Electrical computers and digital processing systems: support – Multiple computer communication using cryptography – Particular communication authentication technique
Reexamination Certificate
1999-09-17
2004-12-21
Sheikh, Ayaz (Department: 2767)
Electrical computers and digital processing systems: support
Multiple computer communication using cryptography
Particular communication authentication technique
C713S176000, C713S168000, C713S180000, C713S170000, C713S173000, C713S179000, C382S100000, C382S232000, C382S210000, C382S252000, C382S287000, C382S172000
Reexamination Certificate
active
06834344
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to digital watermarks and, more particularly, to semi-fragile digital watermarks which survive incidental modifications to an attached file caused by, for example, noise, compression-decompression, or digital to analog to digital (D/A/D) conversion of the file, which do not effect the authenticity of the file.
2. Description of the Related Art
The invention is directed to imperceptible watermarking of images. We define an imperceptible watermark (hereinafter simply “watermark”), as an alteration of the data set which is for the most part, imperceptible to a human (i.e., the watermark should be invisible or almost invisible), but can be recognized by a machine such as a computer. The general principle of such watermark has been disclosed, for instance in M. M. Yeung et al., “Digital Watermarking for High-Quality Imaging”, Proceedings of the IEEE Signal Processing Society Multimedia Workshop, Princeton, N.J., 1997.
Here we are interested in fragile watermarks, by which we mean watermarks which allow a system to recognize that an image is authentic and has not been altered, rather than in robust watermarks which are mainly devoted to establish ownership. As the invention relates to these two different types of technologies, we first review them at the level of detail and generality needed to describe the invention.
Fragile watermarks are designed to ensure that an image has not been modified. The principle is that if the image has been modified, the watermark alerts to this fact, and to some extent can localize where this modification has been done. Watermarks are usually based on some cryptographic techniques, and either secret or public keys can be used. In the current use of fragile watermarks, it is assumed that the image is always digital, by which we mean that it is kept and circulated as a file of numbers, and visualized and manipulated using a digital machine such as a computer. Fragile watermarks can be created and detected in several formats, compressed and/or uncompressed. As long as the image is kept in numerical form, data can be hidden in the file and retrieved by appropriate algorithms. The same image may be printed or reinterpreted with an analog machine, but it is not expected that the watermark be accessible after this transfer has been done.
It is often argued that fragile watermarks can be replaced by digital signatures, because all the scenario of creation and detection takes place at the digital level. However, a digital signature is an integer number that is obtained by a digital signature algorithm applied on a number associated in some prescribed way to the image, and is mainly used to authenticate the origin and integrity of the message or image whereas, digital watermarks are data hidden in, or more generally modifying, the pixels of the image file. On the other hand, watermarks can have many uses, including, but not limited to integrity verification. For example, robust watermarks are used for claiming ownership.
Robust watermarks are designed to survive modifications of the image, and more precisely, to remain detectable when the image has been modified to some reasonable extent. Robust watermarks are usually required to be non-removable by an adverse party. They can be designed to establish ownership, or to help protecting copyrights. In several cases, one expects them to still be detectable when the image is transferred to the analog world (prints or analog signals). The argument that watermarks can be replaced by signatures does not hold in this context, as known signature schemes do not resist transfer from the digital to analog world. Because of the dual constraint of invisibility and resistance, robust watermarks detection is based on statistical analysis. That is, any individual components of a mark can be altered by attack and/or by digital/analog (or D/A) conversion so that one is reduced to check that traces of the overall mark subsist. In general terms, one can say that a robust watermark consists in a mask M(K) defined by a cryptographically designed key K: the mask is used to modify some pixels attributes according to some algorithm, which defines the modification m(i, j) of the pixel (i, j)'s attributes as a function of the mask M, the pixel's attribute before marking A(i, j), and the attributes before marking Av(i, j) of neighboring pixels, i.e.,
m
(
i, j
)=
F
(
M
(
K
),
A
(
i, j
),
Av
(
i, j
))
Because the image and the accompanying watermark are expected to suffer some modifications, the key K is usually chosen as a secret key.
It would be quite advantageous to be able to reap the benefits of both fragile and robust invisible watermarks, and more precisely to have imperceptible watermarks for originality check which are fragile enough to detect significant modifications of the image, yet can still be detected to authenticate the image after minor modifications or modifications which may be significant but whose statistical properties are known or can be found through experimentation, such as printing and scanning, compression/decompression and/or high quality D/A/D conversion.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a semi-fragile watermark which is robust enough to provide an originality check but which is fragile enough to detect only significant modifications of the image.
It is yet another object of the present invention to provide a semi-fragile watermark which is substantially imperceptible by a human and can survive digital to analog and back to digital conversion.
It is yet a further object of the present invention to provide a semi-fragile watermark which can authenticate an image after modifications which may be significant but whose statistical properties are known or can be found through experiments, such as printing and scanning, compression/decompression and/or high quality D/A/D conversion.
According to the invention the benefits of robust watermarks (resistance to small modifications) with the benefits of fragile watermarks (detection of tampering of content) are combined.
Here we distinguish between minor modifications which are acceptable and/or unavoidable modifications to the image for which the modified image is still considered authentic and significant modifications which are modifications of the intended information content of the image. For instance, in the case when fragile watermarks are used to control that a picture of a car has not been modified, the intended information is the nature of the damages or the quality of the repairs. Suppose the modification due to, say, printing and scanning, changes the colormap of the image. We know statistically how the colormap would generally change, and so we do not use this component of image in producing the watermark. Thus the image after printing and scanning defines a number which, once coded, defines the same watermark.
A digital signature is a number that is obtained by encrypting a message or image through a digital signature algorithm and is mainly used to authenticate the integrity of the message or image. Digital watermarks are data added to the pixels of the image file. On the other hand, watermarks can have many uses, including, but not limited to integrity verification. For example, robust watermarks are used for claiming ownership. The present invention is to combine the benefits of robust watermarks (resistance to small modifications) with the benefits of fragile watermarks (detection of tampering of content).
One aspect of the present invention is that digital signature schemes do not have the same benefits as the proposed semi-fragile watermarking scheme since they cannot authenticate the image after lossy compression or printing and scanning. Also disclosed is how a visible signature, possibly computed using a public digital signature scheme such as Rivest-Shamir-Adleman (RSA), is attached to an image which can authenticate the image after minor and acceptable modifications. Anyone versed in
Aggarwal Gaurav
Dubey Pradeep K.
Kulshreshtha Ashutosh
Martens Marco
Tresser Charles P.
Coca T. Rao
International Business Machines - Corporation
Sheikh Ayaz
Whitham Curtis & Christofferson, P.C.
Zia Syed A.
LandOfFree
Semi-fragile watermarks does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Semi-fragile watermarks, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Semi-fragile watermarks will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3316742