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LSB Method (Part 2) LSB method

In brief, the LSB method is characterized by the following:

1. The information is hidden in the least significant bits.
2. The method is robust, since if the watermarked image is distorted information is lost. An analysis
3. visually LSB plane, one can see that "something strange" (visual assault), which can cause an attacker to distort the image to remove the information.

As the third point, when you mark an image with the LSB method can be noticed at a glance the distortion generated by modifying the least significant bits as shown in the previous entry. In that entry newspaper hid a message in reality it is very unlikely to have it. What we will do then is to hide text in the image. Each letter of the text will be converted to ASCII value (8 bits), so the message will hide a series of 8-bit numbers. The message is the famous hide poetry of Mario Benedetti teacher (who recently passed away) called " not save yourself." Then write an extract from the poem:

Never
salves Mario Benedetti


not stay still on the roadside does not freeze the joy

not want
reluctantly
not save yourself now or ever

not save yourself ...

The image marked with the poetry and the LSB plane is shown below:

Lena marked with a poem by Benedetti

As you can see a pattern of vertical lines due to the ASCII encoding we use, since many letters share certain bits, like the lowercase letters that belong to a small range of the ASCII encoding. Poetry hidden in the image consists of 762 Bytes. If poetry hide 5 times the image can better see the pattern of vertical lines generated:

vertical pattern generated at the LSB to hide text

To avoid this pattern generated by hiding the text in the image can hide a random mark at the LSB. Before proceeding with this amendment they will list the main changes you can make the LSB method.

The main changes are LSB Method: Hide

1. random information in the LSB plane to avoid a visual assault.
information
2. Hide image edges to avoid homogeneous zones to avoid visual attacks. Using more levels
3. LSB for hide information. Use
4. LSB method to detect changes made in the image. Using the method
5. LSB as a reversible method to extract the original image of the brand.

The first modification is to randomly hide bits of the message in the image. The path we will take the brand random mess. The way to do it after taking the bitstream of the mark will proceed to scramble it using a key. This key will be necessary to rearrange the mark after removal of the marked image. Then observe the marked image and the LSB plane of the same. To do the same poetry hide Benedetti described above.

Lena marked with a random message

We can realize a visual attack have no effect if the mark randomly hide because we can not take in some pattern or something that looks strange in LSB plane. The following image shows the significant difference of not using and using a random mark.

Comparison of LSB planes marked using original and random marks

Another way to make this amendment is to randomly distribute the brand in the entire LSB plane.

The first amendment prevents a visual attack, but there a type of attack called statistical chi-square that can detect the presence of the mark in the marked image as long as the mark is hidden in a random .

In the next post will describe the Chi square test, then we will continue with the other four remaining LSB modification method.

Greetings to all.

PD. The source code (in Matlab) of the methods discussed in this post are listed below:
1. LSB Method hiding a message in an image bmp paper (described in the previous post).
2. LSB Method hiding text in a bmp image.
3. LSB Method hiding text in a bmp image randomly.

Blogalaxia Tags: LSB Steganography Method Attack visual images

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The most basic way to hide information in images is by using the method LSB (Least Significant Bit English, English bit less significant). Unfortunately not know the reference of the first work which mentions the use of this method, if any of you know please help me to know.

This method involves replacing the least significant bits each pixel with the bits of information to hide.

As the best way to learn is by example, then we see this method in action. Take

carrier medium Lena image, the message will hide 2048 bits in length and will follow the following pattern:

Message = 11111111 00000000 11111111 00000000 ...

Lena image, used to hide the message

As mentioned in the entry some images, the images are formed by a depth of color, is the case Lena image is an image of 8 bits. That is, each pixel is represented with 8 bits, which causes the image is 256 colors (in this case is in gray scale) ranging from black (0 in decimal or in binary 00000000 ) to white (255 in decimal or in binary 11111111 ).

The least significant bit (lsb in lower case or to refer to the least significant bit and not the method for hiding information) determines the parity of a number. The lsb is also known as the rightmost bit . Against part or most significant bit msb represents the most bit left. For example in the following image shows the binary representation of decimal number 211 , the lsb is marked with orange and purple color lsb. The msb represents a decimal value of 128 lsb and a decimal value of 1 .

Binary representation of decimal number 211 , the lsb is marked with orange

The plane lsb is 1-bit binary image formed by all the lsb of the image. The following image depicts the LSB plane of the image of Lena.

lsb of Plano Lena image

Now for the other planes binary image of Lena.

Plans binary image of Lena

LSB method is to modify the LSB plane of the image carrier with the brand to hide. Thus, if we replace lsb bits of the plane row by row with the brand mentioned above (the pattern of eight zeros and eight ones) resulting lsb level will appear as shown in the picture below.

lsb Plano marked

The watermarked image, ie the image with the modified lsb plane is shown below.

marked Lena image using the LSB method

is important to note that if we see the two images can not perceive Jutas which is marked and what is the original, since it only changed the value of the pixels in a unit and this happens at the worst. The following image shows the original Lena image, the watermarked image and finally the absolute difference of the two images. In this last image the white pixels represent the pixels that changed in magnitude to be marked.

difference between the original Lena image and marked

These changes made using the LSB method are imperceptible to the human eye, however if the level is plotted lsb can easily notice that "something strange in the picture" and not for the fact that we have used a clearly visible mark above. You might think that the plane has a random nature lsb, ie not have a pattern like the other planes (ie the bit planes 4,5,6,7 and 8) but the reality is different, the plane if you have lsb a pattern that depends on the image, but at first glance not feel it. For example the following figure shows a flat image and lsb. Here you may notice a pattern to the naked eye at the lsb.

