image steganography combined with des encryption pre processing

1. Image Steganography Combined with DES Encryption Pre-processing
Yang Ren-er, Zheng Zhiwei, Tao Shun, Ding Shilei
College of Information Science and Engineering Ningbo University, Ningbo 315211, China
Abstract—In order to improve the security of
steganography, this paper studied image steganography
combined with pre-processing of DES encryption. When
transmitting the secret information, firstly, encrypt the
information intended to hide by DES encryption is
encrypted, and then is written in the image through the
LSB steganography. Encryption algorithm improves the
lowest matching performance between the image and the
secret information by changing the statistical
characteristics of the secret information to enhance the
anti-detection of the image steganography. The
experimental results showed that the anti-detection
robustness of image steganography combined with
pre-processing of DES encryption is found much better
than the way using LSB steganography algorithms directly.
Keywords-Information hiding; Steganography; DES
encryption; High security
I. INTRODUCTION
Steganography is an information hiding technique
developed in recent years. It is a procedure that makes
use of human perceptive sense of visual or aural
redundancy to digital multimedia, and that embeds the
secret information in the public media to transfer digital
media carrying confidential information to achieve
covert communications[1]
. Imperceptibility is an
important feature of steganography, also called
transparency or anti-detection performance which
includes visual imperceptibility and statistical
imperceptibility. The imperceptibility of steganography
is enhanced by improving the method of steganography[2]
,
or selecting an appropriate steganographic carrier[3]
, or
improving the matching relationship between carrier
image and secret information.
Steganography is different from traditional encryption,
which is theoretically based on cryptography to hide
communication contents by encrypting plaintext, but it is
difficult to mask the fact that communication occurred,
and ciphertext transmission will easily arouse the
attacker’s suspicions, and then it could be intercepted,
attacked or cracked. Steganography complements the
deficiency of concealment of the encryption. Through
transmitting communication contents hidden secretly in
public media, it covers up the facts of real
communication purpose and that communication
occurred. It is not a competitive relation between
steganography and encryption, but they can reinforce
each other, to further ensure the safety of covert
communication[4]
. This paper studied image
steganography based on encryption, which combines the
traditional encryption and information steganography. It
not only makes the secret information transmission
"incomprehensible" and "invisible", but makes the
steganographic system have a higher anti-detection
performance.
II. IMAGE STEGANOGRAPHY COMBINED WITH
ENCRYPTION
A. DES Encryption
DES uses a 56-bit key and an additional 8-bit parity
bit, resulting in the largest 64-bit packet size. This is an
iterative block cipher, using the technology known as the
Feistel, which will encrypt the text block half. The use of
sub-key pair, half of which application circulatory
function, and then the output with the other half to "
exclusive or" operator followed by the exchange of the
two and a half, this process will continue, but in the end
a cycle of non-exchange. DES uses 16 cycles, using xor,
replacement, substitution, four basic arithmetic shift
operations[5]
. After the hidden information is encrypted,
not only the invisibility of information is increased, but
also the statistical characteristics of the information and
the correlation between information are changed in the
same time, which makes the information become 0-1
bitstream, which is in the probability distribution. In
order to verify the characteristics of encryption algorithm,
download three English document of 32768 characters
from the Internet, and inspect the 0 -1 distribution in the
document before and after encryption. From table 1,
before the encryption, the number of 0 and 1 is not
balanced because of correlation between characters in the
natural document, but after the encryption, binary stream
of 0 s and 1 s close to equal probability distribution in
the document.
Table 1 the 0 -1 Distribution in the Document before and after
Encryption
doc
ume
nt
before the
encryption
after the
encryption
the
number
of 0
the
number
of 1
the
number
of 0
the
number
of 1
1 143674 118470 130931 131213
2 143698 118446 131218 130926
3 141719 120425 131069 131075
4 142757 119387 131665 130479
2014 Sixth International Conference on Measuring Technology and Mechatronics Automation
978-1-4799-3434-8/14 $31.00 © 2014 IEEE
DOI 10.1109/ICMTMA.2014.80
316
2014 Sixth International Conference on Measuring Technology and Mechatronics Automation
978-1-4799-3434-8/14 $31.00 © 2014 IEEE
DOI 10.1109/ICMTMA.2014.80
323
2014 Sixth International Conference on Measuring Technology and Mechatronics Automation
978-1-4799-3434-8/14 $31.00 © 2014 IEEE
DOI 10.1109/ICMTMA.2014.80
323
2014 Sixth International Conference on Measuring Technology and Mechatronics Automation
978-1-4799-3434-8/14 $31.00 © 2014 IEEE
DOI 10.1109/ICMTMA.2014.80
323
2014 Sixth International Conference on Measuring Technology and Mechatronics Automation
978-1-4799-3435-5/14 $31.00 © 2014 IEEE
DOI 10.1109/ICMTMA.2014.80
323

