A novel secure combination technique of steganography and cryptography

International Journal of Information Technology, Modeling and Computing (IJITMC) Vol. 2, No. 1, February 2014
DOI : 10.5121/ijitmc.2014.2105 55
A Novel Secure Combination Technique of
Steganography and Cryptography
Pye Pye Aung1
and Tun Min Naing2
1
University of Technology (Yatanarpon Cyber City), Pyin Oo Lwin, Myanmar
2
Computer University (Pathein), Myanmar
ABSTRACT
A new technique proposed with the combination of cryptography and steganography enhanced with new
secure feature for generating a new security system. Cryptography and Steganography are two popular
ways for secure data transmission in which the former distorts a message so it cannot be understood and
another hides a message so it cannot be seen. In cryptography, this system is used advanced encryption
standard (AES) algorithm to encrypt secret message and then these are separated keys; one of which is
used to hide in cover image. In steganography, a part of encrypted message as a key is used to hide in
discrete cosine transform (DCT) of an image which is highly secured. This kind of system is to be
introduced in applications such as transferring secret data that can be authentication of various fields.
KEYWORDS
Cryptography, DCT Coefficient, Hiding Text, Steganography, Stego- image
1. INTRODUCTION
In networking, cryptography can be specified as the security service for data and
telecommunications. Cryptography is an important way to address message transmission security
requirements. Encryption and decryptiong of messages are made for the technique of
cryptography. A mechanism of hiding the original messages from the intruders and by making a
suspect of the existence of the message only to the intended receiver is called steganography.
Here the secret message is sent as image or text through the encryption of the message in which
special keys are arranged for those intended receivers to get the original message. The receiver
only makes actual procedure of the real message sent by the sender. Real message can be letters
or digits which can be encrypted as hidden message in any form as audio or video or image [3].
Steganography must not be confused with cryptography, where the message is transformed so as
to make its meaningless to malicious people who intercept it. The goal of steganography is to
avoid drawing suspicion to the transmission of the secret message between sender and receiver. A
secure data transmission is made using cryptography and steganography. Combination of both
these two techniques results in appearing a highly secured method for data communication.

56
2. BACKGROUND THEORY
Cryptography can be specified as the security service including authentication, privacy and
confidentially. In this paper we have used AES algorithm in cryptography. The three types of
algorithms are described:
(i) Secret Key Cryptography (SKC): Uses a single key for both encryption and decryption.
(ii)Public Key Cryptography (PKC): Uses one key for encryption and another for
decryption.
(iii)Hash Functions: Uses a mathematical transformation to irreversibly "encrypt" information
[6].
Steganography is a mechanism for hiding and retrieving the high sensitive information in data
transmission. Steganography must not be confused with cryptography, where the message is
converted its meaningless to malicious people who intercept it. The main goal of steganography
techniques is that it is diffilcult to detect the image and so saved from attacks. The steganography
approaches can be distinguished into three types: pure steganography, secret key steganography
and public key steganography.
2.1. AES algorithm for Cryptography
Advanced Encryption Standard (AES) is a standard for the encryption of electronic data. The U.S.
government held in 1997 and now use in worldwide. AES is a symmetric-key algorithm which
means that the same key is used both of sender and receiver. This AES standard specifies the
Rijndael algorithm [1], a symmetric block cipher that can process data blocks of 128 bits, using
key size of 128, 192, and 256 bits. The input, the output and the cipher key are used in Rijndael. It
takes an input and output of certain block size, only 128 bits.
2.1.1. Advantages of using AES algorithm
1. Very Secure.
2. Reasonable Cost.
3. Main Characteristics:
I. Flexibility, II. Simplicity.
2.2. DCT - frequency domain algorithm for Steganography
The hidden message is a stream of “1” and “0” giving a total number of 80 bits to insert the secret
message into the DCT domain of the cover image. The color-based transformation converts the
image (cover image) into 8x8 blocks of pixels. Next, at least 80 larger positive coefficients need
to embed in the cover image in the low-mid frequency range. DCT can divide the image into
high, middle and low frquency components. As the high frequency coefficients are vulnerable and
less robust on the quality of image. The main issue of this work is robustness against with high
quality of image, thus the low and mid frequency coefficients are the most appropriate. The
selected coefficients ci are modified by the corresponding bit in the message stream. This K
quantity represents the persistence factor. As soon as the ith term of message bit s(i) is “1”, the
coefficient of the image is added with a quantity K; otherwise the same quantity is subtracted
form it. Thus the replaced DCT coefficients are
DCT (new) = DCT+1*K for s(i)=1;
Else DCT (new) = DCT-1*K for s(i)=0.

