CRACKING
WEP WITH WINDOWS XP PRO
There is a Video Counterpart to this
which is in the format of me describing what I am doing and how to
carry out all the actions in this paper from start to finish. It will
be available as soon as I can secure my web site adequately and will
only ever be available to registered TAZ members. This paper should be
considered the pre-reading for the video tutorial.
This is part one in a two part
paper on Cracking WEP with Windows XP. This first part covers sniffing
wireless traffic and obtaining the WEP key. Part Two will cover
associating with a Wireless AP, spoofing your MAC address, trying to
log on administratively to the AP and further things you can carry out
on the WLAN once authenticated successfully.
What is WEP:
Wired Equivalent Privacy (WEP) is often mistakenly thought of as a
protocol designed to 100% protect wireless traffic, when this is not
the case.
As its name suggests it was designed to give wireless traffic the same
level of protection as a wired LAN, which when you think about it is a
very hard thing to set out to do.
LAN’s are inherently more secure than Wireless LAN’s (WLAN) due to
physical and geographical constraints. For an attacker to sniff data on
a LAN they must have physical access to it – which is obviously easier
to prevent than to prevent access to traffic on a WLAN.
WEP works at the lower layers of the OSI model, layers One and Two to
be exact, so it therefore does not provide total end to end security
for the data transmission.
WEP can provide a level of security between a Wireless Client and an
Access Point or between two wireless clients.
WEP Standards:
WEP is commonly implemented as a 64 bit or 128 bit encryption. These
encryption strengths can sometimes be referred to as 40 bit or 104 bit
due to the fact that each data packet is encrypted with an RC4 cipher
stream which gets generated by an RC4 key. This RC4 key for say a 64
but WEP implementation is composed of a 40 bit WEP key and a 24 bit
Initialization Vector (IV) – hence the 64 bit RC4 key, however the
actual WEP part of it is only 40 bits long, the IV taking up the other
24 bits, which is why a 64 bit WEP key is sometime referred to as a 40
bit WEP key.
This resultant cipher is ‘XOR’d’ with the plain text data to encrypt
the whole packet. To decrypt the packet the WEP key is used to generate
an identical ‘key stream’ at the other end to decrypt the whole packet
but more about this later on, I will also go over the IV’s in more
detail later on as well.
Failures of WEP:
We have heard everyone say WEP is easy to crack and should not be used,
can be cracked in 10 minutes etc but why is this?
Well in my opinion WEP is seriously flawed for the following reasons:
1) Initialization Vectors are reused with encrypted packets. As an IV
is only 24 bits long it is only a matter of time before it is reused.
Couple this with the fact you may have 50 + wireless clients using the
same WEP key and the chances of it being reused improve even further.
An IV is sent in clear along with the encrypted part of the packet. The
reuse of any encryption element is always a fundamental flaw to that
particular encryption and as an IV is sent in clear this further
exposes a significant weakness in WEP.
As more RC4 cipher steams are found and more IV’s are deciphered and
the closer we get to discovering the WEP key.
This is what forms the foundation of WEP cracking.
2) The algorithm used to encrypt a WEP ‘hash’ is not intended for
encryption purposes. The original purpose of the Cyclic Redundancy
Check (CRC-32) was to detect errors in transmission, not to encrypt
data.
3) The most significant flaw in my opinion is the mass use of the WEP
key. Everything using that particular AP will need the same WEP key
hence all the resultant traffic will be using the exact same WEP key as
well.
The one not so obvious side-affect of this is when it comes to
administering the network. If you have 60 wireless clients all using
the same WEP key, do you really want to go and periodially change them
all…..it is easier to leave it as it is. I am guilty of doing this on a
network I used to administer a few years ago as I am sure others are
who still use WEP.
Wireless Standards:
The Institute of Electrical and Electronic Engineers (IEEE) defined
specifications for wireless traffic back in 1997. The protocol they
came up with is the 802.11 standard.