2. Figure 1.Frequency of sequences of 0 and 1 in the tour
B. LSB Steganography Combined with
Digital Image
The LSB (Least Significant Bit) which hides the
secret information to the least significant bit of carrier
information, is the most classic and simplest
steganography algorithm, which also features of a large
capacity and concealment. It is still widely considered
most practical and applied up to today.
The LSB steganography uses the secret information
instead of the last bit of the image pixels value, which is
equivalent to superimposing a weak signal upon the
original carrier signal, and therefore it’s difficult to
realize visually. But during the embedding process, if the
lowest bit of secret information is different from that of
pixel value, we need to change the lowest bit of pixel
value, namely change the pixel value 2i to 2i+1 or 2i+1
to 2i. The parity value transform in the LSB
steganography produces parity asymmetry. Fridirich et al.
proposed the method of using this asymmetrical parity
value transform of LSB to go on RS attack[7]
, and
Westfield et al. proposed Chi-square test[8]
to attack LSB
steganography algorithm. If steganographic method can
minimize the distortion of the histogram, it can
fundamentally resist the attack of analysis methods
aforementioned. So in this paper, we propose the
steganography combined with encryption, encrypting the
information intended to hide before the steganalysis with
encryption pre-processing, and the imperceptibility of the
steganography algorithm can be improved by reducing
the distortion of the histogram.
C. Image Steganography Combined with
Encryption
In order to improve the imperceptibility of
steganography algorithm, this paper studied the
steganography combined with encryption algorithm,
which reach the goal by changing the matching
relationship between carrier image and secret
information. At the transmitting terminal, we firstly
choose the appropriate image as the carrier, and then
encrypt text information or documents designed to hide
by DES encryption followed by using the LSB
steganography algorithm to hide the encrypted
information in the image; at the receiving terminal,
firstly extract the encrypted information from the carrier
image by the algorithm which is contrary to
steganography algorithm, and then recover the hidden
information by DES decryption algorithm.
the secret
information
carrier
image
secret key secret image
the secret
information
DES
Encryption
decryption
algorithm
LSB
imbedding
Extraction
algorithm
Figure 2.the flow chart of Image Steganography Combined with Encryption
D. The Evaluation Method of
Steganography Algorithm
1) Histogram Difference and the Sum of Histogram
absolute Difference
We denote )(nh as the image gray histogram’s
function. For the gray level image of 8 bits,
]255,0[n . And )(nh is a sequence which
represents the number of each pixel values in the image,
namely
¦¦
1
0
1
0
)),(,()(
W
i
H
j
jipnnh G (1)
Where
vu
vu
if
if
vu
z¯
®
­
,
0
,1
),(G
And )( jip indicates the image’s pixel value
at ),( ji , W is the image’s width, H is the image’s
height.
317324324324324

3. We denote )(nh as the histogram of the original
image and )('
nh as the encryption image, ]255,0[n .
Then, ][nhm denote Histogram difference, namely
][][][ nhnhnHm c (2)
¦
255
0
|)(')(|
i
ihihHae (3)
The absolute difference of histogram expresses how the
image changes before and after the steganography. The
smaller Hae is, the better imperceptibility of the
steganography is.
2) Relative Entropy of the Image before and after
Steganography (K–L divergence)
Relative entropy of the image before and after
steganography or the K–L divergence is used to measure
the security of the steganographic system put forward by
Cachin[6]
.The decrease of the K–L divergence shows the
improvement of the steganographic system’s safety
performance. If the K_L divergence is zero, the
steganographic system is absolutely safe, namely
0,)||( d HHPsPcD is absolutely safe
¦
2 5 5
0 ][
][
lo g][)||(
n s
c
c
np
np
npPsPcD (4)
Where
][npc is gray level’s probability distribution of
carrier image, ][nps is that of steganasis image.
III. EXPERIMENTAL RESULTS AND ANALYSIS
Simulation experiments embed information that
needs to hide and the information after DES encryption
respectively to 512 x 512 pixel image 1-3 by LSB
steganography algorithm. It is showed in Figure 3.
Figure3. the experimental picture
From the experimental results in Figure 3, we can see
the figure on the left, if the information is unencrypted
before the LSB algorithm , the difference between carrier
image and the steganasis image is large, if not, we can
see it from the figure on the right, the difference is small.
The smaller the histogram difference is, the better the
performance of steganographic system is.
From table 1 and its experimental results, we can also
see that after the encryption, the histogram modification
and K–L divergence decrease, suggesting that after the
encryption, the anti-interference performance of the
steganography gets better. Thus, steganography system
combined with encryption is superior to direct
steganalysis.
Figure 4. the histogram difference before and after steganography in two
ways
Table 2. steganasis image effects without encryption
Table 3. steganasis image effects with encryption
IV. CONCLUSIONS
This paper mainly probes the steganography carried by
image, which combines DES encryption with LSB
algorithm, and implements dual protect of hidden
information, making the hidden information
318325325325325

4. incomprehensible and invisible. Besides, the DES
encryption algorithm changes the statistical
characteristics of the secret information, and improves
the lowest matching degree of its bitstream and carrier
image, leading to a better imperceptibility of
steganographic algorithm.
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