Electrical computers and digital processing systems: support – Multiple computer communication using cryptography – Particular communication authentication technique
Reexamination Certificate
1997-08-22
2001-09-04
Barron, Jr., Gilberto (Department: 2131)
Electrical computers and digital processing systems: support
Multiple computer communication using cryptography
Particular communication authentication technique
C380S054000, C382S248000
Reexamination Certificate
active
06286100
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to a data hiding method for hiding message data into media data and a data extracting method for extracting hidden data.
2. Prior Art
With the development of multimedia society, large quantities of digital video and audio information have been circulated on internet systems or as CD-ROM software. For digital video and audio information, any individual can easily create a perfect copy without degradation, so the illegal use and copyright protection are becoming problematic. In order to prevent a third party from illegally copying media data such as video and audio data, the technique of hiding additional information, such as the signature of an author, into original media data is becoming the focus of attention. When digital video data or other similar data is illegally copied, it could be known whether or not the copy is an illegal one by confirming the signature hidden in the copy and specifying the source. A hiding technique such as this is called data hiding.
As for the data hiding technique, a technique such as mentioned as follows is disclosed in “Nikkei Electronics 4-22 1996,” issued on Apr. 22, 1996.
FIG. 1
is a block diagram for explaining a conventional data hiding and extracting method. In the process of hiding an identification (ID) information, first, the frequency transform of media information, such as original dynamic images, still images, photographs, or audio, is performed by discrete cosine transform (DCT) or high-speed discrete Fourier transform (DFT) to obtain its frequency spectrum. Spectrum diffused and convoluted to this frequency spectrum of the media information is ID information. The ID information is a random specified to each purchaser of a work. The random-number generating algorithm employs a normal distribution, and the length is 1000. Then, the frequency spectrum of the media information to which the ID information was added is restored by inverse frequency transform to the original digital work having the hidden ID information. The digital work has the hidden ID information but is almost identical with the original work, so the purchaser cannot perceive the difference visually.
Conversely, in the process of extracting the ID information, first, the frequency transform of the digital work, thought of as an illegal copy, is performed to obtain its frequency spectrum and the frequency spectrum of the original work is also obtained. Then, the difference between these spectra is taken and compared with the ID information issued by the author. With this comparison, the purchaser of the work can be specified, so it can be judged whether or not the copy is illegal.
One of the features of the aforementioned technique is that frequency space is utilized for hiding data. That is, media information is transformed from real space to frequency space, and the frequency component in the frequency spectrum is operated based on ID information. Another feature is that a frequency region to be utilized is local. That is, the high-frequency component in the frequency spectrum of media information is not utilized and spectrum diffusion is performed only for a low-frequency region. The reason for this is that if ID information is diffused up to a high-frequency region, ID information is erased in compressing or decompressing the image. That is, this conventional technique spectrum-diffuses ID information locally in the frequency space of media information and hides the ID information in the entire real space of the media information.
The aforementioned conventional technique, however, has the disadvantage that message information (ID information) can be easily filtered out from media information by employing a frequency filter. For example, when media information with message information hidden therein is processed by employing a high-pass filter which filters out only a low-frequency component, the component of the high-frequency band remains unfiltered, but the component of the low-frequency band in which message information has been hidden is completely filtered out. Therefore, it is no longer possible to extract ID information from the media information that was output from a high-pass filter, and it is possible to hide different additional ID information.
SUMMARY OF THE INVENTION
Accordingly, it is the objective of the present invention to provide a data hiding method which has high resistance to removal or change of media information embedded into message information. Particularly, in the present invention it becomes possible to continue to effectively maintain hidden message information even when signal processing is performed by employing a frequency filter.
To solve the aforementioned problems, the present invention provides a data hiding method which embeds message information into media information. The data hiding method comprises the steps of:
(a) obtaining a frequency spectrum which contains a plurality of frequency components with respect to the message information;
(b) extracting a base region from the frequency spectrum of the message information, the base region being defined as a region which contains feature frequency components that represent features of the message information in real space;
(c) generating a plurality of copies of the base region and generating a frequency spectrum obtained by dispersedly arranging the respective copies in frequency space, as intermediate information; and
(d) hiding the message information into the media information by operating the frequency spectrum of the message information, based on the intermediate information.
Also, the present invention provides a data hiding method which hides message information into media information. The data hiding method comprises the steps of:
(a) obtaining a frequency spectrum which contains a plurality of frequency components with respect to the message information;
(b) extracting a base region from the frequency spectrum of the message information, the base region being defined as a region which contains feature frequency components that represent features of the message information in real space;
(c) generating a plurality of copies of the base region and generating a frequency spectrum obtained by dispersedly arranging the respective copies in frequency space, as intermediate information; and
(d) hiding the message information into the media information by executing an arithmetic based on both the intermediate information and the media information.
Here, it is preferable that the base region contain a plurality of frequency components which represent external features of the message information in real space. Particularly when the media information is image information, it is preferable that the base regions be constituted by a plurality of low-frequency components which represent contour features of an image in real space.
Also, in the step (b), a plurality of base regions may be extracted. In this case, for each of the base regions.
The aforementioned copies each may have the same frequency component as the feature frequency component of the base region. Also, it is preferable that among the frequency components of the frequency spectrum as the intermediate information, frequency components other than positions at which the copies are arranged are zero.
Furthermore, it is preferable that the arithmetic in the step (d) be a binomial arithmetic more specifically addition. Note that a step of performing inverse frequency transform of a result obtained in the step (d) is executed when the arithmetic in the step (d) is executed in frequency space.
Still further, the present invention relates to a data extraction method which extracts message information from media information with the message information hidden multiply in frequency space. The data extraction method comprises the steps of:
(a) obtaining, as first intermediate information, a frequency spectrum which has a plurality of base regions by operating the media information with the message information hidden therein, each of the base regions
Morimoto Norishige
Ninomiya Syoiti
Tezuka Shu
Barron Jr. Gilberto
International Business Machines - Corporation
Latham Bryan
Scully Scott Murphy & Presser
Underweiser Marian
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