Methods and apparatus for thwarting watermark detection circumvention
Methods and apparatus for thwarting circumvention of watermark detection are provided. When content is received at a device that is equipped with a watermark extractor, an attacker may disguise the form of the received content in an attempt to circumvent detection of watermarks that are embedded in the content. A signal processing operation is performed on the received content such that the signal processing operation does not significantly degrade the perceptual quality of the content if the content is indeed in the form that is purported to be. The signal processing operation, however, significantly degrades the perceptual quality of the content if the content is in a different form, thereby discouraging the attacker's attempts to thwart watermark detection.
1. A method for thwarting circumvention of watermark detection, comprising:
receiving a content at a content handling device that is equipped with a watermark extractor, the content comprising one or more embedded watermarks, the watermarks having been embedded in a first form of the content; and
performing a signal processing operation on the received content, wherein the signal processing operation does not substantially degrade perceptual quality of the received content if the received content is in the first form, and wherein the signal processing operation substantially degrades perceptual quality of the received content if, in an attempt to circumvent detection of one or more of the embedded watermarks, the received content has been modified to be in a second form.
2. The method of claim 1 , wherein the content in the second form is produced by carrying out a transformation operation on the content in the first form.
3. The method of claim 2 , wherein the transformation operation is a lossless transformation operation.
4. The method of claim 1 , wherein the content in the second form corresponds to one of:
a scrambled content;
an encrypted content; and
a modulated content.
5. The method of claim 1 , wherein
the content in the first form is an audio-visual content; and
the content in the second form is not recognized as an audio visual content by a watermark detection device.
6. The method of claim 1 , further comprising analyzing the received content to ascertain presence of a particular characteristic in the received content, wherein the signal processing operation is performed if the particular characteristic is present.
7. The method of claim 6 , wherein the particular characteristic corresponds to one of:
a statistical feature indicative of a flat frequency spectrum;
a statistical feature that does not follow statistical norms associated with typical multimedia content;
a specifically designed reference signal; and
a characteristic inconsistent with typical multimedia content.
8. The method of claim 1 , wherein the signal processing operation comprises at least one of:
an analog-to-digital (A/D) operation;
a digital-to-analog (D/A) operation;
a lowpass filtering operation;
a bandpass filtering operation;
a resampling operation;
a non-linear distortion operation; and
an allpass filtering operation.
9. The method of claim 1 , wherein the signal processing operation is carried out on only a portion of the received content.
10. The method of claim 1 , wherein the signal processing operation is adapted to degrade the perceptual quality of the content in the second form with different levels of variability.
11. The method of claim 1 , further comprising conducting a watermark extraction operation, wherein the signal processing operation is performed only if no embedded watermarks are extracted.
12. The method of claim 11 , wherein the extraction operation comprises converting at least a portion of the received content into a different domain and conducting the watermark extraction operation in the different domain.
13. The method of claim 12 , wherein the converting comprises inverting one or more content sample values in at least one of a temporal, spatial and frequency domains.
14. The method of claim 1 , wherein the signal processing operation is performed on a signal that is input to the watermark extractor.
15. A device, comprising:
a receiver configured to receive a content at a content handling device that is equipped with a watermark extractor, the content comprising one or more embedded watermarks, the watermarks having been embedded in a first form of the content;
a processor configured to perform a signal processing operation on the received content, wherein the signal processing operation does not substantially degrade perceptual quality of the received content if the received content is in the first form, and wherein the signal processing operation substantially degrades perceptual quality of the received content if, in an attempt to circumvent detection of one or more of the embedded watermarks, the received content has been modified to be in a second form.
16. The device of claim 15 , wherein the content in the second form is produced by carrying out a transformation operation on the content in the first form.
17. The device of claim 16 , wherein the transformation operation is a lossless transformation operation.
18. The device of claim 15 , wherein the content in the second form corresponds to one of:
a scrambled content;
an encrypted content; and
a modulated content.
19. The device of claim 16 , wherein
the content in the first form is an audio-visual content; and
the content in the second form is not recognized as an audio visual content by a watermark detection device.
20. The device of claim 15 , wherein the processor is further configured to analyze the received content to ascertain presence of a particular characteristic in the content and to perform the signal processing operation if the particular characteristic is present.
21. The device of claim 20 , wherein the particular characteristic corresponds to one of:
a statistical feature indicative of a flat frequency spectrum;
a statistical feature that does not follow statistical norms associated with typical multimedia content;
a specifically designed reference signal; and
a characteristic inconsistent with typical multimedia content.
22. The device of claim 15 , wherein the signal processing operation comprises at least one of:
an analog-to-digital (A/D) operation;
a digital-to-analog (D/A) operation;
a lowpass filtering operation;
a bandpass filtering operation;
a resampling operation;
a non-linear distortion operation; and
an allpass filtering operation.
23. The device of claim 15 , wherein the processor is configured to carry out the signal processing operation on only a portion of the received content.
24. The method of claim 15 , wherein the signal processing operation is adapted to degrade the perceptual quality of the content in the second form with different levels of variability.
25. The device of claim 15 , further wherein the processor is further configured to conduct a watermark extraction operation and to perform the signal processing operation only if no embedded watermarks are extracted.
26. The device of claim 25 , wherein the watermark extraction operation comprises converting at least a portion of the received content into a different domain and conducting the watermark extraction operation in the different domain.
27. The device of claim 26 , wherein the converting comprises inverting one or more content sample values in at least one of a temporal, spatial and frequency domains.
28. The apparatus of claim 15 , wherein the processor is configured to perform the signal processing operation on a signal that is input to the watermark extractor.