Cryptography – Communication system using cryptography – Wireless communication
Reexamination Certificate
1998-10-14
2001-11-20
Hayes, Gail (Department: 2132)
Cryptography
Communication system using cryptography
Wireless communication
C380S036000, C380S037000, C380S054000, C380S205000, C375S130000, C713S176000, C713S179000
Reexamination Certificate
active
06320965
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to digital signal processing and, in particular, to a particularly robust watermark mechanism by which identifying data can be encoded into digital signals such as audio or video signals such that the identifying data are not perceptible to a human viewer of the substantive content of the digital signals yet are retrievable and are sufficiently robust to survive other digital signal processing.
BACKGROUND OF THE INVENTION
Video and audio data have traditionally been recorded and delivered as analog signals. However, digital signals are becoming the transmission medium of choice for video, audio, audiovisual, and multimedia information. Digital audio and video signals are currently delivered widely through digital satellites, digital cable, and computer networks such as local area networks and wide area networks, e.g., the Internet. In addition, digital audio and video signals are currently available in the form of digitally recorded material such as audio compact discs, digital audio tape (DAT), minidisc, and laserdisc and digital video disc (DVD) video media. As used herein, a digitized signal refers to a digital signal whose substantive content is generally analog in nature, i.e., can be represented by an analog signal. For example, digital video and digital audio signals are digitized signals since video images and audio content can be represented by analog signals.
The current tremendous growth of digitally stored and delivered audio and video is that digital copies which have exactly the same quality of the original digitized signal can easily be made and distributed without authorization notwithstanding illegality of such copying. The substantive content of digitized signals can have significant proprietary value which is susceptible to considerable diminution as a result of unauthorized duplication.
It is therefore desirable to include identifying data in digitized signals having valuable content such that duplication of the digitized signals also duplicates the identifying data and the source of such duplication can be identified. The identifying data should not result in humanly perceptible changes to the substantive content of the digitized signal when the substantive content is presented to a human viewer as audio and/or video. Since substantial value is in the substantive content itself and in its quality, any humanly perceptible degradation of the substantive content substantially diminishes the value of the digitized signal. Such imperceptible identifying data included in a digitized signal is generally known as a watermark.
Such watermarks should be robust in that signal processing of a digitized signal which affects the substantive content of the digitized signal to a limited, generally imperceptible degree should not affect the watermark so as to make the watermark unreadable. For example, simple conversion of the digital signal to an analog signal and conversion of the analog signal to a new digital signal should not erode the watermark substantially or, at least, should not render the watermark irretrievable. Conventional watermarks which hide identifying data in unused bits of a digitized signal can be defeated in such a digital-analog-digital conversion. In addition, simple inversion of each digitized amplitude, which results in a different digitized signal of equivalent substantive content when the content is audio, should not render the watermark unreadable. Similarly, addition or removal of a number of samples at the beginning of a digitized signal should not render a watermark unreadable. For example, prefixing a digitized audio signal with a one-tenth-second period of silence should not substantially affect ability to recognize and/or retrieve the watermark. Similarly, addition of an extra scanline or an extra pixel or two at the beginning of each scanline of a graphical image should not render any watermark of the graphical image unrecognizable and/or irretrievable.
Digitized signals are often compressed for various reasons, including delivery through a communications or storage medium of limited bandwidth and archival. Such compression can be lossy in that some of the signal of the substantive content is lost during such compression. In general, the object of such lossy compression is to limit loss of signal to levels which are not perceptible to a human viewer or listener of the substantive content when the compressed signal is subsequently reconstructed and played for the viewer or listener. A watermark should survive such lossy compression as well as other types of lossy signal processing and should remain readable within in the reconstructed digitized signal.
In addition to being robust, the watermark should be relatively difficult to detect without specific knowledge regarding the manner in which the watermark is added to the digitized signal. Consider, for example, an owner of a watermarked digitized signal, e.g., a watermarked digitized music signal on a compact disc. If the owner can detect the watermark, the owner may be able to fashion a filter which can remove the watermark or render the watermark unreadable without introducing any perceptible effects to the substantive content of the digitized signal. Accordingly, the value of the substantive content would be preserved and the owner could make unauthorized copies of the digitized signal in a manner in which the watermark cannot identify the owner as the source of the copies. Accordingly, watermarks should be secure and generally undetectable without special knowledge with respect to the specific encoding of such watermarks.
What is needed is a watermark system in which identifying data can be securely and robustly included in a digitized signal such that the source of such a digitized signal can be determined notwithstanding lossy and non-lossy signal processing of the digitized signal.
SUMMARY OF THE INVENTION
In accordance with the present invention, security of watermark data embedded in a watermarked signal is enhanced by obscuring the watermark data using an endless stream of pseudo-random bits. For example, the watermark data is obscured by encoding the data in a basis signal which is the result of spread-spectrum chipping in accordance with the stream of pseudo-random bits. As a result, successful decoding of the watermark data requires reproducing the spread-spectrum chipped basis signal in accordance with the stream of pseudo-random bits, therefore requiring reproduction of the stream of pseudo-random bits.
The stream of bits which are both reproducible and pseudo-random. The stream is endless in that the bit values are extremely unlikely to repeat until after an extremely long number of bits have been produced. For example, such an endless stream will generally produce repeating patterns of pseudo-random bits which are trillions of bits long. Recognizing such a repeating pattern is a practical impossibility. The length of the repeating pattern is effectively limited only by the finite number of states which can be represented within the pseudo-random generator producing the pseudo-random stream.
To produce an endless pseudo-random bit stream, subsequent bits of the sequence are generated in a pseudo-random manner from previous bits of the sequence. Pseudo-random bits are generated from data stored in a state in a pseudo-random, deterministic manner. The pseudo-random bits are appended to the stream of pseudo-random bits and, additionally, replace a number of bits of the state. The remaining bits are shifted such that, in effect, the least recently generated bits of the state are discarded. Thus, after production of a number of pseudo-random bits of the stream, the state changes significantly. Accordingly, repeating the above process generates additional pseudo-random bits which are very likely to differ significantly from the previously generated pseudo-random bits.
A basis signal is generated by spread-spectrum chipping in accordance with the stream of pseudo-random bits and watermark data is encoded in the basis signal to
Darrow Justin T.
Hayes Gail
Ivey James D.
Liquid Audio Inc.
LandOfFree
Secure watermark method and apparatus for digital signals does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Secure watermark method and apparatus for digital signals, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Secure watermark method and apparatus for digital signals will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2592308