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![Example of negative-positive transformation when using conventional scheme [5] where {x R , x G , x B } = {255, 255, 255}.](profile/Shoko-Imaizumi/publication/329349861/figure/fig2/AS:699092774682625@1543688114142/Example-of-negative-positive-transformation-when-using-conventional-scheme-5-where-x-R.png)
Example of negative-positive transformation when using conventional scheme [5] where {x R , x G , x B } = {255, 255, 255}.
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This paper proposes a block-permutation-based encryption (BPBE) scheme for the encryption-then-compression (ETC) system that enhances the color scrambling. A BPBE image can be obtained through four processes, positional scrambling, block rotation/flip, negative-positive transformation, and color component shuffling, after dividing the original imag...
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Context 1
... 255, 255}, as shown in Fig. 2. On the other hand, the proposed scheme prepares three random numbers of zero or one, which are generated by three keys K 4,R , K 4,G , and K 4,B . The negative-positive transformation of the three color components are operated independently according to the random numbers. In the case of the above example where {x R , x G , x B } = ...
Context 2
... 255, 255}, as shown in Fig. 2. On the other hand, the proposed scheme prepares three random numbers of zero or one, which are generated by three keys K 4,R , K 4,G , and K 4,B . The negative-positive transformation of the three color components are operated independently according to the random numbers. In the case of the above example where {x R , x G , x B } = ...
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This paper proposes a block-permutation-based encryption (BPBE) scheme for the encryption-then-compression (ETC) system that enhances the color scrambling. A BPBE image can be obtained through four processes, positional scrambling, block rotation/flip, negative-positive transformation, and color component shuffling, after dividing the original imag...
Citations
... The negative-positive transformation (NPT) is a commonly utilized encryption operation for securing images, particularly in compatible cryptosystems with compression techniques [1,2]. Notably, the NPT is employed in the encryption scheme of JPEG images, featuring prominently in various proposals [3][4][5][6][7]. In all of these instances, the NPT operates at the pixel block level [8] and applies to both color and grayscale images [9,10]. ...
... The correlation coefficient (ρ) assesses the confusion and diffusion effects in an encrypted image by considering pairs of pixels [34]. It is defined by Equation (4). In this context, let K represent the discrete random variable for the pixel color value in the original image, and Q denote the adjacent pixel color value in the original image. ...
The negative–positive transformation (NPT) is a widely employed technique for encrypting images on pixel blocks, commonly integrated into cryptosystems compatible with compression algorithms. The existing literature on NPT analysis can be categorized into two types: theoretical analyses with results that apply to any image, primarily focused on compression compatibility, and numerical analyses that report empirical results from specific images, some without explaining the causes of the security results, while others are only related to the compression performance. Consequently, there is a significant gap in understanding the implications of applying the NPT for data protection. For that reason, this paper conducts a theoretical statistical analysis, presenting, demonstrating, and verifying six theorems to understand the security contributions of NPT. Two theorems examine the shape of the image histogram and the scatter plot of adjacent pixels after the NPT application. The subsequent four theorems explore the influence of NPT on the mean, variance, covariance, and correlation within each pixel block. The findings indicate that the NPT generates images with symmetrical histograms, the correlation of pixel blocks remains invariant, and distinct vertical and horizontal reflections manifest on the scatter plot. These theorems are verified by encrypting the Lena image with four pixel-block sizes. The histogram symmetry passed the goodness-of-fit test at a significance level of 5%, revealing consistent results. The correlation of pixel blocks remained unchanged, and the scatter plot exhibited an x-shaped pattern. Therefore, as the NPT alone does not achieve desirable encryption results, such as uniform histograms, scatter plots, and decreasing correlation, cryptosystems should complement it with additional techniques.
... To endow ETCS with applicability for extensive scenarios, such as sharing images over an online social network (OSN) [26] and uploading images to a photo storage cloud [27], the embedded compression scheme should be a widely-used standard. To this end, a handful of block-wise perceptual encryption schemes compatible with JPEG compression standard or its variants were proposed in the past decade [28]- [34]. In JPEG, the lossy compression is performed for each block separately. ...
... For the former method, the correspondence is recovered by building a multi-branch tree, reducing the computational complexity remarkably. To make the cryptanalysis more complete, the security evaluation of the conventional ETCS proposed in [29]- [34] is also presented with reference to that of ETCS proposed in [35]. ...
