Cryptography – By modifying optical image
Reexamination Certificate
1999-06-08
2004-01-13
Barrón, Gilberto (Department: 2132)
Cryptography
By modifying optical image
C380S059000, C380S028000, C380S243000, C380S202000, C380S210000
Reexamination Certificate
active
06678378
ABSTRACT:
This patent application claims priority based on a Japanese patent application, H10-160603 filed on Jun. 9, 1998, the contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to encryption and decryption for 3-dimensional shape data, especially copyrighted data, representing a shape of a 3-dimensional object.
2. Description of the Related Art
The term “restoration” in this specification means an operation whereby data having been altered are restored closely to the original data. “Restoration” includes the case where restored data are not completely identical to the original data.
In the field of CAD (Computer Aided Design) and CG (Computer Graphics), 3-dimensional objects are drawn on 2-dimensional display screens using various methods. In CAD and CG, 3-dimensional shape data representing a shape of a 3-dimensional object are used. 3-dimensional shape data will become more and more important in a networked society where providers will distribute 3-dimensional shape data as digital content. 3-dimensional shape data will be needed for virtual digital 3D museums, 3D catalogs for cyber shopping and so on.
Transfer of 3-dimensional shape data can be carried out easily from one person to another via a portable recording medium such as an FD (Floppy Disc) or a CD (Compact Disc), or via a network such as the Internet.
Once 3-dimensional shape data have been transferred from a creator of the data, it is difficult to restrict how the data are used thereafter. In other words, a user who has received the 3-dimensional shape data can freely reproduce the 3-dimensional shape data without any permission of the original creator or copyright holder. In reality, even identifying such unauthorized use has been difficult.
SUMMARY OF THE INVENTION
An object of the present invention is therefore to provide 3-dimensional shape data encryption and decryption methods useful for preventing unauthorized use of a 3-dimensional object's shape represented by 3-dimensional shape data. Another object of the present invention is to provide 3-dimensional shape data encryption and decryption methods which enable identification of a user of 3-dimensional shape data.
According to a first aspect of the present invention, a 3-dimensional shape data encryption method comprising acquiring 3-dimensional shape data representing a shape of a 3-dimensional object, and generating encrypted data of the 3-dimensional object by altering the 3-dimensional shape data is provided.
The 3-dimensional object represented by the encrypted data differs from the 3-dimensional object represented by the 3-dimensional shape data before the alteration. Consequently, unless the encrypted data are restored as the original 3-dimensional shape data, the original 3-dimensional object will not be meaningfully displayed on a screen or the like. Therefore, management of a decryption key to restore the encrypted data leads to management of use permission/prohibition regarding the 3-dimensional shape data.
According to another aspect of the present invention, a 3-dimensional shape data decryption method comprising acquiring encrypted data of a 3-dimensional object, the encrypted data being generated by applying alteration to 3-dimensional shape data representing a shape of the 3-dimensional object, and generating decrypted data whereto an identifier has been added is provided.
Upon restoration of the encrypted data of a 3-dimensional object, decrypted data whereto an identifier has been added by altering the 3-dimensional shape data may be generated. This decryption method for 3-dimensional shape data is useful for adding an identifier (ID) to 3-dimensional shape data.
The identifier may be added to the decrypted data by maintaining at least a portion of the alteration included in the encrypted data. Alternatively, the identifier may be added to the decrypted data by a new alteration having no relation with the 3-dimensional shape data having been decrypted completely, or by an alteration thereto completely different from the alteration included in the encrypted data.
Thus, by distributing different copies to different users and recording the relation between the users and the copies it is possible to include the steps of detecting an illegal copy of the encrypted data and identifying a user for which a copy distributed to said user is the same as or close to the illegal copy.
In any case, by adding an alteration different for each decrypted data, the source of piracy can be identified by extracting the alteration related to ID. Especially, if an identifier is added by such alteration upon decryption, the shape distributor only has to generate a single common encrypted data.
It may be preferable for at least the alteration as an identifier to be imperceptible to humans when the 3-dimensional object is displayed on a display screen based on the decrypted data. This is because an identifier can be inserted without affecting display (image) quality of a 3-dimensional object.
Furthermore, upon decryption of the encrypted data of a 3-dimensional object generated by altering the 3-dimensional shape data, a restoration degree of the encrypted data may be specified so that the 3-dimensional shape data may be decrypted based on the specified restoration degree. If the restoration degree and the display quality of the decrypted 3-dimensional shape data are related to each other, an international variance in display quality of 3-dimensional object represented by the 3-dimensional shape data decrypted in accordance with the restoration degree may be generated.
According to a second aspect of the present invention, a 3-dimensional shape data encryption method comprising acquiring 3-dimensional shape data representing a shape of a 3-dimensional object, and generating encrypted data of the 3-dimensional object whereto an identifier has been added by altering the 3-dimensional shape data differently for each destination of the 3-dimensional shape data is provided.
In the above-described 3-dimensional shape data encryption and decryption methods, the 3-dimensional shape data may include topological data which may be specified by a structure graph of the 3-dimensional object. The structure graph may be generated based on a Reeb graph. The Reeb graph may be combined with Morse theory as known in the field of differential topology. According to Morse theory, a homotopy type space of a 3-dimensional object, that is, a structure of the 3-dimensional object can be reproduced by specifying singular points of a Morse function defined on a surface of the 3-dimensional object, and the kind (index) and order thereof. What is reproduced by Morse theory is merely a homotopy space. Therefore, by using a Reeb graph, the structure of the 3-dimensional object can be represented with more clarity. A Reeb graph is a structure graph or a skeleton graph as known in the field of topology.
The 3-dimensional shape data may include geometric data specifying the 3-dimensional coordinate values of the structure graph. Such geometric data may include coordinate values of each singular point included in the Reeb graph, an equation representing a curve connecting the singular points, and an equation representing a contour of a cross section of the 3-dimensional object. Only topological information is included in a Reeb graph, therefore, if geometric information is added to a Reeb graph, the shape of a 3-dimensional object can be specified more accurately.
REFERENCES:
patent: 4799103 (1989-01-01), Muckerheide
patent: 5374976 (1994-12-01), Spannenburg
Ryutarou Ohbuchi, “Watermarking Three-Dimentional Polygonal Models Though Geometric and Topological Modifications”, May 1998, IEEE journal, Vol 16.
Barrón Gilberto
Fleshner & Kim LLP
Gurshman Grigory
Monolith Co. Ltd.
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