57
2.2.1. Advantages of using frequency domain Steganography
1. Very secure, hard to detect
2. More flexible, different techniques for calculation of DCT coefficients values
3. PROPOSED COMBINING TECHNIQUE
In cryptography, this system is used AES algorithm with its symmetric key and the cipher text is
converted into two extra keys for high security, then the steganography is implemented to the key
(3) to get stego image. The system is designed with three creation steps to hide the text –
(a) For Cryptography – Crypto Creation Step
(b) For Steganography – Stego Creation Step
(c) For Extra Securtiy – Security Creation Step
3.1. Crypto Creation Step
For Crypto Module, the following steps are applied for encrypting the data (Refer Figure1):
(a) Insert text for encryption.
(b) Apply AES algorithm using 128 bit key.
(c) Convert cipher text into types of format Hexadecimal, based 64 string and ASCII code
respectively.
Figure 1. Crypto Creation Step
3.2. Security Creation Step
This security module works as follows: (Refer Figure2)
(a) Create array and allocate all the position points of digit (1) from the cipher text.
(b) Remove all the positions points of digit (1) from the cipher text and the remaining
characters and digits are going to transform as modified cipher text.
(c) Remove the first ten allocated position of digit (1) among all digit (1) positions array and
generate as a secret key (key 2).
(d) Take first ten allocated position points of digit (1) from all position points of digit (1)
array and these ten digit(1) will be changed into the form of a secret key key(3).
Insert Text AES Method using Key1
Convert Cipher Text into
Hexadecimal, Based64 String
and ASCII code

58
Figure 2. Security Creation Step
3.3. Stego Creation Step
For Stego Module, the following steps are discussed for hiding the above generated cipher text
(Refer Figure3).
(a) Take the first ten allocated position points of digit (1) from the above discussed Security
Module.
(b) Scramble the first ten allocated position points of digit (1) using a 64 bit key (Key 3).
(c) Take a Color Image.
(d) Find the DCT of the Image using color transformation.
(e) Hide the Cipher by altering DCTs.
(f) Apply Inverse DCT.
(g) Find the Stego Image.
Figure 3. Stego Creation Step
4. PROPOSED SYSTEM IMPLEMENTATION
This system is developed in Visual Studio C# platform, mainly three creation steps involved –
(a) Crypto Creation Step – AES Implementation Step
(b) Security Creation Step – Newly Developed Technique
(c) Stego Creation Step – DCT Techniques Implementation Step
Generate Key2 by removing
the first ten allocation points
from the original positions of
digit (1) array from cipher text
Create array and
allocate all the
positions of digit (1)
from the cipher text
Cipher Text in
Hexadecimal, Based64
String and ASCII code
Take first ten allocation
points of digit (1) and
generate as Key3 to be
hidden
Generate modified cipher text
without being digit ole(1)
First ten allocation
points of digit (1) from
the Security Module
Scramble the text
using a Key3
Hide the first ten
allocation points of
digit (1) by altering
DCT
Stego Image Inverse DCT
Find the DCT
of the image
Take a Color Image

59
4.1. Algorithm for the proposed system
The steps of the algorithm for hiding text and retrieving text are discussed below (Refer Figure4
& Figure5).
4.1.1. Hiding Text
(a) Encrypt the original message into cipher text by using AES algorithm with symmetric
key of key 1.
(b) Convert the cipher text into Hexadecimal format in the form of alphabets (A to F) and
digits (0 to 9), Based 64 string format in the form of alphabets small letter (a to z),
capital letter (A to Z), digits (0 to 9) and two arithmetic character (+/-) and ASCII code
format of (256) characters respectively.
(c) Create array and allocate all the position points of digit (1) from converted cipher text and
remove the first ten allocated points of all digit (1) positions and then generate the key
(Key 2).
(d) Take the first ten allocated position points of digit (1) from array of cipher text and
generate it as the third key (Key 3); this part will be hidden in the image.
(e) The cipher text without having digit (1) will be remained as modified cipher text.
(f) Hide the first ten allocated position points of digit (1) in the image and get Stego-Image.
Figure 4. Proposed System for Hiding Text
Take first ten allocation points of
digit (1) from the digit (1) array
of cipher text
Create array and
allocate all the
positions of digit (1)
from the cipher text
Generate Cipher text
using AES algorithm
Remaining of all allocation
points of digit (1) array after
removing the first ten points
Remove all the position
points of digit (1) from
the original cipher text
First ten allocation points of digit (1)
Hide first ten allocation points of
digit (1) in image
Stego Image
Key2
Key3