... There are several conventional ETCSs proposed in [29]- [34], which are called as ETC in this paper for brevity. Some of them designed for JPEG-LS [33], [34] can be considered equivalent versions of ETCS that produces color cipherimages, so the previous analysis applies to them as well. ...
Joint encryption and compression is an ideal solution for protecting security and privacy of image data in a real scenario, e.g. storing them on an existing cloud-based service like Facebook. Recently, some block-wise encryption-then-compression (ETC) schemes compatible with JPEG were proposed to provide a reasonably high level of security without compromising compression ratio much. This paper investigates recovering the block-wise relationship in an ETC scheme exerting on single-color blocks of size $8\times 8$ in the scenarios of ciphertext-only attack, known-plaintext attack and chosen-plaintext attack. Then, the attacking targets are extended to the other conventional ETC schemes exerting on multiple color channels and blocks of various sizes. Especially, an elaborate jigsaw puzzle solver is designed to recover enough visual information from multiple cipher-images encrypted by the same secret key. Moreover, the nice attacking performance was verified over two social media platforms, Facebook and Weibo.
... To alter the color distribution in the Color CPE methods efficiently, Imaizumi et al. [31,47] proposed to process each color component individually in the permutation, rotation, inversion, and negative-positive transformation steps. This independent processing expands the keyspace size and modifies the color distribution significantly; however, this results in JPEG format compatibility issues. ...
... An extension of Color CPE method is proposed in [31,47] to better alter the color distribution. The principal idea is to process each color component independently. ...
Perceptual encryption (PE) hides the identifiable information of an image in such a way that its intrinsic characteristics remain intact. This recognizable perceptual quality can be used to enable computation in the encryption domain. A class of PE algorithms based on block-level processing has recently gained popularity for their ability to generate JPEG-compressible cipher images. A tradeoff in these methods, however, is between the security efficiency and compression savings due to the chosen block size. Several methods (such as the processing of each color component independently, image representation, and sub-block-level processing) have been proposed to effectively manage this tradeoff. The current study adapts these assorted practices into a uniform framework to provide a fair comparison of their results. Specifically, their compression quality is investigated under various design parameters, such as the choice of colorspace, image representation, chroma subsampling, quantization tables, and block size. Our analyses have shown that at best the PE methods introduce a decrease of 6% and 3% in the JPEG compression performance with and without chroma subsampling, respectively. Additionally, their encryption quality is quantified in terms of several statistical analyses. The simulation results show that block-based PE methods exhibit several favorable properties for the encryption-then-compression schemes. Nonetheless, to avoid any pitfalls, their principal design should be carefully considered in the context of the applications for which we outlined possible future research directions.
... The use of same key makes the systems vulnerable to jigsaw puzzle attack. The extended EtC method [16] proposed to process each color component independently by using different keys as K R i = K G i = K B i in steps i ∈ {1, 2, 3} for improved security. However, this results in a format compatibility issue, which has been addressed in [18]. ...
Perceptual encryption (PE) of images protects visual information while retaining the intrinsic properties necessary to enable computation in the encryption domain. Block–based PE produces JPEG-compliant images with almost the same compression savings as that of the plain images. The methods represent an input color image as a pseudo grayscale image to benefit from a smaller block size. However, such representation degrades image quality and compression savings, and removes color information, which limits their applications. To solve these limitations, we proposed inter and intra block processing for compressible PE methods (IIB–CPE). The method represents an input as a color image and performs block-level inter processing and sub-block-level intra processing on it. The intra block processing results in an inside–out geometric transformation that disrupts the symmetry of an entire block thus achieves visual encryption of local details while preserving the global contents of an image. The intra block-level processing allows the use of a smaller block size, which improves encryption efficiency without compromising compression performance. Our analyses showed that IIB–CPE offers 15% bitrate savings with better image quality than the existing PE methods. In addition, we extended the scope of applications of the proposed IIB–CPE to the privacy-preserving deep learning (PPDL) domain.
... An outline of the RDH-EtC method is shown in Figure 2. This method uses two of four processes in block-scrambling-based encryption for EtC systems [34,35]: position scrambling and block rotation or flip. Since an image histogram is not transformed before or after the encryption processes, we can embed a payload in plain and/or encrypted domains by using RDH-HS [3]. ...
