13-11-2012, 02:26 PM
A Secret- Sharing-Based Method for Authentication of Grayscale Document Images via the Use of the PNG Image With a Data Repair Capability
ABSTRACT
A new blind authentication method based on the secret
sharing technique with a data repair capability for
grayscale document images via the use of the Portable
Network Graphics (PNG) image is proposed. An
authentication signal is generated for each block of a
grayscale document image, which, together with the
binarized block content, is transformed into several
shares using the Shamir secret sharing scheme. The
involved parameters are carefully chosen so that as many
shares as possible are generated and embedded into an
alpha channel plane. The alpha channel plane is then
combined with the original grayscale image to form a
PNG image. During the embedding process, the
computed share values are mapped into a range of alpha
channel values near their maximum value of 255 to yield
a transparent stego-image with a disguise effect. In the
process of image authentication, an image block is
marked as tampered if the authentication signal
computed from the current block content does not match
that extracted from the shares embedded in the alpha
channel plane. Data repairing is then applied to each
tampered block by a reverse Shamir scheme after
collecting two shares from unmarked blocks. Measures
for protecting the security of the data hidden in the alpha
channel are also proposed. Good experimental results
prove the effectiveness of the proposed method for real
applications.