory properties in image encryption. [ABSTRACT FROM AUTHOR]

With the increasing value of 3D mesh in the economic, social, commercial, and defense sectors, its security is becoming increasingly important. Meanwhile, the 3D mesh may be distributed to people with different security levels, for whom the mesh should present a differentiated visual effect. Recently, some researchers have proposed one encrypted scheme that can meet the above requirements; however, the scheme is complex and time costly. Motivated by this, we analyze the structure of the 3D mesh and the features of the scheme with differentiated visual effects. A novel encryption framework (XOR-permutation) combined with the chaotic system is constructed to encrypt 3D meshes, which achieves the differentiated visual effects and reduces the time cost. Experiments show that the proposed scheme is enough security and the time cost with the previous work is more than ten or tens of times higher than the proposed scheme. • This scheme achieves the ability to present differentiated visual effects after decryption. • A novel encryption framework is proposed for differentiated visual effects of 3D meshes. • It greatly simplifies the encryption process and reduces the time cost. [ABSTRACT FROM AUTHOR]

With the popularity of cloud servers, an increasing number of people are willing to store their images in the cloud due to many conveniences such as online browsing and managing images. On the other hand, this inevitably causes users' concerns about image privacy leakage. Many image encryption schemes are proposed to prevent privacy leakage, while most of them focus only on privacy protection and ignore the usability of encrypted images. For this purpose, Marohn et al. (2017) designed two approximate thumbnail-preserving encryption (TPE) schemes to balance image privacy and usability. However, the decrypted image in these two schemes are only perceptually close to the original one and the original image cannot be perfectly recovered. To this end, we design a perfectly recoverable approximate TPE scheme in this paper, which combines reversibledata hiding (RDH) with encryption schemes. The thumbnails of the original and processed images are similar to balance image privacy and usability well. Meanwhile, the reversibility of RDH and encryption schemes is utilized to ensure the perfect recoverability in the proposed scheme. Experiments show that the proposed approximate TPE scheme is no longer limited to balancing usability and privacy but attains perfect recovery. [ABSTRACT FROM AUTHOR]

• The proposed TPE2 is the first to extend the exact TPE as a group of three pixels. • The TPE2 is compatible with existing cloud storage services. • Results show a good balance between image usability and privacy. Facing a large number of personal images and local devices with limited resources, the cloud service plays an increasingly important role in image storage. However, there is no doubt that this will raise a lot of privacy concerns if the image is not under the direct control of the owner. Simply encrypting images utilizing traditional encryption schemes protects the privacy of them, but it sacrifices the usability of image content. Resolving the tension between the usability and privacy risks of images is a critical issue for users. Recently, Tajik et al. proposed the exact thumbnail preserving image encryption (TPE) scheme as a group of two pixels to balance image privacy and usability in the cloud. However, the scheme utilizes the Markov chain to prove the security. The fewer pixels in the group, the worse the connectivity of the chain state. Motivated by this, we further extend the TPE scheme to propose a three-pixel exact TPE scheme, called TPE2. The scheme achieves exact TPE as a group of three pixels. The experimental evaluations show that the image encrypted by the scheme has a good image quality and a satisfactory balance usability and privacy. [ABSTRACT FROM AUTHOR]