... Most studies on EtC systems are based on the premise that a proprietary scheme is used for compression. Meanwhile, block-scrambling-based encryption methods [34,35], which are compatible with image coding standards, have been proposed for EtC systems. Chuman et al. [39] extended these methods to enhance security. ...
... Block-scrambling-based encryption is conducted on the grayscale image. Since the encrypted image is three times as large as the original image, the key space of the encrypted image is thereby larger than that of conventional methods [34,35]. This contributes to enhancing robustness against brute-force (BF) attacks. ...
This paper proposes a novel reversible data-hiding method in encrypted images to achieve both a high hiding capacity and good compression performance. The proposed method can also decrypt marked encrypted images without data extraction, so marked images containing a payload can be derived from marked encrypted images. A perceptual encryption algorithm proposed for an encryption-then-compression framework is used to generate compressible encrypted images. In addition, a predictor with high accuracy and a prediction-error expansion and histogram shifting method are used for data hiding. Consequently, the proposed method can compress marked encrypted images without loss using image coding standards and achieve a high hiding rate. Experimental results show the effectiveness of the method in terms of hiding capacity or marked-image quality and lossless compression efficiency.
... However, the use of the same key for each color component and larger block size result in a smaller number of blocks, which make the scheme vulnerable to jigsaw puzzle attack. To increase the number of blocks for better security, Imaizumi et al. [43] proposed to perform the first three steps of encryption independently in each color component. As a result, the scheme has a larger key space than that of [17]; however, processing each component individually results in the JPEG compatibility issues. ...
... For example, the method is only applicable with the JPEG lossless algorithm only when using RGB colorspace. Ahmad et al. [12,18] proposed a PE method to deal with the compatibility issue of [43]. In their proposed schemes, rotation, inversion and pixel values transformations are performed on each color component independently. ...
... The use of a same key for permutation step in each component allows the JPEG algorithm with YCbCr colorspace for better compression savings. The extended PE methods in [12,18,43] have better security than the PE method proposed in [17] as the keyspace is expanded and color distribution is altered significantly. However, the main limitation of extended PE methods is that they cannot exploit the JPEG chroma subsampling. ...
Block-based perceptual encryption (PE) algorithms are becoming popular for multimedia data protection because of their low computational demands and format-compliancy with the JPEG standard. In conventional methods, a colored image as an input is a prerequisite to enable smaller block size for better security. However, in domains such as medical image processing, unavailability of color images makes PE methods inadequate for their secure transmission and storage. Therefore, this study proposes a PE method that is applicable for both color and grayscale images. In the proposed method, efficiency is achieved by considering smaller block size in encryption steps that have negligible effect on the compressibility of an image. The analyses have shown that the proposed system offers better security with only 12% more bitrate requirement as opposed to 113% in conventional methods. As an application of the proposed method, we have considered a smart hospital that avails healthcare cloud services to outsource their deep learning (DL) computations and storage needs. The EfficientNetV2-based model is implemented for automatic tuberculosis (TB) diagnosis in chest X-ray images. In addition, we have proposed noise-based data augmentation method to address data deficiency in medical image analysis. As a result, the model accuracy was improved by 10%.
... On another front, several unique approaches have been developed to compress a marked encrypted image [15,16]. These methods use one type of encryption and then compression systems [19][20][21] that can efficiently compress an encrypted image using an image coding standard. ...
In this paper, we propose a novel reversible data hiding in encrypted images (RDH-EI) method that achieves the highest hiding capacity in the RDH-EI research field and full flexibility in the processing order without restrictions. In the previous work in this field, there exist two representative methods; one provides flexible processing with a high hiding capacity of 2.17 bpp, and the other achieves the highest hiding capacity of 2.46 bpp by using the BOWS-2 dataset. The latter method has critical restrictions on the processing order. We focus on the advantage of the former method and introduce two efficient algorithms for maximizing the hiding capacity. With these algorithms, the proposed method can predict each pixel value with higher accuracy and refine the embedding algorithm. Consequently, the hiding capacity is effectively enhanced to 2.50 bpp using the BOWS-2 dataset, and a series of processes can be freely conducted without considering any restrictions on the order between data hiding and encryption. In the same way, there are no restrictions on the processing order in the restoration process. Thus, the proposed method provides flexibility in the privileges requested by users. Experimental results show the effectiveness of the proposed method in terms of hiding capacity and marked-image quality.
