VISUAL CREPTOGRAPHIC STEGNOGRAPHY IN IMAGES


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INTRODUCTION

Now a days, various modes of communication like LAN, WAN and INTERNET are widely used for communicating information from one place to another around the globe. Such communication networks are open which any one can access easily. They are regularly monitored and an intercepted.
Steganography, from the Greek, means covered, or secret writing, and is a long-practised form of hiding information. Although related to cryptography, they are not the same. Steganography's intent is to hide the existence of the message, while cryptography scrambles a message so that it cannot be understood. More precisely,
'The goal of steganography is to hide messages inside other harmless messages in a way that does not allow any enemy to even detect that there is a second secret message present."
Steganography includes a vast array of techniques for hiding messages in a variety of media. Among these methods are invisible inks, microdots, digital signatures, covert channels and spread-spectrum communications. A message is embedded in a cover media in an invisible manner so that one could not suspect about its existence.
In this paper we present a substitution based information protection method where we combine cryptographic, steganographic and signal processing concepts together for achieving security. The method is known as Steganography Based Information Protection method. In this method we substitute the information bit in randomly selected pixels at random places within LSB region.

STEGANOGRAPHY TECHNIQUE

Steganography is the art and science of communicating in a way which hides the the existence of the secret message communication. It aims to hide information /covered writing. Information to be protected is hidden in another data known as cover or carrier. Data containing hidden message are called as Steganos or Stegos. Steganos look like cover data and it is difficult to differentiate between them. Steganography based communication over easily accessible platforms to prevent leakage of information.


Kerck Off Principle:

In cryptography, this principle states that "the security of the system has to be based on the assumption that the enemy has full knowledge of the design and implementation details of the steganographic system". The only missing information for the enemy is a short, easily exchangeable random number sequence, the secret key.

STEGANOGRAPHY METHODS;


According to modification in covers, the methods can be categorized as
❖ Substitution
❖ Transform domain
❖ Spread spectrum
❖ Statistical
❖ Distortion
❖ Cover generation


Substitution Method:

It is commonly used simple method in which we can put information bits in LSB sequentially at fixed place, randomly at fixed place or randomly at random places in cover pixels. The message to be protected passes through scanning, coding, encryption process to form an embedded message.
Scanning, coding, encryption steps make the information unintelligible so that one cannot extract plain message.
Embedding make the message invisible so that one cannot detect it.
Reshaping spreads the message so that embedded message can be detected from distorted steganos by authorized receivers.
Cover processing makes detection of embedded message more difficult since the distortion is either due to noise addition or due to message embedding .
This would increases the robustness and security. Many attacks on such steganographic systems are suggested. Some attacks that can be applied are given below:
❖ Stego-Only Attack
❖ Message-Stego Attack
❖ Cover-Stego Attack
❖ Message-Cover-Stego Attack

Proposed Method:

The framework of proposed Steganography Based Information Protection method is shown in Fig 1. Its description is presented in the following steps. FRAME WORK OF SBIPM


Visual Perception:

For any steganography based secure system, the perception of steganos should be as cover image itself so that one cannot differentiate them and detect the existence of embedded message.

Difference Analysis:

The "difference-images"obtained by taking the difference between cover, processed cover and stego images are not visible. For making the difference visible in "difference-images" for visual interpretation, we first increase differences by multiplication of weight factor and then revert the values to get the strengthened
STEGANOGRAPHY
"difference-images".From analysis of these "difference-images ", on could not say that the changes are either due to cover processing or message embedding and hence we can say that the method is safe from known cover-stego attack.

Distortion Analysis:

Distortion analysis of stego images is carried out by studying distortion / similarity messages statistically. There are many methods for measuring distortion that can be used for distortion analysis. Distortion between two different images is measured by considering Mean Square Error (MSE), Mean Absolute Error (MAE) or Histogram Similarity (HS).