Enhanced Security with Cryptography & Steganography : An ImplementationByDipti Kapoor Sarmah : Enhanced Security with Cryptography & Steganography : An ImplementationByDipti Kapoor Sarmah
Introducion : Introducion Cryptography and Steganography are well known and widely used techniques that manipulate information (messages) in order to cipher or hide their existence.
Cryptography scrambles a message so it cannot be understood; the Steganography hides the message so it cannot be seen.
In this presentation we will focus to develop one system, which uses both cryptography and Steganography for better confidentiality and security.
Algorithm used for Cryptography & Steganography : Algorithm used for Cryptography & Steganography For Cryptography– AES algorithm
For Steganography- Used Frequency Domain technique
if we combine these techniques straight forwardly, there is a chance that the intruder may detect the original message. Therefore, our idea is to apply both of them together with more security levels and to get a very highly secured system for data hiding.
AES Algorithm for cryptography : AES Algorithm for cryptography This standard specifies the Rijndael algorithm , a symmetric block cipher that can process data blocks of 128 bits, using cipher keys with lengths of 128, 192, and 256 bits.
The input, the output and the cipher key for Rijndael are each bit sequences containing 128, 192 or 256 bits with the constraint that the input and output sequences have the same length but for the Advanced Encryption Standard (AES) the only length allowed is 128.
Advantages of using AES : Advantages of using AES Very Secure
Reasonable Cost.
Main Characteristics:
Flexibility
Simplicity
DCT Frequency Domain technique for Steganography : DCT Frequency Domain technique for Steganography The message is inserted into the DCT domain of the host image.
The hidden message is a stream of “1” and “0” giving a total number of 56 bits.
The transform is applied to the image as a multiple factor of 8x8 blocks.
The DCT is to select the 56 larger positive coefficients, in the low-mid frequency range.
The selected coefficients ci are ordered by magnitude and then modified by the corresponding bit in the message stream.
If the i-th message bit s(i) to be embedded is “1”, a quantity D is added to the coefficient. This D quantity represents the persistence factor. If the message bit is “0”, the same quantity is subtracted from the coefficient. Thus the replaced DCT coefficients are DCT (new) = DCT+1*D for s(i)=1Else DCT (new) =DCT-1*D for s(i)=0. : If the i-th message bit s(i) to be embedded is “1”, a quantity D is added to the coefficient. This D quantity represents the persistence factor. If the message bit is “0”, the same quantity is subtracted from the coefficient. Thus the replaced DCT coefficients are DCT (new) = DCT+1*D for s(i)=1Else DCT (new) =DCT-1*D for s(i)=0.
Advantages of using frequency domain Steganography : Advantages of using frequency domain Steganography Very secure, hard to detect
Flexible, different techniques for manipulation of DCT coefficients values
How the combination works? : How the combination works? We design the system with three modules-
For Cryptography - Crypto Module
For Steganography - Stego Module
For extra security - Security Module
The extra security module that we are providing make this system highly secured. The process flow for the system is as follows-
Hiding the Text : Hiding the Text
1. Crypto Module : 1. Crypto Module Insert text for encryption.
Apply AES algorithm using 128 bit key (Key 1).
Generate Cipher Text in hexadecimal form
Crypto Module-Figure : Crypto Module-Figure
2. Security Module : 2. Security Module This is an intermediate module which provides an extra security features to our newly developed system.
This module is used to modify the cipher text and to generate two extra keys.
Before the hiding process this module works as follows:
Separate the alphabets and digits from the cipher text.
Keep track of the original position of the alphabet and the digits in the form of a secret key (Key 3).
Separate first seven alphabets retrieved from first step and add the remaining alphabets at the end of the separated digits as in the first step. This generates the second key (Key 4).
Security Module-Figure : Security Module-Figure
3.Stego Module : 3.Stego Module For Stego Module the following steps are considered :
Take seven alphabets from the above discussed Security Module.
Scramble the alphabets using a 64 bit key (Key 2).
Take a Gray Scale Image.
Find the DCT of the Image
Hide the Cipher by altering DCTs.
Apply Inverse DCT.
Find the Stego Image.
Stego Module-Figure : Stego Module-Figure Take a Gray
Scale
Image
Retrieving Text : Retrieving Text
1.Stego Module (Reverse Process) : 1.Stego Module (Reverse Process) For Stego Module the following steps are considered for retrieving the cipher text :
Take DCT of the Original Image.
