Steganography and its techniques

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Steganography

What is Steganography?

Steganography comes from the Greek words: STEGANOS – covered and GRAPHIA– writing.

Steganography is the art and science of writing hidden messages in such a way that no one, apart from the sender and intended recipient, suspects the existence of the message.

The point of steganography is:If attacker knows there is a message, even if encrypted, he will try to decrypt it. However, if there is no visible message, then the message is safe!

Example:

Since everyone can read, encoding textin neutral sentences is doubtfully effective

Since Everyone Can Read, Encoding TextIn Neutral Sentences Is Doubtfully Effective

‘Secret inside’

History of Steganography

The first recorded uses of steganography can be traced back to 440 BC when Herotodus mentions two examples of steganography in his Histories.

Wax tablets were in common use then as reusable writing surfaces, sometimes used for shorthand.

Ancient example is that of histories, who shaved the head of his most trusted slave and tattooed a message on it. After his hair had grown the message was hidden. The purpose was to instigate a revolt against the Persians.

Special “inks” were important stenographic tools even during Second World War.

History of Steganography

Ancient Chinese wrote messages on fine silk, which was then crunched into a tiny ball and covered in wax. The messenger then swallowed the ball of wax.

During Second World War a technique was developed to shrink photographically a page of text into a dot less than one millimeter in diameter, and then hide this microdot in an apparently innocuous letter. (The first microdot has been spotted by FBI in 1941.)

In October 2001, the New York Times published an article claiming that al-Qaeda had used steganography to encode messages into images, and then transported these via e-mail and possibly via USENET to prepare and execute the September 11, 2001 terrorist attack.

Physical Techniques

Hidden messages within wax tablets Hidden messages on messenger's body Hidden messages on paper written in secret inks Messages written in Morse code on knitting yarn and

then knitted into a piece of clothing worn by a courier Messages written on envelopes in the area covered by 

postage stamps.

Digital Techniques

Concealing messages within the lowest bits of noisy images or sound files.

Pictures embedded in video material (optionally played at slower or faster speed).

Modifying the echo of a sound file (Echo Steganography)

Including data in ignored sections of a file, such as after the logical end of the carrier file.

Steganography V/S CryptographySteganography Cryptography

Unknown message passing Known message passing

Steganography prevents discovery of the very existence of

communication

Encryption prevents an unauthorized party from

discovering the contents of a communication

Little known technology Common technology

Technology still being develop for certain formats

Most of algorithm known by all

Once detected message is knownStrong current algorithm are

resistant to attacks ,larger expensive computing power is

required for crackingSteganography does not alter the structure of the secret message

Cryptography alter the structure of the secret message

Best Of Both Worlds!

Terms related to Steganography

Carrier or Cover File - A Original message or a file in which hidden information will be stored inside of it .

Stego-Medium - The medium in which the information is hidden.

Embedded or Payload - The information which is to be hidden or concealed.

Steganalysis - The process of detecting hidden information inside a file.

Different Types of Steganography

Text SteganographyImage SteganographyAudio SteganographyMessage in TCP/IP packets

Text Steganography

Text steganography can be applied in the digital makeup format such as PDF, digital watermark or information hiding

It is more difficult to realize the information hiding based on text. The simplest method of information hiding is to select the cover first, adopt given rules to add the phraseological or spelling mistakes, or replace with synonymy words.

Example:

An example of a message containing cipher text by German Spy in World War II:

“Apparently neutral's protest is thoroughly discounted And ignored. Isman hard hit. Blockade issue affects .Pretext for embargo on by products, ejecting suets and Vegetable oils. ”  

Taking the second letter in each word the following message emerges:

Pershing sails from NY June 1.

