August 2010 | Linux Poison

How to block flash videos using Squid proxy Server

A popular request is to block certain content types from being served to clients. Squid currently can not do "content inspection" to decide on the file type based on the contents, but it is able to block HTTP replies based on the servers' content MIME Type reply.

The MIME Type reply is generally set correctly so browsers are able to pass the reply to the correct module (image, text, html, flash, music, mpeg, etc.)

One popular example is to block flash video, used by sites such as Youtube.
The MIME type for such content is "video/x-flv". Creating an ACL to block this is easy.

First, create an ACL which matches the MIME type in question:

acl deny_rep_mime_flashvideo rep_mime_type video/x-flv

Then create a HTTP Reply ACL which denies any replies with that MIME type:

http_reply_access deny deny_rep_mime_flashvideo

This has been verified to block Youtube flash video content.

If the content is blocked the following similar line will be seen in access.log:

1282485682.146 903 127.0.0.1 TCP_DENIED_REPLY/403 3143 GET http://tc.v15.cache3.c.youtube.com/videoplayback? - DIRECT/208.117.252.163 text/html

And on browser, you can see ...

Enable Surround Sound system (5:1) in Ubuntu

To enable 5:1 surround sound system for your Ubuntu, go to terminal and open the file (/etc/pulse/daemon.conf) using your editor and change the line:

$ sudo gedit /etc/pulse/daemon.conf
; default-sample-channels = 2

to say

default-sample-channels = 6

After you reboot, test your sound using: speaker-test -Dplug:surround51 -c6 -l1 -twav

How to Hide data (Steganography) into image file - OutGuess

OutGuess is a universal steganographic tool that allows the insertion of hidden information into the redundant bits of data sources. The nature of the data source is irrelevant to the core of OutGuess. The program relies on data specific handlers that will extract redundant bits and write them back after modification. In this version the PNM and JPEG image formats are supported.

This process will allow us to store information of any kind within an image. This can be useful if you intend to send confidential information (such as a text document or a spreadsheet) to a person and do not want such information to be intercepted by someone else (such as the mail provider, a spy, police, etc. ..) We will use the technique of steganography to hide information within the image.

OutGuess Installation:
Ubuntu user can install OutGuess using Synaptic package manager or can install using command:
sudo apt-get install outguess

Data Embedding using OutGues:
Now here is how you do it: you need a text file (in this example we call it "hidden.txt" ) and a picture ( we call it "input.jpg" ) after that you issue the following command to hide your data ("hidden.txt") into the image file.

$ outguess -k "my_passwd" -d hidden.txt input.jpg out.jpg
Reading input.jpg....
JPEG compression quality set to 75
Extracting usable bits: 43283 bits
Correctable message size: 24627 bits, 56.90%
Encoded 'hidden.txt': 1128 bits, 141 bytes
Finding best embedding...
   0: 587(50.6%)[52.0%], bias 68(0.12), saved: -2, total: 1.36%
   15: 550(47.4%)[48.8%], bias 73(0.13), saved: 1, total: 1.27%
   41: 585(50.4%)[51.9%], bias 32(0.05), saved: -2, total: 1.35%
  198: 540(46.6%)[47.9%], bias 50(0.09), saved: 3, total: 1.25%
198, 590: Embedding data: 1128 in 43283
Bits embedded: 1160, changed: 540(46.6%)[47.9%], bias: 50, tot: 43059, skip: 41899
Foiling statistics: corrections: 174, failed: 187, offset: 158.255556 +- 316.069419
Total bits changed: 590 (change 540 + bias 50)
Storing bitmap into data...
Writing out.jpg....
$

Data Retrieval
You can retrieve data from an image in the following way:
$ outguess -k "my_passwd" -r out.jpg hidden.txt
Reading out.jpg....
Extracting usable bits: 43283 bits
Steg retrieve: seed: 198, len: 141

Script to add multimedia support to Ubuntu

Ubuntu Multimedia Support Script will add Medibuntu repository and clipgrab ppa and will install the complete multimedia support.

It will install:
- Java Support
- Flash Player Plugin
- Gstreamer Codecs
- w32codecs
- Non-free extra codecs

Instructions:
NOTE: Before continuing, please make sure that all default repositories (exspecially partners' ones) and updates are enabled.

1) Download the script - here
2) Right-click the script you will use, go to proprieties and to the Permissions tab. Select Allow executing as program.Close the window.
3) Now left-click on the script and run it in terminal.