1. WLAN What is WLAN? Physical vs. Wireless LAN
Wireless Local Area Network
Extension of a wired LAN
Uses high frequency radio waves (RF)
Speed: 2 MB/s to 54 Mb/s
Distance:100 feet to 15miles
Physical vs. Wireless LAN
Physical LAN has defined borders
Wireless is difficult to determine where access stops
Both are vulnerable to attacks

2. Standard
802.11
IEEE family of specifications for WLANs
2.4GHz 2Mb/s
Includes WEP
802.11a
5GHz, 54Mb/s
802.11b
Often called Wi-Fi, 2.4GHz, 11Mb/s
802.11e
QoS & Multimedia support to b & a
802.11g
2.4GHz, 54Mb/s
802.11i
An alternative of WEP, known as WPA2

3. Modes of WLANs Ad-Hoc Peer to Peer
Communication only to computers within transmission range
If communication to the internet is required then one of the members must act as a router
Called the Independent Basic Service Set (IBSS)

4. Modes of WLANs Infrastructure
Each client sends its data to an access point
The access points acts as a bridge and forwards the packets to other clients or to the wired network.
Called the Basic Service Set (BSS)

5. War Driving & Chalking People drive around looking for access points.
When an access point is found, a chalk mark is placed on the sidewalk or building

6. WEP WEP – Wired Equivalent Privacy
Supposed to give the same amount of privacy as a wired LAN
Used to prevent eavesdropping
Used to prevent unauthorized access to the LAN (not explicitly a goal of WEP)

7. Secure Protocols For Encryption
Application
Application
SSL
SSL
Transport
(TCP, UDP)
Transport
(TCP, UDP)
Router
Network (IP)
Network (IP)
Network (IP)
Network (IP)
(VPN)
(VPN)
802.11b Link
802.11b Link
Ethernet
Link
Ethernet
Link
WEP
WEP
802.1b
Physical
802.1b
Physical
Ethernet
Physical
Ethernet
Physical

8. Beacon Frame
Each access point broadcasts a beacon frame several times a second
It contains:
The beacon interval – How often does the frame get broadcast
A time stamp
Service Set Identifier (SSID)
Supported transmission rates
Parameter sets – frequency hops, delay, etc
Compatibility info – such as: all clients must use WEP
Traffic Map – What AP are in power saver mode

9. Probe Frame
A client may broadcast a probe frame to find the AP associated with an SSID.
The SSID is required for all communication with an access point.

10. Association
Before a client can communicate with the AP, a relation or association must be established.
There are 3 association states
1)Unauthorized and unassociated
2)Authenticated and unassociated
3)Authenticated and associated
To move from state1 to state 2 in an open system, a client sends a authentication request, and the AP responds with an authorization success frame.
Open systems may also employ MAC access lists to determine if the AP responds with an authorization success frame.

11. WEP Association WEP relies on a shared key
The client sends a authentication request indicating the use of a shared key
The AP responds with a challenge containing 128 Octets generated with the WEP pseudo-random number generator (PRNG) seeded with the shared key and an initialization vector (IV).
The client then encodes the message using the key, a new IV and sends it to the AP.
The AP decrypts and compares. This authenticates the client to the AP

12. WEP Uses an RC4 stream cipher Uses a shared key
Creates a repeatable stream of “random” data
The data is XORed with the data to get the encrypted data
Uses a shared key
Can be “64 bit or 128 bit”
Uses an initialization Vector (IV)
24 bit
Actually used as part of the key so…
The 64 bit key is actually a 40 bit shared key
The 128 bit key is actually a 104 bit shared key.
Increments with each frame (by convention)
Sent as clear text in each frame.

13. IP Data
ICV is a 32 bit CRC of the plain IP data
Seed RC4 with IV + shared key, XOR output with data
Hdr IV
Encrypted IP Data
ICV
IV Sent in clear text

14. Problems
Because of the XOR and the static shared key, getting two frames with the same IV one can statistically figure out the message.
Becomes even easier if you have multiple frames with the same IV
An AP sending out 1500byte packets at 11Mb/s will use every IV in about 5 hours. But most packets are smaller so the rollover will occur even sooner.
Most wireless cards reset their IV to 0 on reset.
Even worse…The standard makes changing the IV optional.
The ICV uses CRC32 which is good at detecting transmission problems, but easy to get a valid crc with altered data
Subject to replay attacks.

15. Attacks Passive Active
Listen to the air waiting for a duplicate IV and apply statistics.
Active
With knowledge of the contents (tcp/ip), the attacker can guess where the destination is, and by flipping some bits, the AP will send the packet to another address.
Once the attacker has the encrypted text and the decrypted text the XOR is easily gotten
Another active attack is to send a packet from the internet to a destination on the WLAN. The AP will encode the message, thus the attacker has both the encrypted and plan text again.

16. Defense Stop the AP from broadcasting the SSID
Change the SSID from the factory default
Don’t use any identifying number
Enable MAC authentication
Use 128 bit WEP
Change the default passwords on the AP itself
Set /change the shared key!!!
Place a firewall between the AP and the intranet
Use a higher level encryption such as SSL or VPN
Use WPA. This standard addresses these problems.

17. WPA WPA – Wi-Fi Protected Access
Designed to run with existing WEP access points with just a firmware change
Changes to WEP
TKIP (Temporal Key Integral Protocol)
48 Bit IV (instead of 24 bit)
At current a (54 Mb/s) it will take 645 years before the IV will roll
Initialized to 0 when the shared key is initialized
Increments with every packet sent out
AP rejects any packet with a IV less then the current count
Traffic halts if the key gets to it’s max value

18. WPA Changes to WEP TKIP (Temporal Key Integral Protocol) Shared Key TA
Change the per packet key with every association (instead of static)
Employ 802.1X EAPOL key message (RADIUS)
Use the transmitter’s MAC Address in the key (TA)
Shared Key TA IV
XOR
Shared Key
Phase 1 IV
RC4
Per Packet Key

19. WPA Changes to WEP Addition of a MIC (message Integrity Check)
Often referred to as Michael
A hash used to prevent message alteration
Hash the shared key, source address, destination address, and the data

20. WPA IP Data Seed RC4 with TKIP XOR output with data +IV 802.11 Hdr IV
+Source MAC
+Dest MAC
+Per packet Key
Seed RC4 with TKIP XOR output with data
+IV
Hdr IV
Encrypted IP Data IV
MIC
IV Sent in clear text
CRC32
Hdr IV
Encrypted IP Data
MIC
ICV

21. WPA Problems
If you know the type of packet (most likely ARP), the crc32 checksum will allow you to guess the bytes of the packet
Once you have a guess, you submit the packet to the AP. If the AP accepts the packet, you guessed the bytes correctly. Continue guessing.
WPA counter measure requires a 60 second delay between guesses
Using an ARP packet, you can generate your own ARP packets in about 12 minutes.
One you have ARP, you can do a man in the middle attack and see both the clear text and the encrypted text, and get the key stream, but…
You must use the QoS channel (if enabled) and then you can only send 15 packets before the IV changes the entire key stream.

22. WPA2 Fixes the WPA problems by only using a block cipher
Impossible to get a “key stream” as they don’t exist.
Problem: All packets are the increment of the block size! (multiples of 128 bit).
Uses AES –symmetric key, block cipher
Personal mode
Pre-shared key
Enterprise mode
Requires a pre-shared key
Uses 802.1x EAPOL key message (RADIUS) to generate a session key
Called a Robust Security Network (RSN)
Requires different hardware then WPA equipment
RSN is incompatible with WPA