今泉 祥子

In this paper, we propose a novel encryption method for JPEG bitstreams in which encrypted data can preserve the JPEG file format with the same size as that without encryption. Accordingly, data encrypted with the method can be decoded without any modification of header information by using a standard JPEG decoder. In addition, the method makes two contributions that conventional methods allowing bitstream-level encryption do not: spatially partial encryption and block-permutation-based encryption. To achieve this, we propose using a code called restart marker for the first time, which can be inserted at regular intervals between minimum coded units (MCUs) for encryption. This allows us to define extended blocks separated by restart markers, so the two contributions are possible with restart markers. In experiments, the effectiveness of the method is verified in terms of file size preservation and the visibility of encrypted images.

This paper proposes an extended method for reversible color tone control for blue and red tones. Our previous method has an issue in that there are cases where the intensity of enhancement cannot be flexibly controlled. In contrast, the proposed method can gradually improve the intensity by increasing the correction coefficients, regardless of the image features. This is because the method defines one reference area where the correction coefficients are determined, one each for blue and red tones, while the previous method defines a common reference area for both tones. Owing to this, the method also provides independent control for blue and red tones. In our experiments, we clarify the above advantages of the method. Additionally, we also discuss the influence of the data-embedding process, which is necessary to store recovery information, on the output image quality.

An RGB-D image has extra information, i.e.. depth information, which represents the distance between the camera and the objects. We extend a PEE-HS (prediction-error expansion with histogram shifting) based reversible data hiding method for RGB-D images to embed the depth information into the RGB layer without visible artifacts. The proposed method achieves the compatibility between the RGB-D and normal RGB images using a single marked image containing the depth information. Our experimental results show that the marked images have high quality without serious distortion.

This paper proposes a data hiding method for compressible encrypted images called the encryption-then-compression (EtC) images. We allocate bit planes of an original image to an encryption field and a data hiding field, where the upper 7 bits are encrypted by a compressible encryption (CE) method and LSBs are replaced with payload bits. By conducting the encryption and data hiding processes in the independent fields, the proposed method can embed and extract the payload flexibly without any complex condition and preprocessing. Experimental results and discussion show the effectiveness of the proposed method in terms of lossless compression efficiency by using JPEG-LS and JPEG 2000, marked-image quality, and robustness against attacks.

This paper proposes an extension of block-permutation-based encryption (BPBE) for the encryption-then-compression (ETC) system, which is more robust against some possible attacks compared to the conventional BPBE schemes. After dividing the original image into multiple blocks, the conventional schemes generate an encrypted image through four processes: positional scrambling, block rotation/inversion, negative-positive transformation, and color component shuffling. The proposed scheme achieves enhanced color scrambling by extending three of the four processes. The resilience against jigsaw puzzle solving problems can be consequently increased. The key space against brute-force attacks has also been expanded exponentially. Our scheme can maintain approximately the same compression efficiency compared with that of the conventional schemes.

In many multimedia applications, image encryption has to be conducted prior to image compression. This letter proposes an Encryption-then-Compression system using JPEG XR/JPEG-LS friendly perceptual encryption method, which enables to be conducted prior to the JPEG XR/JPEG-LS standard used as an international standard lossless compression method. The proposed encryption scheme can provides approximately the same compression performance as that of the lossless compression without any encryption. It is also shown that the proposed system consists of four block-based encryption steps, and provides a reasonably high level of security. Existing conventional encryption methods have not been designed for international lossless compression standards, but for the first time this letter focuses on applying the standards.

A robust scheme for identifying JPEG XR coded images is proposed in this paper. The aim is to identify the images that are generated from the same original image under various compression ratios. The proposed scheme is robust against a difference in compression ratios, and does not produce false negative matches in any compression ratio. A new property of the positive and negative signs of lapped biorthogonal transform coefficients is considered to robustly identify the images. The experimental results show the proposed scheme is effective for not only still images, but also video sequences in terms of the querying such as false positive, false negative and true positive matches.

In many multimedia applications, image encryption has to be conducted prior to image compression. This paper proposes a JPEG-friendly perceptual encryption method, which enables to be conducted prior to JPEG and Motion JPEG compressions. The proposed encryption scheme can provides approximately the same compression performance as that of JPEG compression without any encryption, where both gray scale images and color ones are considered. It is also shown that the proposed scheme consists of four block-based encryption steps, and provide a reasonably high level of security. Most of conventional perceptual encryption schemes have not been designed for international compression standards, but this paper focuses on applying the JPEG and Motion JPEG standards, as one of the most widely used image compression standards. In addition, this paper considers an efficient key management scheme, which enables an encryption with multiple keys to be easy to manage its keys.

We propose an efficient tamper detection scheme for JPEG2000 codestreams. The proposed scheme embeds information while maintaining the scalability function of JPEG2000 and can detect tampered layers or tampered resolution levels for each decoded image quality level. Marker codes that delimit a JPEG2000 codestream must not be generated in the body data that possesses the image information. We can prevent new marker codes from being generated when embedding information into the JPEG2000 codestream. The experimental results show that our scheme can preserve the high quality of the embedded images.

We propose a new approach that is an improvement on the conventional of a multi-bit information embedding algorithm for palette-based images. The proposed method embeds secret information by changing the pixel values for each of the 2(k-2) + 1 pixels. Hence, our scheme can embed more information compared to the conventional method. Furthermore, the developed algorithm does not drastically change the pixel values with large color differences between before and after the changes. Therefore, it reduces the degradation of the image quality. Our experimental results show that the proposed scheme is superior to the conventional method.

We propose a high-capacity data hiding scheme for palette-based images that does not seriously degrade the image quality in this paper. The proposed scheme can embed a multiple-bit message within the unit of a pixel matrix by using Euclidean distance, while some conventional schemes can embed only a one-bit message per pixel. The stego-images created by using our scheme offer a better quality compared to those by the conventional scheme. Moreover, we have obtained these results with low implementation cost. The experimental results show that the proposed scheme is efficient.

We present an efficient hierarchical scrambling scheme for palette-based images. The goal of hierarchical scrambling of a bit stream is to make the entire stream somehow difficult to decrypt. We decompose the original palette-based image into its corresponding binary bits then introduce cyclic shifts to scramble the selected entries and change their colors. The significant parameters (i.e. target pixels and target color components) play an important role in evaluating performance analysis. The scrambling scheme for the target pixels and the target color components were measured through a series of tests to measure the effectiveness of the proposed scheme. We also introduce an efficient key assignment scheme in which a recursive hash chain (RHC) is used to make our scheme secure.

We propose an efficient key assignment scheme for flexible access control of scalable media consisting of multidimensional scalability. The proposed scheme manages one key composed of a single key segment and assigns keys for each entity through hash chains. This scheme is also resilient to collusion attacks by which malicious users illegally access many more portions than they can legally. We introduce recursive hash chains to decrease the number of key segments to one, whereas the conventional schemes that have the above mentioned features must use multiple key segments to compose each key. The managed key is not delivered to any user for security against key leakage. Moreover, our scheme inhibits the amount of hash calculation. Performance analysis validates the proposed scheme. © 2013 IEEE.