Given the amount of data that is being generated and transmitted electronically in the world today, it’s no surprise that numerous methods of protecting that data have evolved. One of the rapidly growing methods is steganography. In this steganography tutorial, we will cover steganography in detail.
What is Steganography?
The diagram below depicts a basic steganographic model.
As the image depicts, both cover file(X) and secret message(M) are fed into steganographic encoder as input. Steganographic Encoder function, f(X,M,K) embeds the secret message into a cover file. Resulting Stego Object looks very similar to your cover file, with no visible changes. This completes encoding. To retrieve the secret message, Stego Object is fed into Steganographic Decoder.
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Steganography Tutorial: Historical Background
Steganography is the practice of concealing a secret message behind a normal message. It stems from two Greek words, which are steganos, means covered and graphia, means writing. Steganography is an ancient practice, being practiced in various forms for thousands of years to keep communications private. For Example:
- The first use of steganography can be traced back to 440 BC when ancient Greece, people wrote messages on wood and covered it with wax, that acted as a covering medium
- Romans used various forms of Invisible Inks, to decipher those hidden messages light or heat were used
- During World War II the Germans introduced microdots, which were complete documents, pictures, and plans reduced in size to the size of a dot and were attached to normal paperwork
- Null Ciphers were also used to hide unencrypted secret messages in an innocent looking normal message
Now, we have a lot of modern steganographic techniques and tools to make sure that knows our data remains secret. Now you might be wondering if steganography is same as cryptography. No, they are two different concepts and this steganography tutorial presents you the main differences between them.
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How is Steganography different from Cryptography?
At their core, both of them have almost the same goal, which is protecting a message or information from the third parties. However, they use a totally different mechanism to protect the information.
Cryptography changes the information to ciphertext which cannot be understood without a decryption key. So, if someone were to intercept this encrypted message, they could easily see that some form of encryption had been applied. On the other hand, steganography does not change the format of the information but it conceals the existence of the message.
STEGANOGRAPHY | CRYPTOGRAPHY | |
Definition | It is a technique to hide the existence of communication | It’s a technique to convert data into an incomprehensible form |
Purpose | Keep communication secure | Provide data protection |
Data Visibility | Never | Always |
Data Structure | Doesn’t alter the overall structure of data | Alters the overall structure of data |
Key | Optional, but offers more security if used | Necessary requirement |
Failure | Once the presence of a secret message is discovered, anyone can use the secret data | If you possess the decryption key, then you can figure out original message from the ciphertext |
So, in other words, steganography is more discreet than cryptography when we want to send confidential information. The downside being, the hidden message is easier to extract if the presence of secret is discovered. For the remainder of this steganography tutorial, we will learn about different steganography techniques and tools.
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Steganography Techniques
Depending on the nature of the cover object(actual object in which secret data is embedded), steganography can be divided into five types:
- Text Steganography
- Image Steganography
- Video Steganography
- Audio Steganography
- Network Steganography
Let’s explore each of them in detail.
Text Steganography
Text Steganography is hiding information inside the text files. It involves things like changing the format of existing text, changing words within a text, generating random character sequences or using context-free grammars to generate readable texts. Various techniques used to hide the data in the text are:
- Format Based Method
- Random and Statistical Generation
- Linguistic Method
Image Steganography
Hiding the data by taking the cover object as the image is known as image steganography. In digital steganography, images are widely used cover source because there are a huge number of bits present in the digital representation of an image. There are a lot of ways to hide information inside an image. Common approaches include:
- Least Significant Bit Insertion
- Masking and Filtering
- Redundant Pattern Encoding
- Encrypt and Scatter
- Coding and Cosine Transformation
Audio Steganography
In audio steganography, the secret message is embedded into an audio signal which alters the binary sequence of the corresponding audio file. Hiding secret messages in digital sound is a much more difficult process when compared to others, such as Image Steganography. Different methods of audio steganography include:
- Least Significant Bit Encoding
- Parity Encoding
- Phase Coding
- Spread Spectrum
This method hides the data in WAV, AU, and even MP3 sound files.
Video Steganography
In Video Steganography you can hide kind of data into digital video format. The advantage of this type is a large amount of data can be hidden inside and the fact that it is a moving stream of images and sounds. You can think of this as the combination of Image Steganography and Audio Steganography. Two main classes of Video Steganography include:
- Embedding data in uncompressed raw video and compressing it later
- Embedding data directly into the compressed data stream
Network Steganography (Protocol Steganography)
In today’s digitalized world, various software tools are available for Steganography. In the remainder of this Steganography Tutorial, we will explore some of the popular steganographic tools and their capabilities.
Best Tools to Perform Steganography
There are many software available that offer steganography. Some offer normal steganography, but a few offer encryption before hiding the data. These are the steganography tools which are available for free:
- Stegosuite is a free steganography tool which is written in Java. With Stegosuite you can easily hide confidential information in image files.
- Steghide is an open source Steganography software that lets you hide a secret file in image or audio file.
- Xiao Steganography is a free software that can be used to hide data in BMP images or in WAV files.
- SSuite Picsel is another free portable application to hide text inside an image file but it takes a different approach when compared to other tools.
- OpenPuff is a professional steganographic tool where you can store files in image, audio, video or flash files
Well, these are few tools to perform steganography. There are many other different tools with different capabilities. However, you will get the desired results from these tools.
So, we have reached the end of Steganographic Tutorial. Steganography was developed for secure communication. However, criminals and terrorist organizations are using this for their own purpose. So, understanding how to hide data steganography, and prevent that data from being misused, can be very helpful for both attack and defense.
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