Cryptography Reference
In-Depth Information
is that replacing a noise-like portion with any noise-like 88 binary blocks
does not produce any visual change on the vessel.
8.1.3 Bit-Plane Complexity Segmentation (BPCS) Steganography
BPCS steganography is our new steganographic technique, which has a large
information hiding capacity. As have shown in the previous section, the re-
placement of the complex regions in each bit-plane of a color image with ran-
dom binary patterns is invisible to the human eyes. We can use this property
for our information hiding (or, embedding) strategy. The term information
embedding capacity is the same as information hiding capacity.
In our method we call a carrier image a vessel, cover or dummy
image. It is a color image in BMP file format, which embeds the secret infor-
mation (files in any format). We segment each secret file (already compressed
form) to be embedded into a series of blocks having 8 bytes of data each.
These blocks are regarded as 88 image patterns. We call such blocks the
secret blocks. We embed these secret blocks into the vessel image using the
following steps.
(1) Convert the vessel image from PBC to CGC system. This conversion is
executed by the exclusive-or operation [3].
(2) Segment each bit-plane of the vessel image into informative and noise-like
regions by using a threshold value (α
0
). A typical value is α
0
=0.25.
(3) Group the bytes of the secret file into a series of secret blocks.
(4) If a block (S) is less complex than the threshold (α
0
), then conjugate it to
make it a more complex block (S*). The conjugated block must be more
complex than α
0
as shown by Eq. (8.5).
(5) Embed each secret block into the noise-like regions of the bit-planes (or,
replace all the noise-like regions with a series of secret blocks). If the block
is conjugated, then record this fact in a conjugation map.
(6) Also embed the conjugation map as was done with the secret blocks.
(7) Convert the embedded vessel image from CGC back to PBC.
The Decoding algorithm (i.e., the extracting operation of the secret infor-
mation from an embedded vessel image) is just the reverse procedure of the
embedding steps.
The novelty in BPCS steganography is itemized in the following.
A) Segmentation of each bit-plane of a color image into Informative and
Noise-like regions.
B) Introduction of the B−W boarder based complexity measure (α)for
region segmentation.
C) Introduction of the conjugation operation to convert simple secret blocks
to complex blocks.
D) Using CGC image plane instead of PBC plane.