Nowadays 802.11 has many different implementations for wireless
traffic. The most common ones are:
1) 802.11 – this specifies that the wireless traffic will use the
2.4GHz frequency band utilizing either Frequency Hoping Spread Spectrum
(FHSS) or Direct Sequence Spread Spectrum (DSSS). The FHSS is a
protocol whereby the traffic ‘hops’ to pre-defined frequencies and is
commonly used to reduce the effects of noise or interference in the
transmission. DSSS is also a protocol used to reduce noise interference
by combining the signal with a higher data rate bit sequence (commonly
called a chipping code) which separates the data up in to a logical
sequence and attaches a form of CRC to the packet before transmitting.
2) 802.11a – this provides data transmission in the 5GHz band at a rate
of anything up to 54Mbps. Unlike the original 802.11 specification this
uses Orthogonal Frequency Division Multiplexing (OFDM) to encode the
traffic instead of FHSS or DSSS. OFDM is a method of transmitting
digital data by splitting it up in to smaller ‘chunks’ and transmitting
them at the same time but on different frequencies, which is why the
data transfer rate is quite good.
3) 802.11b – came along in 1999 with the intention of allowing wireless
functionality to be similar to that provided by Ethernet. It transmits
data in the 2.4GHz band at 11Mbps using DSSS only. Is sometimes called
Wi-Fi.
4) 802.11g – this works in the 2.4 GHz band at a rate of 20Mbps or more
and came along in 2003. It uses OFDM like 802.11a and transmits data in
a very similar way. However unlike 802.11a it is backward compatible
with 802.11b.
A point worth noting here is if you have an 802.11b Wireless Adaptor
you will not be able to receive 802.11g traffic. If you do want to get
in to WEP cracking it is well worth your while investing in a dual band
card. I will talk about Wireless Adaptors more later on.
How do we crack WEP:
Well cracking WEP is fairly easy to understand if you have followed
what I explained above. We briefly touched on IV’s and WEP encryption
and how they tie in together. To put it very simply, if you can
decipher the IV algorithm you can decrypt or extract the WEP key.
As I stated before WEP very kindly transmits the IV in clear, so if we
can run a mathematical equation against it we can find and decipher the
RC4 stream that encrypted the whole packet in the first place.
The WEP ‘key’ is the missing value [key] from this mathematical
equation. Remember the AP or the client has this key to use when
decrypting the packet and is what we must find by running a complicated
algorithm against the encrypted packet.
If you think about it like this it may become clearer:
You have an algorithm that is produced by concatenating a randomly
generated 24 bit IV with your WEP Key – You also have an RC4 Key stream
- the two are then ‘hashed’ together to encrypt the packet.
The IV is the hub of the whole process as this is they only thing that
has used your WEP key. If we run a statistical anyalisis against the IV
to try and decrypt the packet, we can find the key used at the begining
of the process.
When you try to decrypt them, every time you crack a piece of the
algorithm the corresponding plain text part of the packet is revealed,
once the whole packet is decrypted you know the algorithm used to
encrypt that particular packet – A crude way of describing it but as
simple as I can make it.
Any attacker can passively collect encrypted data, after a while due to
the limitations explained earlier; two IV’s that are the same will be
collected. If two packets with the same IV are XOR’d, an XOR of the
plain text data can be revealed. This XOR can then be used to infer
data about the contents of the data packets.
The more identical IV’s collected the more plain text data can be
revealed. Once all the plain text of a data packet is known, it will
also been known for all data packets using the same IV.
So before any transmission occurs WEP combines the keystream with the
payload using an XOR process, which produces ciphertext (data that has
been encrypted). WEP includes the IV in clear in the first few bytes of
the frame. The receiving AP / Client uses this IV along with the shared
secret key (Your WEP Key) to decrypt the payload of the frame.
XOR is a mathematical algorithm which I am not even going to attempt to
explain. This site explains it very well though:
http://mathworld.wolfram.com/XOR.html
So in short – the more identical IV’s we can get the more plain text
data we can reveal and the closer we get to obtaining the key used to
encrypt the data in the first place.
As it is not pre-determined when we are going to receive identical IV’s
it is impossible to say how many IV’s need to be collected but more
about that later.
Software Used:
For this attack I am going to use aircrack-ng for Windows which can be
obtained from here:
http://tinyshell.be/aircrackng/wiki/index.php?title=Aircrack-ng
Whilst here download cygwin1.dll and paste it in to the same folder as
Aircrack-ng. There is a copy of cygwin1.dll included already but the
one available from the tinyshell site is a later version of it.
