Secured signal modification and verification with privacy...

Details Secured signal modification and verification with privacy... Secured signal modification and verification with privacy...

1998-04-13

2001-07-03

Barroń, Jr., Gilberto (Department: 2131)

Electrical computers and digital processing systems: support

Multiple computer communication using cryptography

Particular communication authentication technique

C705S058000

Reexamination Certificate

active

06256736

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to imperceptible watermarking of human-perceptible data sets such as sound tracks, images, or videos, where such data sets have been digitized.
2. Background Description
An imperceptible watermark (hereafter watermark for short), is an alteration of the data set which is mostly not perceptible to a human, but can be recognized by a machine such as a computer. For instance, if the data set represents an image, the watermark should be (mostly) invisible; if the data set represents a sound track, the watermark should be (mostly) inaudible; and so on. The general principle of such watermarking has been disclosed in prior art.
Some watermarking schemes have been proposed to protect ownership, i.e., establish who is the rightful owner in situations when the ownership is contested. To the contrary we are interested here in watermarking techniques which are used to check the authenticity of a document by identifying the identity of the owner and/or the date of creation of a document. Alterations of the image should be detectable by an authentication algorithm, preferably in such a way that the location of the alterations can be located on the image. Authentication should still be possible on a portion of the image. Such watermarks are called fragile watermarks; they are modified (and the modification is detectable) by any modification of the image
See, for example, “An Invisible Watermarking Technique for Image Verification”, M. M. Yeung and F. C. Mintzer,
Proceedings
, International Conference on Image Processing 1997, vol. II pp. 680-683. This paper describes watermarking schemes where the owner of a data set incorporates an imperceptible watermark into the data set. As shown in prior art
FIG. 1
, the OWNER applies a watermarking scheme
102
to a source data set
101
to obtain the watermarked data set
103
. The watermarked data set is distributed to the CUSTOMER
104
. Both the OWNER and the CUSTOMER can authenticate
105
the data set by means of the
A related invention is “The Trustworthy Digital Camera: Restoring Credibility to the Photographic Image”, G. L. Friedman,
IEEE Trans. on Consumer Elec
., vol. 39, no. 4, 1993, pp. 905-910, and U.S. Pat. No. 5,499,294 by G. L. Friedman, which describes a digital camera which uses cryptography to create a signature for authenticating the images generated. A signature is created for the entire image and appended to the image.
This invention of G. L. Friedman is not a watermark since the signature is appended to the image instead of being embedded in it. This has several drawbacks:
1) To authenticate an image, one needs more than just the image; both the image and the signature are needed.
2) The locations where changes to the image are made cannot be determined.
3) A cropped version of the image cannot be authenticated as the signature depends on the full image.
4) The authentication algorithm needs access to the human-readable part of the image. Therefore the authentication agent, if different from the CUSTOMER, will also see the human-readable content of the image, a situation which can be undesirable. Drawbacks
1
through
3
are easily corrected by using a fragile watermark instead of appending the signature. However, in the present state of the art, this is at the cost of:
5) Altering the image more severely than just modifying the least significant bits.
6) A signature which does not offer the widely recognized advantages of Secret Key/Public Key (in short SK/PK) encryption. One of the advantages is the inability of the authenticating agent to watermark an image in the case when the authenticating agent is not the owner.
The present invention will correct all of these drawbacks.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a watermarking as faint, as secure, and as fast as possible with the possibility of tradeoffs between these requirements depending on the intended application.
It is also an object of the invention to provide watermarking using a SK/PK pair.
A further object of the invention is to embed a fragile watermark into an image such that the authentication agent does not need to know the human-readable content of the watermarked image in order to authenticate.
Another object of the invention is to provide the capability to authenticate a watermarked image without being able to watermark an image.
Still another object of the invention is to provide a watermarking scheme in which cropped images can be authenticated and detection of alteration can be localized, yet if pieces of the image are rearranged, the result ceases to be authentic.
Yet another object of the invention is to provide the capability to determine whether an image under consideration is cropped or not.
The present invention describes a data set distribution scheme where a possibly independent authentication agent can authenticate the data set without being able to read the human-readable data. Furthermore, optionally, the authentication agent A cannot watermark an image using the watermarking scheme of owner O. The general framework is presented in FIG.
2
. The owner of the source data
201
transforms it into a watermarked data set
206
by the following steps. First, privacy control
202
is added to the source data. This allows authentication while preserving the privacy of the content of the data set. Next a watermarking algorithm is applied
203
. This results in watermarked data which is privacy-enhanced
204
. Thanks to the fact that the watermark is image dependent, it may be affecting only the least significant bits of the image, which allows maximal image quality preservation. One cannot extract the human-readable content of the source data from the privacy enhanced watermarked data, but can still authenticate the data
212
. This watermarked privacy-enhanced data can be distributed from the owner to the authentication agent or to the customer. Furthermore, it can also be distributed between the authentication agent and the customer.
To recover the watermarked human-readable content, a privacy release algorithm is applied by the owner
205
or by the customer
209
. The resulting watermarked data
206
can be distributed from the owner to the customer
211
. The customer can then apply privacy control
210
to obtain the watermarked privacy-enhanced data
208
. The owner, the authentication agent and the customer in this scenario could be different parties or the same, depending on the application. This framework is thus much more general than the prior art described in FIG.
1
. The generality of this framework is further enhanced by the fact that some steps can be easily modified or omitted. For instance, all steps related to privacy protection may be avoided when there is no need for privacy: for instance an image distributor selling images to journals or individuals would not need these steps as opposed to a government agency keeping data on file which may need to have the authenticity of the files controlled while the content of the files remains secret.
As in the prior art (e.g. as disclosed by the Friedman paper), the present invention uses cryptography techniques for authentication. However, in Friedman's disclosure a signature is created for the entire image and the signature is appended to the image. In the present invention cryptography is used to create an embedded watermark which can be verified without needing to know the human readable content of the data set. This technique can also serve to prevent the authentication agent from watermarking an image.
The uses of the watermarking techniques of the present invention include authentication of data sets with encoding throughout the data set so that alterations can not only be detected, but also localized. Furthermore, given a cropped image, most of it can be authenticated. Also, the authentication algorithm can detect whether the image to be authenticated has been obtained by cropping a watermarked image.
Notice that the possibility of ve

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