Question

Steganography

Describe substitution, Mon alphabets, and other classes, and attacks

Answer 1

Steganography is data hidden within data. Steganography is an encryption technique that can be used along with cryptography as an extra-secure method in which to protect data.

Steganography techniques can be applied to images, a video file or an audio file.

The purpose of steganography is covert communication to hide a message from a third party. This differs from cryptography, the art of secret writing, which is intended to make a message unreadable by a third party but does not hide the existence of the secret communication.

Substitution:-

This system substitutes redundant or least significant parts of a cover with a secret message. Receiver can extract the information if the position where secret information has been embedded is known.

A. Least Significant Bit Substitution:-

This method is performed by substituting the least significant bit (LSB) of cover-element with the bit of a secret message . To reconstruct the secret message, the LSB of the selected cover-elements are extracted and lined up. By using this method, information can be hidden with little impacts to the carriers. Because of the simplicity of applying it into image and audio, this method is now common to steganography.

B. Random Interval:-

A pseudo random number generator is used in this method to spread the secret message over the cover-elements in a rather random manner . Both sender and receiver share a stegokey as a seed for a random number generator. A random sequence is created in which the interval between two embedded bits is determined pseudorandomly. The secret message bits are stored according to the interval between two embedded bits.

C. Pseudorandom Permutation:-

Distribution of the secret message is done in random manner over the whole cover-elements. The main goal is to increases the complexity for an attacker because there is no guarantee that subsequent message bits are embedded in the same order. A sequence is generated using a pseudorandom number generator. The secret message bits are stored according to bit position of cover-elements which is determined by the generated sequence.

D. Cover-regions and Parity Bits:-

A stego-key is used as the seed to generate pseudorandom sequence of disjoint cover-regions. Cover-region length is calculated by dividing the cover image length with the message length. Only one bit of the secret message is stored in a whole cover-region rather than in a single element. In the embedding process, disjoint cover-regions are selected, each encoding one secret bit in the parity bit. A parity bit of a region can be calculated by counting total number of 1's and modulo the value with two. One LSB of a random chosen cover-element is flipped if the parity bit of the cover-region does not match with the secret bit to encode. The parity bits of all the selected cover-regions are calculated and lined up to reconstruct the message at the receiver.

Mono Alphabets:-

Mono-alphabetic: use a single alphabet for substituting single alphabet in original text .

1) substitution can be fixed.(or)

2) Arbitrary substitution: one element maps to any other element I n element alphabet allows n! permutations or keys I

Other Classes:-

APPLICATIONS:-

1)Secret data storing

2) E-Commerce

3) Media

4) Database Systems

5) Digital Watermarking

6) Protection of data alteration

7) Confidential Communication

some more methods used in steganography:-

Audio Steganography :-

It involves hiding the data in the audio files. This method hides the data in MP3 files. First the storage environment or digital representation of the signal that will be used for the transmission of the signal and second the transmission pathway the signal might travel

Echo Hiding:

It inserts the secret data in a sound document by bringing the echo into the discrete signal. Just a single bit of secret data could be encoded if just a single resound was created from the first signal. It has focal points of giving the higher transmission rate and predominant robustness.

Advantages– It is resilient to the lossy data compression algorithms used in this method.

Disadvantages:-It provides low security and capacity.

Spacial Domain Methods:

This is the technique in which the secret information is embedded in the force of pixels(in images). It implies a few pixels are changed directly while concealing the data.

Attacks:-

Following is the list of some possible attacks:

1) File only

In this , the attacker have access to the file and should determine whether the data is hidden in it or not.

2) File and Original Copy

If the attacker have a copy of the original file and pre-encoded file then the real question is what the attacker will do with the secret message (destroy hidden information, extract hidden information , replace it).

3) Compression Attack

One of the simplest attack is to compress the file containing the hidden information. Compression algorithms try to remove the extraneous information from a file, and ―hidden‖ is equivalent to ―extraneous‖.

4) Destroy Everything Attack

In this, attacker could simply replace the whole message.

5) Reformat Attack

One of the possible attack is to change the format of the file. Different file formats don’t store the data exactly in the same way (JPEG, GIF).

6) Random Tweaking Attacks

An Attacker could simply add small, random tweaks in order to destroy the message.

7) Structural Attack

Steganographic algorithms generally leave a characteristic structure to the data. The organization of the information document is distinctive when data is implanted into it. The assailant can without much of a stretch distinguish the nearness of the secret message by analyzing the factual profile of the bits. These progressions to the information record for the most part fall into effortlessly discernible example that gives a sign of a hidden message.

8) Visual Attack

The visual assault is a stego-just assault that strips away piece of the question in way that takes into consideration a human to look for visual peculiarities. The most well-known assault is to show the minimum huge piece of a protest; Digital types of gear, for example, cameras are not impeccable and regularly leave echoes at all critical bits. These totally arbitrary commotions demonstrate the presence of a concealed message. The normal ear can get unobtrusive contrast in sound. Be that as it may, this is moderate and expensive attack.