Digital data watermarking system using novel watermark insertion and detection methods
View Patent ↗The watermarking system uses a first series of parameters, the private key, for the insertion of the watermark, and a second series of parameters, the public key, for the detection of the watermark, so that knowledge of the public key does not make it possible to know the private key and does not make it possible to delete or modify the watermark. The insertion of the watermark is performed by adding a pseudo random noise sequence, filtered by a filter with impulse response, to the data to be watermarked. The detection of the watermark is performed by searching through the data received for whether they contain noise which has been filtered by a filter with predefined spectral response. Application to copy protection.
1. A method for inserting a watermark into data (x) representing a content to be protected, comprising the steps of:
a) generating, from said data (x), a modulation sequence (m) representing the maximum amount of noise which can be added to said data,
b) supplying a pseudo random noise sequence (v) to the input of a filter with predefined impulse response (h);
c) multiplying said filtered pseudo noise sequence (w) with said modulation sequence; and
d) adding the filtered pseudo noise sequence (w) multiplied by the modulation sequence to said data.
2. The method according to claim 1 , further comprising the steps of:
e) performing a pseudo-random interleaving (p) of the modulation sequence (m) before step c)
f) performing the pseudo random interleaving (p) of the data (x) before step d); and
g) performing an inverse interleaving after step d) so as to obtain the watermarked data.
3. A method for detecting a watermark in data (r) representing a content received, comprising the steps of:
i) performing a spectral analysis of said data;
ii) estimating therefrom whether said data include a pseudo noise sequence which has been filtered by a filter with predefined spectral response (H(f)); and
iii) deducing from said estimation the presence of said watermark.
4. The method according to claim 3 for detecting a watermark in data (r) representing a content received, the watermark being adapted to be inserted in data (x) to be protected after performing a pseudo random interleaving (p) of said data to be protected, further comprising:
iv) performing, before step i), the pseudo random interleaving (p) of the data (r) received.
5. A device for inserting a watermark into data (x) representing a content to be protected, comprising:
means for generating a pseudo random noise sequence (v);
means for generating, from said data (x), a modulation sequence (m) indicative of the maximum amount of noise which can be added to said data;
filtering means having a predefined impulse response (h) and which are adapted for receiving said pseudo noise sequence (v) and for supplying a filtered pseudo noise sequence (w);
multiplication means for multiplying said filtered pseudo noise sequence (w) with said modulation sequence; and
means for adding the filtered pseudo noise sequence (w) multiplied by the modulation sequence (m) to said data (x).
6. The device according to claim 5 , further comprising:
first means of pseudo random interleaving of the data (x) representative of the content to be protected so as to supply interleaved data ({tilde over (x)}),
second means of pseudo random interleaving, adapted for performing the same interleaving as said first means of pseudo random interleaving, and adapted for receiving said modulation sequence (m) so as to supply an interleaved modulation sequence ({tilde over (m)}), said interleaved modulation sequence being supplied to the multiplication means for multiplication with said filtered pseudo noise sequence (w);
wherein the interleaved data are supplied to the addition means so as to be added to the filtered pseudo noise sequence (w) multiplied by the interleaved modulation sequence ({tilde over (m)}); and
means of inverse interleaving of said first interleaving means, linked to the output of said addition means so as to supply the watermarked data.
7. The device according to claim 6 , further comprising:
means for transforming the content to be protected into data (x) representative of said content;
means of inverse transformation of the watermarked data into a marked content.
8. A device for detecting a watermark in data (r) representing a content received, comprising:
means for obtaining the power spectral density of said data;
means of likelihood testing of hypotheses so as to estimate whether said data include a pseudo noise sequence which has been filtered by a filter with predefined spectral response (H(f)); and
means for deducing from said estimation the presence of said watermark.
9. The device according to claim 8 , adapted for detecting a watermark inserted by an insertion device, said insertion device comprising means of pseudo random interleaving of the data (x) to be protected so as to supply interleaved data ({tilde over (x)}) and means for inserting said watermark in said interleaved data ({tilde over (x)}) wherein the detection device furthermore comprises:
means of pseudo random interleaving of the data (r) representing the content received, which are adapted for performing the same interleaving (p) as said interleaving means of the insertion device, said interleaved data ({tilde over (r)}) being supplied to said means for obtaining the power spectral density.
10. The device according to claim 9 , adapted for detecting a watermark inserted by an insertion device further comprising means for transforming the content to be protected into data (x) representative of said content wherein said detection device furthermore comprises:
means for transforming the content received into data (r) representative of said content, said transforming means being adapted for performing the same transformation as the transforming means of the insertion device.