GSM A5 Cracking topic is started to be public material since The Hacker Choice disclosed their research. Many open source materials related to GSM are released to the public on Osmocomm. Now, tool called Kraken is freely distributed on internet to crack GSM A5.

I am pleased to announce the first release of a A5/1 cracker capable
using the full Berlin set of rainbow tables for lookups. I have named
this beast Kraken, after a Norse mythological creature capable of eating
many things for breakfast. Kraken feeds of an exclusive diet of A5/1
encrypted data.

Currently only a bare bone functionality is present, but the UI will be
improved, with the specific goal of providing an easy to use tool for
cracking GSM intercepts. But setting up this Leviathan can a bit
cumbersome, so I will give a short howto here:

Prerequisites:

* Linux machine, multicore min 3GB RAM
* 1.7 - 2TB of HD partitions without filsystem ( ex Samsung spinpoint F3s,
  with 4k aligned start of partition )
* The Berlin A5/1 Rainbow table set
* GPU support will be added for ATI Radeon HD

Setup:

Find out how many tables you want on each partition, (usually roughly
equal on each) and make the initial configuration file. An example
configuration folder can be found in tinkering/A5Util/indexes. This
folder should contain a tables.conf file. The example files shows a
setup of 4 disk having 10 tables each. The index files for the various
tables will be added to the index folder as they are written to disk.
The first section of the config file needs to be set up with the list of
available partitions, and the number of tables that each partition
should hold. A single table needs 42GB of space. (Do NOT change the
order of this section)

For safety reasons it is best not to build the tables running as root.
The you will then have to make your table partitions user accessible.
Add a file such as 10-disk.rules in /etc/udev/rules.d with one line for
each partition:

KERNEL=="sda1", OWNER="frank"

Then manually change the ownership of the device nodes with chown. Take
care when doing this, as you do not want to nuke any of your system
partitions.

Add tables to your disk array:

First build and make a symlink from your index folder to the
TableConvert tool. It is assumed that the Berlin tables are available in
either SSD or index free delta format. The python script Behemoth.py
will recursively search for tables, and add them to the disk array and
configuration file as needed. (Duplicates will not be added) - This
operation(s) will take some hours to complete, but when done you should
end up with a tables.conf file listing ~40 tables, their advance
parameter (id), which device they reside on, and a block offset into the
device.

Build and fire up Kraken:

./kraken path_to_index_folder

Currently it will only load up all tables, and crack TDMA burst 998 for
the challenge data. This takes 1.5 minutes on a 4 core Phenom II using
only CPU power, and the output should look like:

Cracking
0011011100110000000010000011000110001001101101100110110100111100011010
10100100101111111010111100000110101001101011
Found de6bb5e60617f95c @ 12
Found 6fb7905579e28bfc @ 23

A more interactive UI with appropriate data formats (representations)
will be added for easy interfacing with airprobe. Optional GPU support
will also be added for faster cracking time.

cheers,
Frank

Source : http://lists.lists.reflextor.com/pipermail/a51/2010-July/000683.html

Well the article form http://computerworld.com is really nice to read!

The GSM technology used by the majority of the world’s mobile phones will get some scrutiny at next week’s Black Hat security conference, and what the security researchers there have to say isn’t pretty.

On Friday, an open source effort to develop GSM-cracking software released software that cracks the A5/1 encryption algorithm used by some GSM networks. Called Kraken, this software uses new, very efficient, encryption cracking tables that allow it to break A5/1 encryption much faster than before.

The software is key step toward eavesdropping on mobile phone conversations over GSM networks. Since GSM networks are the backbone of 3G, they also provide attackers with an avenue into the new generation of handsets.

In December, the group released a set of encryption tables designed to speed up the arduous process of breaking A5/1 encryption, but the software component was incomplete. Now the software is done, and the tables are much more efficient than they were seven months ago. “The speed of how fast you could crack a call is probably orders of magnitude better than anything previously,” said Frank Stevenson, a developer with the A5/1 Security Project. “We know we can do it in minutes; the question is, can we do it in seconds?”

As the software becomes more polished it will make GSM call eavesdropping practical. “Our attack is so easy to carry out, and the cost of attack is lowered so significantly, that there is now a real danger of widespread intercepting of calls,” Stevenson said.

Stevenson and his co-developers haven’t put together all the components someone would need to listen in on a call — that would be illegal in some countries. Someone must still develop the radio listening equipment needed to gain access to the GSM signal, but that type of technology is within reach. Stevenson believes that this could be done using an inexpensive mobile phone and a modified version of open-source software called OsmocomBB. Hackers could also use a more-expensive Universal Software Radio Peripheral (USRP) device in conjunction with another program, called Airprobe.

A5/1 Security Project leader Karsten Nohl will discuss the hardware and software setup for his project’s GSM cracking tools at next week’s conference.

Last year there were about 3.5 billion GSM phones in use, according to data from the GSM Association. Not all of these phones are on networks that use A5/1 encryption — some use the more-secure A5/3 algorithm; others use no encryption — but a sizeable percentage are.

In the U.S., both AT&T and T-Mobile operate GSM networks.

The trade group that represents GSM network operators and equipment manufacturers, the GSM Association, has said in the past that A5/1 cracking efforts such as this are interesting, but attacks are extremely difficult to pull off in the real world. Intercepting mobile phone calls is illegal in many countries, including the U.S. The GSM Association did not respond to messages seeking comment for this story.

Project developers say the point of their work is to show how easy it really would be to crack A/51 — something they say that grey market commercial products are already doing. According to Stevenson many of these security problems are solved in next-generation mobile network technologies such as 3G and LTE (Long Term Evolution).

However, even 3G phones can be compromised because they can roll back to GSM mode when a 3G network is not available. “You can choose to operate in 3G mode only, but then you will have very limited coverage,” Stevenson said. “GSM has become the Achilles Heel of 3G security.”

Meanwhile, another Black Hat presenter, Chris Paget plans to demonstrate a completely different way to intercept GSM calls. He’s setting up a fake cellular tower that masquerades as a legitimate GSM network.

According to Paget, using open-source tools and a US$1,500 USRP radio, he can assemble his fake tower, called an IMSI (International Mobile Subscriber Identity) catcher. In a controlled experiment, he’s going to set one up at Black Hat and invite audience members to connect their mobile phones. Once a phone has connected, Paget’s tower tells it to drop encryption, giving him a way of listening in on calls.

“I think there’s been too much focus on the cryptographic weaknesses in GSM,” he said. “People need to recognize that the cryptographic weaknesses are not the worst weaknesses in GSM. “

Tags: A5, Cracking, Exploitation, GSM
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