Information Hiding – Steganography
Steganography Types and Techniques

Abstract— Information hiding has been one of the most crucial element of information technology in recent years. Unlike Cryptography, Steganography does not only keep the content of information secret, its also keeps the existence of the information secret. This is achieved by hiding information behind another information. This paper gives an overview of Steganography and its techniques, types, and also its advantages and disadvantages.

Keywords-component; steganography; information hiding; security; confidentiality; techniques.

INTRODUCTION

Steganography help hides the fact that communication is taking place by hiding some information behind another information thereby making the communication invisible. The origin of the word “steganography” is from the Greek words “steganos” and “graphia” which is interpreted as “covered” and “writing” respectively thereby defining steganography as “covered writing”. Steganography and cryptography are both part of information hiding but neither alone is without flaws. The goal of steganography is defeated once the hidden message is found or noticed even while still in the original message (carrier). For safely transmission of hidden messages or information in steganography, multimedia files like audio, video and images are mostly used has the carrier or cover source.

METHODOLOGY

The Methodology used for this paper is based on the knowledge derived through online resources such as online publications, journals and research papers.

ORIGIN OF STEGANOGRAPHY

As information hiding techniques is receiving enormous attention lately, it was also used way back in Greece. Herodotus, a Greek historian said Histiaeus, the famous Greek tyrant used unexpected method in sending a message to his son-in-law while he was in the prison. Histiaeus shaved a slave’s head and inscribe a message on his scalp. As soon as hair grew back on the slave’s head, Histiaeus then sent him off to his son-in-law. The content of the message tattooed on the slave is not only hidden, its existence is also kept secret. Herodotus also talked about a soldier called Demeratus, who secretly needed to inform Sparta about Xerxes intentions to invade Greece. During those periods, wax-covered tablet was used as the writing medium. The message will be written directly on the wax and it will be sent to the recipient. Demeratus scraped the wax away from the wax-covered tablet, then inscribed the message on the wood beneath the wax. He then covered the wood back with wax to make it look like a blank wax-covered tablet and send to Sparta. Even if an attacker hijacked the wax-covered tablet, it will be useless because they will see it as a blank tablet. Another method of steganography used back then was the use of invisible inks. Ancient Romans uses available substances such as urine, milk and juices as invisible inks to write between lines. Once heated, the substance will darken, thereby becoming readable. Chemically produced sympathetic inks were later developed to be used as invisible inks. During World War II, invisible inks were used to convey hidden messages between lines of letters that may appear innocent when intercepted. Invisible inks are still in use mostly as anti-counterfeit practice. For example, some ink becomes legible when placed under ultraviolet light. An example is the word "VOID" printed on official documents like checks that appear when placed under ultraviolet lights like photocopying.

TYPES OF STEGANOGRAPHY

In steganography, information is mostly hidden in digital media. Media files are perfect for information hiding because of their large sizes. The techniques used in digital steganography will also be discussed in this paper. Discussed below are the types of digital steganography.

1 Audio Steganography

Audio steganography entails hiding messages or information in audio files. This method involves hiding data in MP3, WAV and AU audio files.

2 Text Steganography

Text Steganography entails hiding information inside the text files. When Text steganography is used, the hidden data is placed behind every nth letter of every words in the original text message. Text steganography proved to be one of the most difficult type of steganography due to the absence of redundancy in a text compared to audio or image. Text steganography however has an advantage which is its smaller memory usage.

3 Video Steganography

Since video files consists of images and sounds, video steganography uses both the techniques of images and sounds. Video steganography however has an essential advantage over other types, which is large quantity of data can be hidden inside the video because it contains active streams of images and sounds. Any distortions can hardly be noticed by humans due to the continuous flow of information. Video formats supported by video steganography include but not limited to Mp4, MPEG, AVI.

4 Image Steganography

In image steganography, messages or information is hidden inside a particular image. The least significant bit (LSB) of some bytes or all of the bytes of the image is tweaked to bit of the hidden message. Image steganography is widely used in digital steganography because there are lots of bit present representation of an image digitally.

[pic]
Figure 1: This is an example of how messages can be hidden in an image file. The above image contains the message “This is my Cryptography Term Paper” and can be decrypted at http://mozaiq.org/decrypt using “concordia” as the password.

5 Network or Protocol Steganography

Network or Protocol Steganography involves hiding messages or information inside the network protocols. Example of network protocols that can serve as the carrier of the information includes Transmission Control Protocol(TCP), Internet Protocol (IP), Internet Control Message Protocol (ICMP) AND User Datagram Protocol (UDP). Information can be embedded in the header of TCP segment or IP packet in some optional fields.

STEGANOGRAPHY TECHNIQUES

A good Steganography technique protects hidden data against loss due to scaling, modification, compression, interception, removal or modification etc. and also ensure the hidden information remains untouchable and recoverable. Below are the techniques used in steganography. A. Spatial Domain Technique
In this technique, the hidden information is placed directly in the pixels. Some pixel values of the carrier image are altered when hiding information. This technique can further be divided into the following categories: • Least Significant Bit (LSB) • Pixel Value Differencing (PVD) • Edges Based Embedding method (EBE) • Random Pixel Embedding method (RPE)

B. Spread Spectrum Technique
In Spread Spectrum Technique, the hidden information is distributed over a wide frequency bandwidth. The proportion of the signal to noise must be small to make it difficult or impossible to discover the existence of the hidden information. When this technique is used, it is difficult to remove the hidden information completely without absolutely destroying the original original file. This technique is mostly used in military communications because of its robustness.

C. Statistical Technique
In statistical technique, hidden information is attached to the original file (i.e. the carrier) by altering several properties of the carrier. The carrier file is divided into blocks and the message to be hidden is attached to each block in bits.

D. Transform Domain Technique
In Transform Domain Technique, the hidden message is attached in the frequency domain of the original file. Transform domain technique is a more complex way of hiding information in an image. Diverse algorithms and transformations are applied on the image file to hide the information in it. This technique is further classified into the following: • Discrete Fourier Transformation (DFT) • Discrete Cosine Transformation (DCT) • Discrete Wavelet Transformation (DWT)

E. Distortion Technique
In Distortion Technique, the hidden message is stored by distorting the signal. A series of modification is administered to the original file by the encoder. On the receiving end, the encoder calculates the differences between the original file and the distorted file to detect the series of modifications therefore recover the hidden message.

CONCLUSION

Stenography has been around for years and still has a very important place in the future of information hiding. Steganography is not a replacement for cryptography. Although steganography and cryptography defers with regards to their functions, using the techniques of steganography together with cryptography to secure information creates multiple layers of security. This can be achieved by encrypting the hidden message before its embedded in the original file (carrier).

ACKNOWLEDGEMENT

I acknowledged Prof. Ron Ruhl for introducing the concept of steganography to me and also for his percipient lectures on the course as a whole. These geared up my interest in steganography.

REFERENCES

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