... The first method to obtain effective compressibility for marked encrypted images is Imaizumi et al.'s method [21]. This method uses an encryption-then-compression (EtC) system [23,24] and thus can losslessly compress marked encrypted images using image coding standards, such as JPEG-LS [25] and JPEG 2000 [26]. Since an image histogram is not transformed before/after the encryption processes, flexible data hiding and extraction in plain and/or encrypted domains are accomplished by using an RDH method based on histogram shift (RDH-HS) [2]. ...
... This feature indicates that the RDH-EtC method can derive a marked image by decrypting without data extraction. The RDH-EtC method uses two of four processes in the block scrambling-based encryption for EtC systems [23,24]: position scrambling and block rotation/flip. Since these two scrambling processes do not transform image histograms, we can flexibly embed and extract a payload by using the RDH-HS method [2]. ...
... The RDH-EtC method [21] is used for region α. Here, the proposed method replaces the encryption process in [21] with Chuman et al.'s method [27], where the block scrambling-based encryption for EtC systems [23,24] is extended to enhance security. Note that the color conversion in [27] is not performed in our method to ensure full reversibility. ...
In this paper, we propose a new framework for reversible data hiding in encrypted images, where both the hiding capacity and lossless compression efficiency are flexibly controlled. There exist two main purposes; one is to provide highly efficient lossless compression under a required hiding capacity, while the other is to enable us to extract an embedded payload from a decrypted image. The proposed method can decrypt marked encrypted images without data extraction and derive marked images. An original image is arbitrarily divided into two regions. Two different methods for reversible data hiding in encrypted images (RDH-EI) are used in our method, and each one is used for either region. Consequently, one region can be decrypted without data extraction and also losslessly compressed using image coding standards even after the processing. The other region possesses a significantly high hiding rate, around 1 bpp. Experimental results show the effectiveness of the proposed method in terms of hiding capacity and lossless compression efficiency.
... This extension contributes to expanding the types of user authorities. We adopt the compressible encryption (CE) method [17][18][19][20] for high compression efficiency of the output image. Additionally, the RDH method based on histogram shift (HS) [2] is introduced in our method to embed a payload in both the plain and encrypted domains and flexibly extract the payload in either domain. ...
... Innovative frameworks for secure image transmission were proposed for encryption-then-compression (EtC) systems [13][14][15][16][17][18][19][20]. In the systems, encryption is performed by an image owner before compression/transmission. ...
... However, most of those methods do not support lossless compression of the encrypted images. The CE method has been developed for a solution to this issue [17][18][19][20]. The images encrypted by using this method are called EtC images. ...
We propose a reversible data hiding (RDH) method in compressible encrypted images called the encryption-then-compression (EtC) images. The proposed method allows us to not only embed a payload in encrypted images but also compress the encrypted images containing the payload. In addition, the proposed RDH method can be applied to both plain images and encrypted ones, and the payload can be extracted flexibly in the encrypted domain or from the decrypted images. Various RDH methods have been studied in the encrypted domain, but they are not considered to be two-domain data hiding, and the resultant images cannot be compressed by using image coding standards, such as JPEG-LS and JPEG 2000. In our experiment, the proposed method shows high performance in terms of lossless compression efficiency by using JPEG-LS and JPEG 2000, data hiding capacity, and marked image quality.
... Such encryption-then-compression framework does not seriously influence the further compression and can withstand the attacks based on conventional jigsaw puzzle solvers [109]. But, the correlation among blocks in cipher-images may still facilitate the advanced jigsaw puzzle solvers to optimize the attacking on the block-wise permutation schemes analyzed in [110,111]. ...
This paper aims to review the encountered technical contradictions when an attacker meets the cipher-images encrypted by the image encryption schemes (algorithms) proposed in 2018 from the viewpoint of an image cryptanalyst. The most representative works among them are selected and classified according to their essential structures. Almost all image cryptanalysis works published in 2018 are surveyed due to their small number. The challenging problems on design and analysis of image encryption schemes are summarized to receive the attentions of both designers and attackers (cryptanalysts) of image encryption schemes, which may promote solving scenario-oriented image security problems with new technologies.
