Cryptography – Video cryptography – Copy protection or prevention
Reexamination Certificate
1999-06-21
2004-05-04
Barrón, Gilberto (Department: 2132)
Cryptography
Video cryptography
Copy protection or prevention
C380S202000, C713S189000
Reexamination Certificate
active
06731756
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention (Technical Field)
The present invention relates to the field of displaying digital images on a computer, and in particular to the protection of these images from unauthorized copying.
2. Background Art
One of the fundamental problems associated with making multimedia content (e.g., digital images, digital video, and digital audio) publicly available over the global internet is the inability of stopping anyone who accesses the content from copying it, and subsequently distributing it to others. For example, using the Microsoft Internet Explorer® or the Netscape Navigator® browsers, a user can press the right mouse button while a multimedia object in the browser is selected, and they are then given the option of saving this object. Furthermore, in the case of digital images, the Microsoft Windows® 95, 98, or NT operating systems generally allow a user to perform a “screen capture”, saving a copy of whatever is displayed on the screen. In these operating systems, this is accomplished by pressing the “Print Screen” button on the computer keyboard, thereby saving a bit-mapped image of the computer screen in a “clipboard”. The clipboard can then be “pasted” into image processing applications that can manipulate the bit-mapped image, allowing one to save selected regions of the bit-map. In addition, there are a number of software applications that provide more sophisticated image capture capabilities, including “HyperSnap-Dx”, G. Koshaniak, and “Capture Professional”. Recently, a number of products related to the idea of a “secure container” have been proposed, including DigiBox™ by InterTrust Technologies Corporation, “The DigiBox: A Self-Protecting Container for Electronic Commerce”, O. Sibert, Dbernstein, and D. Van Wie,
USENIX
1995
Electronic Commerce Workshop
, and Cryptolopes® by the IBM Corporation, “Cryptolope Containers”. The generic idea involves encapsulating encrypted digital content, along with a set of rules for decrypting the content, within the secure container. Users are only allowed to decrypt specific pieces of the content, as specified by the rules, once they have obtained authority for doing so. Typically, access to the encrypted content is controlled via a “key exchange” over a separate channel to each user (e.g., Cryptolope® uses RSA public key encryption). If the proper authority is granted to a user, then that user is able to use their specific key to “unlock” portions of the content, thereby obtaining a “clear view” of the content. This same concept can be extended to groups of users.
With respect to images, secure containers prevent a protected image from being viewed until a user is given the proper authority. Once the image is viewable; however, secure containers do not specifically prevent the image from being copied using screen capture programs. To address this problem, a number of “countermeasures” have been employed by content providers in order to discourage illicit copying of images once they are in “clear view”. These include placing visible watermarks in an image, or only making a “low resolution” version of the image available for viewing. However, each of these approaches is lacking in one way or another. For example, visible watermarks are in general easily removed using simple image processing operations, and in both of the cases cited above, the prospective buyer does not get to view the image they may wish to buy. Ideally, a consumer should be able to view the actual content they are contemplating purchasing, but they should not be able to download this content unless the owner of the content has granted permission to do so.
An example of the present methodology for securing video images is in U.S. Pat. No. 5,881,287 to Mast, entitled Method and Apparatus for Copy Protection of Images in a Computer System. However, as can be seen, there are several deficiencies in the Mast patent. The embodiment in Mast discloses a library, plus a set of installed services to be used by other applications. The present invention is an application. The copy protection is provided to the image files, not as a run-time service to other applications. Additionally, The present invention does not require the presence or installation of services or other applications other than provided by the operating system-level components.
In the Mast patent, the sole mode of copy protection once the image has been decrypted, requires the use of windows hooks as means to protect the images in disk and video memory. The present invention does not rely or require any kind of hook mechanism. Hook global mechanisms are not favored in environments where process security is important. The present invention uses direct manipulation of video memory that will bypass hook mechanisms. Mast requires that the applications that use the protection provided by said invention, be modified to link and make calls into the protection DLL (BITBLOCK.DLL). In addition, the protection DLL must make calls to the protected applications. The present invention does not require other programs to be modified to accommodate the means of protection. In addition, the present invention does not rely on calls to other applications to provide the means of protection. The means of protection relies solely on calls to operating system-level services.
Mast also requires the protection DLL (BITBLOCK.DLL) to install a callback function into the Microsoft Windows 3.1® BitBlt( ) GDI function hook chain. The present invention does not make use of protection DLLs, nor does it use callback functions to provide means of protection. The Mast invention requires a device driver and a means for intercepting memory read requests. The present invention does not rely or require device drivers or other standalone decryption services, although it can be implemented using them. Decryption is provided as a routine embedded in the application.
The general goal of the present invention is to allow multimedia content providers to make their intellectual property (i.e., their images) publicly available, while at the same time preventing those who view these images from copying them. Specifically, during the time an image is viewable, the present invention prevents the image from being copied or screen captured. Thus, if users attempt to view the image from “outside” the secure viewer, they will only see the noise-like encrypted content. Under specific conditions, the secure viewer will allow a user to copy an image, but only if the user possesses a secret key necessary to decrypt the image. This gives content owners the ability to control who is able to save their images. Note that this approach is quite different from the manner in which secure containers are used. In particular, under a specific viewing mode (and assuming the image is encrypted for this mode) a user can always view the image; however, they are never able to copy it. This security is accomplished in the secure viewer by directly controlling the client system output devices. Specifically, the present invention details how operating system services or custom device drivers can be used to gain direct control of video hardware. In its present embodiment in the Microsoft Windows® 95/98/NT platforms, it uses the services of DirectX® to directly manipulate and control the video hardware. Other embodiments are possible, as described below.
SUMMARY OF THE INVENTION (DISCLOSURE OF THE INVENTION)
In accordance with the present invention, there is provided a method of securing video images in computer systems. The invention provides a method of allowing copies of images to be made only with authorization. The preferred method of preventing illicit copying of a displayed image from a computer video memory comprises the steps of decoding a proprietary image format into video memory, controlling video hardware and locking video memory and displaying the image. The preferred step of decoding a proprietary image format into video memory comprises decrypting a previously encrypted image using a secret key. The preferred step of co
Heileman Gregory L.
Pizano Carlos E.
Armijo Dennis F.
Barrón Gilberto
Elisar Software Corporation, Inc.
Gurshman Grigory
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