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Recently, a number of authentication schemes have been proposed for
multimedia data such as images and sound data. They include both label
based systems and semifragile watermarks. The main requirement for
such authentication systems is that minor modifications such as lossy
compression which do not alter the content of the data preserve the
authenticity of the data, whereas modifications which do modify the
content render the data not authentic. These schemes can be classified into two main classes depending on the model of image authentication they are based on. One of the purposes of this paper is to look at some of the advantages and disadvantages of these image authentication schemes and their relationship with fundamental limitations of the underlying model of image authentication. In particular, we study feature-based algorithms
which generate an authentication tag based on some inherent features
in the image such as the location of edges. The main disadvantage of
most proposed feature-based algorithms is that similar images generate
similar features, and therefore it is possible for a forger to
generate dissimilar images that have the same features. On the other
hand, the class of hash-based algorithms utilizes a cryptographic hash
function or a digital signature scheme to reduce the data and generate
an authentication tag. It inherits the security of digital signatures
to thwart forgery attacks. The main disadvantage of hash-based
algorithms is that the image needs to be modified in order to be made
authenticatable. The amount of modification is on the order of the
noise the image can tolerate before it is rendered inauthentic.
The other purpose of this paper is to propose a multimedia authentication scheme which combines some of the best features of both classes of algorithms. The proposed scheme utilizes cryptographic hash functions and digital signature schemes and the data does not need to be modified in order to be made authenticatable. We show how results in sphere packings and coverings can be useful in the design of the scheme. Several applications including the authentication of images on CD-ROM and handwritten documents will be discussed.
By: Chai Wah Wu
Published in: IEEE Transactions on Multimedia, volume 4, (no 3), pages 385-93 in 2002
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