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Taichi Isogai

Bio: Taichi Isogai is an academic researcher from Toshiba. The author has contributed to research in topics: Finite field & Watermark. The author has an hindex of 6, co-authored 30 publications receiving 149 citations.

Papers
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Patent
20 Sep 2005
TL;DR: A digital watermark detecting apparatus includes an acquisition unit configured to acquire a plurality of base values for computation of a watermark value, which are contained, respectively, in all or some of the divided regions obtained by dividing digital contents.
Abstract: A digital watermark detecting apparatus includes an acquisition unit configured to acquire a plurality of base values for computation of a watermark value, which are contained, respectively, in all or some of a plurality of divided regions obtained by dividing digital contents, a computation unit configured to compute variance of the base values, and a determination unit configured to determine whether the digital watermark is contained in the digital contents, based on comparison of the computed variance with a threshold.

27 citations

Patent
Taichi Isogai1
01 Sep 2006
TL;DR: In this paper, a digital watermark embedding system includes a watermark providing unit, an obtaining unit, and an overlapping unit to overlap the first image pattern and the second image pattern to eliminate or reduce the image component.
Abstract: A digital watermark embedding apparatus includes a watermark providing unit configured to provide a digital watermark, an obtaining unit configured to obtain an image component from a plurality of frames of video contents based on image data of the plurality of frames, the image component affecting an error occurring at a time of detecting an image pattern of the digital watermark, a generating unit configured to generate a first image pattern and a second image pattern in converse relation, using the image pattern of the digital watermark and the image component, and an overlapping unit configured to overlap the first image pattern and the second image pattern the frames on the frames, respectively, to eliminate or reduce the image component.

18 citations

Patent
Taichi Isogai1
24 Sep 2004
TL;DR: An apparatus for embedding digital watermark information in an image, includes an image divider dividing the image into a plurality of partial images; and an embedder embedding in each of the partial images a watermark which indicates the digital watermarks information as discussed by the authors.
Abstract: An apparatus for embedding digital watermark information in an image, includes an image divider dividing the image into a plurality of partial images; and an embedder embedding in each of the partial images a digital watermark which indicates the digital watermark information. The digital watermark includes a plurality of watermark elements arranged in a sequence which is different for each of the partial images.

13 citations

Patent
Taichi Isogai1
18 Aug 2006
TL;DR: In this paper, the authors proposed a digital watermark detection apparatus that includes a watermark component extracting unit which extracts each watermark components from the motion image; an average value computing unit which computes an average values of component values of pixels included in the watermark, and an identified water-mark component determination unit which determines whether or not the water-marks component is an identified Watermark component, to be utilized in identifying an arrangement unit of a plurality of watermarks.
Abstract: A digital watermark detection apparatus detects a watermark value from a motion image in which a topological invariant is embedded as the watermark value. The digital watermark detection apparatus includes a watermark component extracting unit which extracts each watermark component from the motion image; an average value computing unit which computes an average value of component values of pixels included in the watermark component; an identified watermark component determination unit which determines whether or not the watermark component is an identified watermark component to be utilized in identifying an arrangement unit of a plurality of watermark components based on the average value; a watermark component identifying unit which identifies the watermark component except for the identified watermark component; and a watermark value computing unit which computes the watermark value based on the identified watermark component and the watermark components except for the identified watermark component.

10 citations

Patent
19 Mar 2009
TL;DR: In this article, a parameter generating device includes an input receiving unit that receives a degree n of an algebraic torus T and an output unit that outputs parameters when it is determined that the cryptosystem is secure.
Abstract: A parameter generating device includes an input receiving unit that receives a degree n of an algebraic torus T including a group G in which a cryptosystem used in a torus-compressed public key cryptosystem is defined, a size W of a finite field F, and a size S of the group G, an extension-degree determining unit that determines an extension degree m of a finite field Fpm in which the algebraic torus T is defined, a first prime-number search unit that searches for a prime number p, a second prime-number search unit that searches for a prime number q, a test unit that checks whether a multiplication value nm is divisible by the prime number q, a security determining unit that determines that the cryptosystem is secure based on the multiplication value nm, and an output unit that outputs parameters when it is determined that the cryptosystem is secure.

