Steganography: A Technique for Covert Data Communication

The word Steganography is derived from Greek:

• Steganos → Covered or hidden

• Graphia → Writing

Unlike cryptography, steganography hides the presence of information, not just the content.

Steganography System Components

Typical components of a steganographic system include:

 1. Medium Cover

The original data-hiding file
Examples include text, music, video, images, and network packets.

 2. Covert Communication

The private information to be concealed
Text, image, audio, key, and virus are a few examples.

 3. Stego-Key (Optional)

A hidden key that regulates extraction and embedding

 4. The Stego-Object

Final result with concealed information

General Working Principle

1. Select a cover file

2. Convert secret data into binary form

3. Embed data using an algorithm

4. Generate stego file

5. Receiver extracts data using correct key

Classification of Steganography Techniques

A. Image Steganography (Most Widely Used)

Images contain large redundant data, making them ideal for hiding information.

 Image Formats Used

• BMP

• PNG

• JPEG (with DCT-based methods)

(i) Spatial Domain Techniques

 LSB (Least Significant Bit) Method

• Least significant bits of pixel values replaced with secret data bits

• Minimal perceptible change

 Example (8-bit grayscale):

 High capacity
 Vulnerable to compression and filtering

(ii) Transform Domain Techniques

Used in compressed images like JPEG.

 DCT (Discrete Cosine Transform)

• Data hidden in frequency coefficients

• More robust than LSB

 Resistant to compression
 Complex implementation

(iii) Masking and Filtering

• Similar to watermarking

• Data embedded in significant areas

 Robust
 Low data capacity

B. Audio Steganography

Human auditory system (HAS) is less sensitive to slight sound changes.

Techniques:

• LSB Coding

• Phase Coding

• Echo Hiding

• Spread Spectrum

 Hard to detect
 Data loss after compression

C. Video Steganography

Combination of:

• Image steganography (frames)

• Audio steganography (sound)

 Very high capacity
 High security
 Requires large processing power

D. Text Steganography

Least secure and least used.

Techniques:

• Extra spaces

• Font variations

• Capitalization patterns

• Synonym substitution

 Easily detectable
 Simple implementation

E. Network Steganography

Data hidden in:

• IP header fields

• TCP sequence numbers

• Packet timing delays

 Real-time covert communication
 Highly complex

 Used in cyber espionage & malware communication.

Steganography vs Cryptography vs Watermarking