Take DCT of the Stego Image.
Take difference of DCT coefficients.
Retrieve bits of the hidden seven alphabets from LSB of the DCT.
Construct the distorted seven alphabets.
Unscrambled the distorted seven alphabets using Key 2.
Retrieve the original seven alphabets.
Stego Module (Reverse Process)-Figure : Stego Module (Reverse Process)-Figure
2. Security Module (Reverse Process) : 2. Security Module (Reverse Process) For Security Module the following steps are considered for retrieving the cipher text :
Club the seven characters with the alphabets of Key 4.
Using Key 3 and Key 4 reconstruct the cipher text from alphabets and digits.
Security Module (Reverse Process)-Figure : Security Module (Reverse Process)-Figure Seven alphabets retrieved from reverse Stego Module
3.Crypto Module (Reverse Process) : 3.Crypto Module (Reverse Process) For Crypto Module the following steps are considered for retrieving the original text.
Get the above retrieved cipher text.
Reverse AES algorithm by using Key 1.
Get the original message.
Crypto Module (Reverse Process)-Figure : Crypto Module (Reverse Process)-Figure
Proposed System : Proposed System
Hiding Text : Hiding Text Generate the cipher text in hexadecimal form by AES algorithm, in the form of alphabets (A, B, C, D, E, F) and digits (0, 1, 2, 3, 4, 5, 6, 7, 8, 9).
Separate the alphabets and digits with the help of Separator 1 and keep track of the original position of the alphabets and digits in the form of the first key (Key 1).
Take the first 7 characters of the alphabets; this part will be hidden in the image.
Take the rest of the alphabets and combine with the digits; this will form the second key (Key 2). : Take the rest of the alphabets and combine with the digits; this will form the second key (Key 2). Hide the 7 characters in the Image
Proposed System for hiding text :Figure : Proposed System for hiding text :Figure
Retrieving Text : Retrieving Text Retrieve the 7 characters from the image .Separate alphabets and digits from Key 2 with the help of Separator 2.
Add back the rest of the alphabets from Key 2 to 7 characters retrieved from the image.
Reorganize the alphabets and digits with the help of the Key 1 to get back the original cipher text in hexadecimal form.
Regenerate the original text message from the cipher text with the help of AES algorithm
Proposed System for retrieving text :Figure : Proposed System for retrieving text :Figure
How secure the proposed system is? : How secure the proposed system is? The proposed solution is highly secure because-
It’s a combination of two highly secured techniques -
AES for cryptography
DCT manipulation for Steganography.
Number of Keys: This system contains total 4 keys.
One 128 bits private key for AES algorithm
One 56 bits private key for scrambling the cipher text.
Two extra private generated keys for retrieving the original message.
Conclusion : Conclusion In this presentation I have presented a new system for the combination of cryptography and Steganography using four keys which we have proven that our new system is more secure in comparison to other developed methods.
Steganography, especially combined with cryptography, is a powerful tool which enables people to communicate without possible eavesdroppers even knowing there is a form of communication in the first place. The proposed method provides acceptable image quality with very little distortion in the image.
The main advantage of this Crypto/Stego System is that the method used for encryption, AES, is very secure and the DCT transformation Steganography techniques are very hard to detect.
References : References D.R. Stinson, Cryptography: Theory and Practice, Boca Raton, CRC Press, 1995. ISBN: 0849385210
Provos, N. and Honeyman, P. (2003). Hide and seek: An introduction to steganography. IEEE SECURITY & PRIVACY
Chandramouli, R., Kharrazi, M. & Memon, N., “Image Steganography and steganalysis: Concepts and Practice”, Proceedings of the 2nd International Workshop on Digital Watermarking, October 2003
Jamil, T., “Steganography: The art of hiding information is plain sight”, IEEE Potentials, 18:01, 1999
Marvel, L.M., Boncelet Jr., C.G. & Retter, C., “Spread Spectrum Steganography”, IEEE Transactions on image processing, 8:08, 1999
Bender, W., Gruhl, D., Morimoto, N. & Lu, A., “Techniques for data hiding”, IBM Systems Journal, Vol 35, 1996
N. F. Johnson and S. Katzenbeisser, .A survey of steganographic techniques., in S. Katzenbeisser and F. Peticolas (Eds.): Information Hiding, pp.43-78. Artech House, Norwood, MA, 2000.