The peek.dll and peek5.sys files also need to be in the same directory
as aircrack. They are available here:
If you download Winaircrack - which is a GUI version of what I cover in
this paper - copy the peek.dll and peek5.sys files across to where you
have aircrack stored. You will get a peek driver not found message if
you dont do this.
Once it has downloaded you have to option of pasting the directory path
of it in to your Command Prompt path so you can start the application
straight from the command line without having to ‘CD’ to the correct
directory.
For example I copied this in to my path: C:\Documents and
Settings\Nokia\Desktop\aircrack-ng-0.3-win\aircrack-ng-0.3-win\bin
In the bin folder is airodump and aircrack-ng – so now I can just type
airodump straight in to the command prompt to run the application.
To add something to your path:
Right click My Computer > Properties > Advanced > Environment
Variables > Under System Variables highlight PATH > Edit >
enter the directory path using a ; to separate it from any existing
entries.
You also need to go to Wild Packets to pick up a new driver for your
card. http://www.wildpackets.com/
I have found that the most common cause of stress when trying to crack
WEP is incompatible hardware. The Airopeek driver from Wild Packets is
not compatible with all types of hardware. There is a list of supported
adaptors and the relevant driver you need to use on the web site.
For this crack I am using an Atheros based NETGEAR WAG511 DUAL BAND
adaptor which you can get from HERE for £35.99.
This card works with Whax, Auditor and BackTrack pretty much straight
out of the box. It is also a dual band so you don’t have to worry about
sniffing traffic on a ‘g’ WLAN when you have a ‘b’ wireless adaptor. It
is my preferred Wireless Adaptor and has not let me down yet.
Most cards that are Atheros based will have the Atheros logo on the
side of the box, use one of these if possible.
**Some people I know have confused the NETGEAR WG511 which does not
work, with the NETGEAR WG511T which does work so try not to fall in to
this trap**
Cards that I can 100% say to stay away from are ones that use the
PrisimGT chipset. Connexant cards are also a complete waste of time
(which I found out the hardway) so please do not even think about
buying one of these if you want to crack WEP.
See this list to check what chipset your card uses:
http://www.linux-wlan.org/docs/wlan_adapters.html.gz
So you should now have:
Aircrack-ng
Cygwin1.dll – in the same directory as Aircrack
Peek.dll and Peek5.sys in the same directory as Aircrack
Relevant Drivers from Wild Packets for your Adaptor
Added aircrack-ng to your PATH
Got an Adaptor that works with all of the above!
So what’s next?
Now we need to install the driver you have downloaded.
**Warning – the next procedure will overwrite your existing Windows
driver, so make sure you have the disc or a backup of it before
carrying on.**
The peek driver will not let you use your Wireless Adaptor in the
conventional way. You won’t be able to associate to an AP with it or
browse the internet etc.
99% of Windows drivers a designed to make your Wireless Adaptor reject
any 802.11 traffic not destined for it. The Peek driver puts your
Adaptor in to a promiscuous mode to allow it to sniff all 802.11
traffic that is compatible with your adaptor.
To install the driver open up your Device Manager and right click on
your wireless adaptor > Update Driver > Install from a Specific
Location > Don’t Search, I will chose the driver to install >
Have Disk > Browse to where you have downloaded the driver >
Double Click.
Windows may display a prompt warning you that the driver is not
digitally signed, if ths happens click continue anyway.
Once the driver is installed we are ready to crack WEP.
**If you get an error message saying ‘The specified destination
contains no information about your device’, you have either downloaded
the wrong driver or more likely your Wireless Adaptor is not compatible
with what we need it to do.**
Cracking WEP:
Cracking WEP is by now means a skilful thing to do, as all the hard
work was done by Chris Devine who is the excellent coder of Aircrack,
all we need to do is collect the data and start the program. If you
have questions about Aircrack a good place to post them is on the
Netstumbler Linux Forums as I believe the author checks here quite
often. Alternatively you can email the author at devine [at] iie [dot]
cnam [dot] fr – whether he will reply or not I don’t know but I
wouldn’t have thought he will appreciate you emailing him with stupid
questions – use the forum for these!
Airodump
So open a command prompt and type Airodump – or if you have not added
it to your PATH you will need to CD to the right directory.