60
4.1.2. Retrieving Text
Figure 5. Proposed System for Retrieving Text
(a) Retrieve the first ten allocated position points of digit (1) from the image and unscramble
it with Key 3.
(b) Add back the first ten position points of digit (1) into its all position points of digit (1)
using Key 2.
(c) Add back all position points of digit (1) to the modified cipher text in order to get the
original cipher text in Hexadecimal, Based 64 string and ASCII form.
(d) Reconstruct the original text message from the cipher text using AES algorithm and its
key (Key 1).
4.1.3. Security Properties of Proposed System
The proposed system is highly secure because it is a combination of AES algorithm of encryption
technique and DCT of message embedding technique. And also including two extra keys make
the system highly secured. This system contains total 3 keys.
(a) One 128 bits symmetric key for AES algorithm
(b) Two 8 bits (1 byte) generated keys for scrambling the cipher text and retrieving the
original message.
Key2
Stego Image Retrieve first ten allocation
points of digit (1)
Key3
Key1
Club first ten allocation
points of digit (1) and rest
of the digit (1) array
Retrieve the original
text message
Reconstruct the
cipher text
Add all the position points
of digit (1) to the original
cipher text
Key2
and
Key3

61
5. RESULTS
In this system, it can be compared our proposed system by using three kinds of encoding format
type. They are Hexadecimal, Based-64 and ACSII code. Encryption time will be generated as
different using three encoding format. Among them, ACSII encoding format is most efficient for
large plaintext message to encrypt. But Hexadecimal encoding format will be taken more
encryption time than any other format and so it can be used if the message size is small. As
concerned with Based-64 encoding format is appropriate message size from below results. This
paper shows the comparison of three encoding format in different messages in Figure6 and
Figure7.
Figure 6. Key Separating time in Different Messages (20-100 Kb)
0
100
200
300
400
500
600
20 40 60 80 100
Time(ms)
Message (Kb)
Hexadecimal Format
Based-64 String Format
ASCII Format
0
100
200
300
400
500
600
100 200 300 400 500
Time(ms)
Message (Kb)
Hexadecimal Format
Based-64 String Format
ASCII Format

62
6. CONCLUSION
In this thesis, a new digital message hiding system is proposed for the combination of
cryptography and steganography using three keys and modified cipher text. The combination of
these two techniques satisfies the requirements such as highly security and robustness between
sender and receiver. The proposed method ensures acceptable image quality with very little
distortion in the image. The main advantage of this system is that the method used for AES
algorithm which is very secure and the DCT transformation technique is very hard to detect in
image steganography. It also produces efficient robustness of stego-image though it had been
attacked by other techniques and additionally saved from attacks. Goal of this paper is to develop
a new security system that messages cannot be retrieved easily from the image by any attackers or
hackers in the communication process.
REFERENCES
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Journal of Advanced Research in Computer Science and Software Engineering, Volume 2, Issue 4,
April 2012.
[3] A Novel Information Security Scheme using Cryptic Steganography B. Raja Rao et. al. / Indian
Journal of Computer Science and Engineering Vol. 1 No. 4 327-332.
[4] G. Ulutas, M. Ulutas and V. Nabiyev, “Distortion free geometry based secret image sharing”,
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[6] B. E. Carvajal-Gámez , F. J. Gallegos-Funes and J. L. López-Bonilla, “Scaling Factor for RGB
Images to Steganography Applications”, Journal of Vectorial Relativity, Vol.4, No.3 pp.55-65, 2009.
[7] Domenico Daniele Bloisi, Luca Iocchi: Image based Steganography and cryptography, Computer
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[8] X. Li and J. Wang, “A steganographic method based upon JPEG and particle swarm optimization
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