8 citations


Cited by
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Patent
TL;DR: In this paper, a system for using a watermark embedded in an audio signal to remotely control a device is described. But the watermarks can be used with a "time gate" device, where detection of the watermark opens a time interval within which a user is allowed to perform an action, such as pressing a button, typing in an answer, turning a key in a lock, etc.
Abstract: A system for using a watermark embedded in an audio signal to remotely control a device. Various devices such as toys, computers, and appliances, equipped with an appropriate detector, detect the hidden signals, which can trigger an action, or change a state of the device. The watermarks can be used with a “time gate” device, where detection of the watermark opens a time interval within which a user is allowed to perform an action, such as pressing a button, typing in an answer, turning a key in a lock, etc.

186 citations

Patent
01 Jul 2005
TL;DR: In this article, the auxiliary information in a host content signal has been used to reduce the memory, bandwidth and computational complexity of the embedding and transmission systems, thus reducing the storage and transmission requirements of the watermarking system.
Abstract: Methods are provided for embedding auxiliary information in a host content signal which reduce the memory, bandwidth and computational complexity of the embedding and transmission systems. In one embodiment, a first reduced-scale signal is produced which corresponds to the host content embedded with a first logical value and producing a second reduced-scale signal corresponding to the host content embedded with a second logical value. A first set of segments from the first reduced-scale signal may be combined with a second set of segments from the second reduced-scale signal in a pre-defined manner to produce a composite embedded host content. Thus the storage and transmission requirements of the watermarking system are reduced to having to deal with only the original content plus two reduced-scale signals.

142 citations

Patent
19 Jun 2007
TL;DR: In this paper, video fingerprints provide a compact representation of the temporal locations of discontinuities in the video that can be used to quickly and efficiently identify video content, such as shot boundaries in video frame sequence or silent points in audio stream.
Abstract: A method and system generates and compares fingerprints for videos in a video library. The video fingerprints provide a compact representation of the temporal locations of discontinuities in the video that can be used to quickly and efficiently identify video content. Discontinuities can be, for example, shot boundaries in the video frame sequence or silent points in the audio stream. Because the fingerprints are based on structural discontinuity characteristics rather than exact bit sequences, visual content of videos can be effectively compared even when there are small differences between the videos in compression factors, source resolutions, start and stop times, frame rates, and so on. Comparison of video fingerprints can be used, for example, to search for and remove copyright protected videos from a video library. Furthermore, duplicate videos can be detected and discarded in order to preserve storage space.

86 citations

Patent
07 Jul 2006
TL;DR: In this article, the authors proposed a scheme to embed auxiliary information in encrypted host signals using digital watermarks, without the knowledge of the encryption/decryption keys, and the embedded watermarks persist throughout the content subsequent to decryption of the content.
Abstract: Methods, apparatus and systems for embedding auxiliary information in encrypted host signals are provided. The present invention enables secure application of digital watermarks at any point in the transmission and/or distribution of digital content by enabling the insertion of a plurality of digital watermarks, without the knowledge of the encryption/decryption keys, into a digital host content that has been encrypted with an encryption key. The embedded watermarks persist throughout the content subsequent to the decryption of the content. The disclosed techniques are applicable to content that has been encrypted using a variety of different encryption techniques and algorithms, including stream ciphers, block ciphers, symmetric and asymmetric encryption algorithms. These methods are further adapted to enable the insertion of watermarks into a content that is compressed prior to encryption.

85 citations

Journal Article
TL;DR: This approach is an alternative to a recent paper of Granger and Vercauteren for computing discrete logarithms in tori, using efficient torus representations, and shows that when q is not too large, a very efficient L(1/3) variation of the function field sieve can be used.
Abstract: In this paper, we study the application of the function field sieve algorithm for computing discrete logarithms over finite fields of the form F q n when q is a medium-sized prime power. This approach is an alternative to a recent paper of Granger and Vercauteren for computing discrete logarithms in tori, using efficient torus representations. We show that when q is not too large, a very efficient L(1/3) variation of the function field sieve can be used. Surprisingly, using this algorithm, discrete logarithms computations over some of these fields are even easier than computations in the prime field and characteristic two field cases. We also show that this new algorithm has security implications on some existing cryptosystems, such as torus based cryptography in T 30 , short signature schemes in characteristic 3 and cryptosystems based on super-singular abelian varieties. On the other hand, cryptosystems involving larger basefields and smaller extension degrees, typically of degree at most 6, such as LUC, XTR or T 6 torus cryptography, are not affected.

81 citations