Sunday, June 10, 2012

Robust digital signature for image authentication

The increasing amount of terror and treachery is posing a great threat to social security.
Terror mails having information modified and stuffed into images is increasing in use,
besides fraud information being transmitted by hackers cause a great deal of confusion
and distrust among parties.
In such cheating and fraudulent scenarios there is a dire need of an authentication
technique which can overcome all loopholes and provide a guaranteeing and trust worthy
information from a legitimate user.
This inspired us to take this project and play a part in providing solution to the current
Manipulations on images can be considered in two ways: method and purpose.
Manipulation methods include compression, format, transformation, shifting, scaling,
cropping, quantization, filtering, replacement, etc. The purpose of manipulations may be
transformation or attack. The former are usually acceptable, and the latter unacceptable.
We list two kinds of transformation
of representation below.
1) Format transformation and lossless compression. Disregarding the noise caused
by the precision limitation during computation, pixel values are not changed after
these manipulations. Therefore, we exclude these manipulations in the discussion
in this paper.
2) Application-specific transformations. Some applications may require the lossy
compression in order to satisfy the resource constraints on bandwidth or storage. Some
applications may also need to enhance the image quality, crop the image, change the size,
or perform some other operations. A common aspect of these manipulations is that they
change the pixel values, which results in different levels of visual distortion in the image.
Usually, most of these operations try to minimize the visual distortion. Attacks, or
malicious manipulations, change the image to a newone which carries a different visual
meaning to the observer. One typical example is replacing some parts of the image with
different content. It is difficult for an authenticator to know the purpose of manipulation.
A practical approach is to design an authenticator based on the manipulation method. In
this paper, we design an authenticator which accepts format
transformation, lossless compression, and the popular JPEG lossy compression. The
authenticator rejects replacement manipulations because they are frequently used for
attacks. Our authenticator does not aim to reject or accept, in absolute terms, other
manipulation methods because the problem of whether they are acceptable depends on
applications. But, if necessary, some manipulations can be clearly specified by users,
such as shifting, cropping, or constant intensity enhancement..

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