Pattern en el plano lsb de la imagen Bird

Para evitar que la marca sea detectada a simple vista (esto se considera un ataque visual, como se mencionó en la entrada clasificaciones de las marcas de agua ), muchos diseñadores no la esconden linealmente como lo hicimos en el ejemplo descrito, sino la esconden en posiciones dadas por un generador de números pseudoaleatorios, así la esparcen en toda la imagen incrementando la indetectibilidad.

En la siguiente entrada analizaremos más a fondo este método LSB y de igual forma mostraremos unas modificaciones del mismo. Por ejemplo, la modificación para ocultar una imagen dentro de otra, la modificación para detectar cambios hechos en marked image (integrity) and can be modified to recover the original image of the watermarked image (reversible method).

Be well and we are in contact ...

PD. The source code (in Matlab) of the method explained in this entry is listed below:
1. LSB Method hiding a message in an image bmp newspaper.


LSB Steganography Method lsb Plano Images

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auto_install FFmpeg on Mac OS X

This entry is a break from the previous post and that I will later (the explanation of the LSB method to hide information in pictures) ... The posting because I had this information written As I have not written anything, I did not leave without reading a while lol ...

Thus, I will describe the installation of FFmpeg in Mac OS X and the steps required to do so and additional resources used.

Importantly FFmpeg is a collection of free software that can record, convert and makes streaming audio and video (used in Windows, Linux, Mac OS or other operating systems) ... Mind you, we utlized a FFmpeg libraries to manipulate our videos from programming in C (libavcodec and libavformat). For more information about FFmpeg can give click here . Other library

free and open-source used for handling video (in Java) is Xuggle ... This library is brand new package for the released later this year. Note that Xuggle uses FFmpeg to do such work.

First, instalarmos FFmpeg on Mac OS X 10.5.6 on an Intel MacBook Pro The source of information in this post is on this page: Installing and using FFmpeg on Mac OS X .

The intention to do later is to use the FFmpeg libraries to manipulate each of the frames of a video (hide details) and return to the same.To this video, you need to install are the tools development of apple. Mainly install XCode 3.1 or higher, comes on the DVD included with the Mac or can be downloaded from the Development Tools

apple then install FFmpeg and accessories.

Prerequisites: LAME

Libraries to handle MP3, useful when handling flv videos. FFmpeg does not include an MP3 encoder, because it will use LAME. The installation steps down the source codes are:

1. Create a working directory home :

mkdir ~ / lame
cd ~ / lame

2. Download the sources from SourceForge . The file has a name like lame-398-2.tar.gz or something similar. Keep them in the new directory created (step 1).

3. Decompress the source, using this command (you have to be inside the folder lame):

tar xvzf lame-398-2.tar.gz

4. Decompression creates a new folder : lame-398-2 in which you have to go and continue with the three typical installation command. To do so, write these commands

cd lame-
398-2. / Configure

make sudo make install

Each command takes about a minute to complete. We must be alert for errors that are generated, but LAME is usually error-free installation.

Installing FFmpeg on Mac OS X 10.5.6

will install the latest version of FFmpeg. (Versions 3.1 or higher are included Xcode subversion , no need to install Fink ). The installation steps are:

1. Create a working directory

mkdir ~ / ffmpeg
cd ~ / ffmpeg

2. Download the latest version of FFmpeg svn path (in our case the data were reviewed 17,451).

svn checkout svn: / / svn.ffmpeg.org / ffmpeg / trunk ffmpeg cd ffmpeg


3. Then configure and make

. / Configure - enable-libmp3lame - enable-shared - disable-mmx

make sudo make install

parameter - disable-mmx not Power PC is required. If left on an Intel Mac, you will probably get some compile errors, but this will provide speed. Congratulations

have FFmpeg installed in our Mac With this you can manipulate audio and video (see tutorial ) and better yet we can use the libraries do.

To verify correct installation simply open the Cosola and write

ffmpeg

The output should look like this

FFmpeg version SVN-r17451, Copyright (c) 2000-2009 Fabrice Bellard, et al.
configuration: - enable-libmp3lame - enable-shared - disable-mmx libavutil 49.14
. 0 / 49.14.
0 libavcodec 52.16. 0 / 52.16.
0 libavformat 52.29. 1 / 52.29. 1
libavdevice 52. 1. 0 / 52. 1. 0
built on February 19, 2009 2:52:53, gcc: 4.0.1 (Apple Inc. build 5484)
At least one output file
Must Be Specified

A command to view information about a video called Video.avi is:

ffmpeg-i video.avi

After this roll will continue with management and FFmpeg libraries,
Greetings to all.


FFmpeg LAME Xuggle Mac OS X