A new window opens now which will search for all installed wireless
adaptors, give it a numerical signature and display the following:
Code:
usage: airodump <nic
index> <nic type> <channel(s)> <output prefix>
[ivs only flag]
Known network adapters:
14 NETGEAR WG511T 54
Mbps Wireless PC Card
22 NETGEAR WAG511
802.11a/b/g Dual Band Wireless PC Card
Network interface index
number ->
Select the relevant ID for the card you want to use:
Code:
Network interface index
number -> 22
You are then prompted to enter the type of chipset of your card:
Code:
Interface types: 'o'
= HermesI/Realtek
'a' = Aironet/Atheros
Network interface type
(o/a) ->
We are using an Atheros card so we enter 'a':
Code:
Network interface type
(o/a) -> a
Then you are asked what channel you would like it to sniff traffic on:
Code:
Channel(s): 1 to 14, 0 =
all ->
The USA only uses up to channel 11 and Europe use up to channel 14.
Channel 11 in the UK is the most common one that wireless AP’s default
to however, so I normally start off with channel 11. If you want to
scan all channels use the 0 option.
We shall use channel 11:
Code:
Channel(s): 1 to 14, 0 =
all -> 11
Now you are asked what you would like to save your capture file as:
Code:
(note: if you specify the same output prefix, airodump will
resume the capture session by appending data to the existing capture
file)
Output filename
prefix ->
If you specify a file name that you have already used the resulting
data will be added to the file – which is an excellent feature if it
becomes apparent later on that you do not have enough IV’s as you won’t
have to start all over again!
Code:
Output filename
prefix ->WEP1
Now you are asked if you only want to save the IV’s or all packets that
are sniffed.
Code:
(note: to save space and only store the captured WEP IVs, press
y.The resulting capture file will only be useful for WEP cracking)
Only write WEP IVs
(y/n) ->
As we know to crack a WEP key we only need IV’s so we can select yes to
this question. The resultant file will be saved as an .IVS file.
Code:
Only write WEP IVs
(y/n) -> y
So now we have told it everything it needs to know, let’s see what
happens:
Code:
BSSID
PWR Beacons # Data CH MB
ENC ESSID
00:09:5B:FD:C6:52
10
3 6 11 54
OPN HOMEWIRELESS
00:30:F1:F5:A1:35
60 359 1234
11 54 WEP Stuart
BSSID
STATION
PWR Packets ESSID
00:09:5B:FD:C6:52
00:09:5B:B6:1D:2A
17 6 HOMEWIRELESS
00:30:F1:F5:A1:35
00:09:5B:84:A6:DF 87 1793
Stuart
This is the output from a successful Airodump start-up.
BSSID = The MAC address of the Wireless Access Point.
PWR = The strength of the signal being received
BEACONS = Every AP transmits around 10 beacons per second – these are
not encrypted and are useless to us from a WEP cracking point of view –
they basically say ‘ I’m an AP, come and associate with me’.
DATA = This is what we are interested in. DATA packets are our IV’s
that we need and what we are most interested in.
ENC = Encapsulation – WEP / WPA / OPEN etc – speaks for itself
ESSID = The name of the wireless network. This is not always
broadcasted by the AP but we will need it to associate with the AP
later on.
The second part lists any associated clients that are talking to the
AP. MAKE A NOTE OF THESE MAC ADDRESSES.
Some AP’s have MAC address filtering enabled. This is a table of MAC
addresses stored on the AP – when you try to associate with the AP if
MAC filtering is enabled the AP checks your MAC with the list of
allowed MAC’s to see if you can associate with it. If it is not in the
list, regardless of if you have the correct WEP key or not, you will
not be allowed to associate with the AP. You will also leave an entry
in the logs.
This is a very helpful feature of Airodump that informs us what we need
to spoof our MAC to when associating with the AP.
Original Tutorial
by nokia for TheTAZZone-TAZForum
Originally posted on June 23rd, 2006 here
Do not use, republish, in whole or in part, without the consent of
the Author. TheTAZZone policy is that Authors retain the rights to the
work they submit and/or post...we do not sell, publish, transmit, or
have the right to give permission for such...TheTAZZone merely retains
the right to use, retain, and publish submitted work within it's
Network.