Other Methods:

White Steg Inter Sentence spacing Inter Word spacing

SMS texting – abbreviated and full formSyntactic method - punctuationsMisspell method

Image Steganography

Least Significant Bit Method

Least significant bit (LSB) insertion is a common, simple approach to embedding information in a cover image

The least significant bit (in other words, the 8th bit) of some or all of the bytes inside an image is changed to a bit of the secret message

When using a 24-bit image, a bit of each of the red, green and blue color components can be used, since they are each represented by a byte. In other words, one can store 3 bits in each pixel. An 800 × 600 pixel image, can thus store a total amount of 1,440,000 bits or 180,000 bytes of embedded data

In its simplest form, LSB makes use of BMP images, since they use lossless compression

Example

A grid for 3 pixels of a 24-bit image can be as follows:(00101101 00011100 11011100)(10100110 11000100 00001100)(11010010 10101101 01100011)

When the number 200, which binary representation is 11001000, is embedded into the least significant bits of this part of the image, the resulting grid is as follows:

(00101101 00011101 11011100)(10100110 11000101 00001100)(11010010 10101100 01100011)

Original Image Modified Image

The difference is invisible to naked eye!

Pixel Indicator

Applications

Storing passwords and/or other confidential informationCovert communication of sensitive dataSpeculated uses in terrorist activitiesBeing widely used to hide and/or transfer illegal content

SPS – Static Parsing Steganography

The sender and the receiver agree on a cover image.The protocol does not modify the cover image.Rather determines the bits of the secret message that

match the ones in the cover image and stores their different locations (i.e. in the cover image) in a vector.

Then it is sent to the recipient.

Example

Masking & Filtering

Masks secret data over the original data by changing the luminance of particular areas

During masking, it embed the message within significant bits of the cover image

Not susceptible to lossy techniques because image manipulation does not affect the secret message

Audio Steganography

Embedding secret messages into digital sound is known as Audio Steganography.

Audio Steganography methods can embed messages in WAV, AU, and even MP3 sound files.

The properties of the Human Auditory System (HAS) are exploited in the process of audio Steganography

To embed data secretly onto digital audio file there are few techniques :

LSB Coding Phase Coding Parity Coding Spread Spectrum

Let us see how these techniques are used…

Audio Steganography

Flowchart:

Phase Coding

The phase coding method works by substituting the phase of an initial audio segment with a reference phase that represents the data. The procedure are as follows :Original sound sequence is broken into a series of N short

segments.A discrete Fourier transform(DFT) is applied to each

segment to create a matrix of the phase and magnitude.Phase difference between each adjacent segment is

calculated.

Phase shifts between adjacent segments are easily detectable. So secret information is inserted only in the phase vector of 1st

signal segment as :Using new phase of the 1st segment a new phase matrix is

created and the original phase differences.Sound signal is reconstructed by applying inverse DFT

using new phase matrix & original magnitude matrix & concatenating sound segments back together.

The receiver must know the segment length to extract the secret information from the sound file.

Then receiver can use the DFT to get the phases and extract the secret information

Parity Coding

One of the robust audio stenographic technique.Instead of breaking a signal into individual samples,

this method breaks a signal into separate samples Encode each bit of the secret message in sample

region’s parity bitIf the parity bit of a selected region does not match the

secret bit to be encoded the process inverts the LSB of one of the samples in the region.

Thus, the sender has more of a choice in encoding the secret bit

Spread Spectrum

The basic spread spectrum (SS) method attempts to spread secret information across the frequency spectrum of the audio signal.

This is similar to a system which uses an implementation of the LSB that spreads the message bits randomly over the entire sound file.

Unlike LSB coding, the SS method spreads the secret information over the frequency spectrum of the sound file using a code which is independent of the actual signal

As a result, the final signal occupies a bandwidth which is more than what is actually required for transmission.

Steganography in TCP / IP Packets

Protocols in the OSI network model have vulnerabilities that can be used to hide information.

The TCP packet header has six unused(reserved) bits and the IP packet header has two reserved bits.

They provide an excellent covert communication channel if unchecked.

Tool Demo

Future Scope of Steganography

Steganography, though is still a fairly new idea. There are constant advancements in the computer field, suggesting advancements in the field of steganography as well. It is likely that there will soon be more efficient and more advanced techniques for Steganalysis. A hopeful advancement is the improved sensitivity to small messages. Knowing how difficult it is to detect the presence of a fairly large text file within an image, imagine how difficult it is to detect even one or two sentences embedded in an image! It is like finding a microscopic needle in the ultimate haystack.

What is scary is that such a small file of only one or two sentences may be all that is needed to commence a terrorist attack. In the future, it is hoped that the technique of Steganalysis will advance such that it will become much easier to detect even small messages within an image.

Thank You!