今泉 祥子

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.

This paper proposes a hierarchical image authentication based on reversible data hiding. The proposed scheme decreases costs to detect and locate tampered area by using hierarchically multiplex layers. This scheme reduces both the length of embedded data and the amount of hash operations. We improve the structure of layers and the division of blocks in the conventional scheme. Our scheme is based on reversible watermarking. Evaluation of PSNR demonstrates the scheme we propose.

It is known that preference of some photographs is improved by adding noise. We propose "Memory texture" as a reason for the improvement of preference by the noise addition. "Memory texture" is the texture reproduced when we imagine the object. We investigated differences between real texture and memory texture by subjective evaluation of images added noise. Except as to potato image, memory textures were always not smaller than the real texture. Preferred textures were very close to the short-term memory texture in most objects.

We propose an efficient method of access control for hierarchical multimedia content. The proposed method simultaneously controls access to each medium contained in multimedia content and to each entity which is hierarchically organized in an individual medium. Even though this method achieves such fine control, it does not increase the computational complexity for key derivation. In our method, a service provider manages only a single key to control access to one multimedia content regardless of the number of media and the depth of hierarchy in each medium. The single managed key is not delivered to any user.

In this paper, an efficient data hiding scheme for printed color images is proposed that visualizes on printed color images embedded data that is invisible on a monitor. We accomplished this scheme by using the differences of color gamut between a monitor and printer. The proposed scheme visualizes embedded data by converting one piece of color information, either L*, a*, or b*, to a fixed value when printing. This feature can be easily applied to copyright protection for printed images. Simulation results show the effectiveness of our scheme.

We propose a key assignment scheme and applying it to control hierarchical access to multimedia content. By introducing a modified hash chain, the proposed scheme manages one key composed of a single segment. The managed key is not distributed to any users, providing security against key leakage. Collusion attacks are prevented by the order of key assignment. Our scheme also reduces the number of hash calculations. Analysis of performance demonstrated this scheme is valid. © 2012 IEEE.

An efficient key generating method that uses recursive hash chains is proposed for hierarchical access control. The proposed method introduces recursive hash chains for reducing the number of managed keys. In addition to decreasing this number down to one, regardless of the number of the controlled targets and their depth, the number of keys delivered to a user by using the proposed method is equal to or less than that in conventional methods.

This paper proposes a key derivation scheme to control access of JPEG 2000 (JP2) coded images, which consist of hierarchical scalability such as SNR, resolution levels, and so on. The proposed scheme simultaneously controls access to each level of scalability. The proposed scheme derives keys through hash chains, and each JP2 packet is enciphered with each individual key. By introducing combinations of a cyclic shift and a hash function, the proposed scheme manages only a single key for a JP2 image; whereas the conventional access control schemes having the above mentioned features manage multiple keys. The single managed key is not delivered to any user. The proposed scheme is also resilient to collusion attacks. Performance analysis shows the effectiveness of the proposed scheme.

We describe an efficient access control method for digital videos that controls access to video frames based on one-way hash functions. The method offers effective key management and delivery as well as conventional scalability-aware access control methods for coded still images. It uses hash chain-based key generation, thereby limiting the number of managed keys to one, and the user receives only one key as well. This method controls access to a video sequence based on frame rates, and it is applicable to access control of videos based on movie ratings. For access control with two controlled subjects, our method reduces the number of keys to the theoretical lower limit.

This paper proposes an access control method for composite multimedia content in which only a single key is delivered to a user. The proposed method simultaneously controls access to each medium in one composite multimedia content in which a medium can be hierarchically encoded. This method introduces recursive hash chains for key generation so that the number of delivered key is reduced to one, whereas the conventional method having the above mentioned features has to deliver multiple keys to a user. The managed key in the proposed method is also reduced to one.

This paper proposes an efficient access control method for content with multiple dimensions of hierarchical scalability. The proposed method versatilely serves various quality content by simultaneous control in every dimensions of scalability. This method manages single entity for the content and single encipher key, though it prevents users from colluding. A user receives single ciphered content and single decipher key to obtain the content with the permitted quality. In comparison to the conventional collusion attack-resistant access control methods, the sophisticated key generation manner in the proposed method reduces the required length of the managed key and that of the managed codestream.

This paper proposes an encryption method that uses short keys to enable hierarchical access controls for JPEG 2000 codestreams. The proposed method provides images of various quality levels that may be different from the quality at encoding, though it uses a single codestream and a single managed key (masterkey). Only one key generated from the masterkey is delivered to a user authorized to access a reserved quality image. This method also stems users' collusion to access superior-quality images. Some conventional methods of this proposed method serve the above features, but those keys are much longer than the proposed method. The proposed method uses the smaller number of partial keys than the conventional methods.

An encryption scheme is proposed that considers hierarchies in media, such as text, images, sound, and so on, in a composite multimedia content to enable versatile access control. In the proposed scheme, a content provider has only one managed key (the master key) for a particular composite multimedia content, and an user who is permitted to access a reserved content entities in the composite content receives only one key that is subordinately generated from the master key. Another key generated from the identical master key is delivered to another user, and this permits the user to access different entities. This scheme introduces a new key concept, namely "unusable key," to, keep all entities encrypted in a particular medium and to simultaneously decrypt several entities in other media. The other new key, "numbering key," is also used in this scheme to support simultaneous partial decryption of multiple images that are coded with a scalable coding technology. Simulation results show the effectiveness of the proposed scheme; in particular, the length of the managed master key and that of keys to be delivered to users are small.

This paper proposes a collusion attack-resilient method of encryption for access control of JPEG 2000 codestreams with hierarchical scalabilities. The proposed method generates one encryption key from one single key by multi-dimensional scanning to serve encryption keeping the scalability of codestrems. To avoid collusion attacks in which multiple users generate an illegal key from their own keys to overcome the access control, sufficient conditions are considered in this method. Moreover, a skip encryption is introduced to decrease the computational complexity and key management-and-delivery cost of encryption. Simulation results show the effectiveness of the proposed method.

This paper proposes an encryption scheme maintaining hierarchy of JPEG 2000 codestreams for flexible access control. JPEG 2000 generates hierarchical codestreams and has flexible scalability, such as, SNR, space, or color components. In a proposed method, only one managed key (master key) exists, and for a user permitted to access a reserved image quality, only one key generated by the master key is delivered. Also, a different key generated by the master key is delivered for a user permitted to access a different quality. The proposed access control method is available for all kinds of JPEG 2000 scalability. On the other hand, some conventional methods need several keys to control image quality. Another conventional method is not suitable for JPEG 2000 scalability.

本論文では,特殊命令コードであるマーカコードを発生せず,かつ新しい制御パラメータを有するJPEG2000符号化画像のための情報半開示方式を提案する.制御パラメータの導入は,半開示の画質,演算量及び不正解除に対する強度に関する制御能力を向上させる.演算量に関する制御能力の向上は,サイズの異なる画像に対して,半開示処理に要する処理負担をほぼ一定にすることを可能とする.この特長は,動画像のリアルタイム処理において重要な役割を果たす.

A method is described for efficient partial-scrambling of JPEG2000 images that avoids generating marker codes and improves the ability to control the degree, strength, and computational complexity of scrambling. This higher control ability is due to the use of a parameter. This parameter also controls the scrambling time, an important consideration for real-time processing.