19-07-2013, 02:09 PM
A Secret-Sharing-Based Method for Authentication of Grayscale Document Images via the Use of the PNG Image With a Data Repair Capability
A Secret-Sharing-Based Method.pdf (Size: 1.16 MB / Downloads: 70)
Abstract
A new blind authentication method based on the se-
cret 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.
INTRODUCTION
IGITAL image is a form for preserving important infor-
mation. However, with the fast advance of digital tech-
nologies, it is easy to make visually imperceptible modifications
to the contents of digital images. How to ensure the integrity and
the authenticity of a digital image is thus a challenge. It is de-
sirable to design effective methods to solve this kind of image
authentication problem [1]–[3], particularly for images of doc-
uments whose security must be protected. It is also hoped that,
IMAGE AUTHENTICATION AND DATA REPAIRING
In the proposed method, a PNG image is created from a bi-
nary-type grayscale document image with an alpha channel
plane. The original image may be thought as a grayscale
channel plane of the PNG image. An illustration of this process
of PNG image creation is shown in Fig. 2. Next, is bina-
rized by moment-preserving thresholding [13], yielding a bi-
nary version of , which we denote as . Data for authentica-
tion and repairing are then computed from and taken as input
to the Shamir secret sharing scheme to generate secret shares.
The share values are subsequently mapped into a small range
of alpha channel values near the maximum transparency value
to create an imperceptibility effect. Finally, the mapped secret
shares are randomly embedded into the alpha channel for the
purpose of promoting the security protection and data repair ca-
pabilities. Two block diagrams describing the proposed method
are shown in Figs. 3 and 4.
CONCLUSION
A new blind image authentication method with a data repair
capability for binary-like grayscale document images based on
secret sharing has been proposed. Both the generated authenti-
cation signal and the content of a block have been transformed
into partial shares by the Shamir method, which have been then
distributed in a well-designed manner into an alpha channel
plane to create a stego-image in the PNG format. The undesired
opaque effect visible in the stego-image coming from embed-
ding the partial shares has been eliminated by mapping the share
values into a small range of alpha channel values near their max-
imum transparency value of 255.