Jacob Bertels
Christopher Rawlings
What is a Wireless Network?
Basic network is WLAN
-
Wireless LAN
Most based on the IEEE 802.11 standards
Use IP and MAC address
WPAN
–
Wireless Personal Area Network
Bluetooth
Infrared Data
Association (IrDA)
Near Field
Communication
More Wireless Networks
WWAN
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Wireless Wide Area Network
Mobile Telecommunications cellular network
LTE, Uses Encryption and Authentication
Point
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to
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point and Omnidirectional
Cellular Networks
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Towers
Different Frequencies
Cell phones
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Tower Handoff
Signal
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to
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Noise
Wireless Mesh Networks
Mesh Topography of Routers
Usually Fixed mesh routers
form a multi
-
hop structure of a
network
Can be modeled as a graph
Edge would be: Distance, Data
Rate, Noise, Frequency
Mesh is “self
-
healing”
Mesh Network Cont.
Load Balancing Priority over Shortest Path
Measures current congestion on each path
Continually runs algorithm
Better Approach To Mobile
Adhoc
Networking (B.A.T.M.A.N.)
Detects other nodes, informs neighbors
Sends out , node remembers direction
Cares only about the best first step
Dynamically creates routes
Data Packet Scheduling
Minimize resource starvation and make fair
Some Routers and switches use First
-
In
-
First
-
Out (FIFO)
-
Based in a Queue
Round Robin
Separate Queue for every data flow
Algorithm lets each data flow to take turns
Can use Weight Round Robin for Priorities
Error Correction
Forward Error Correction
Encodes Redundancy for Verification at
Receiver
Simple FEC
-
(3,1) repetition code (inefficient)
Repetition of same byte multiple times
Parity Bits are used
Sets the last bit (odd or
even number of 1s)
Hamming(7,4)
Error Correction Cont.
Multidimensional Parity
-
Check Code
Ex. Want to send: 2541
Split up into 25, 41, add parity
Goes to 257,415, add digits 66
Send code 25741566
-
Decoder receives
value
Error Correction Cont.
Turbo Code
-
Used for 3G and Satellite
Encoder
-
Takes input converts to three outputs
Interleaver
scrambles input into pseudo
-
random pattern
Redundancy is added in each Encoder
Multiple outputs ensures consistency
Error Correction Cont.
Turbo Code
-
Decoder
Decoder tries to decode each input
Uses feedback and iteratively verifies
data is correct
What is WEP?
Wired Equivalent Privacy
First
Wifi
encryption standard
Uses stream cipher RC4
Two Key sizes
64bit
128bit
How WEP Encryption Works
Start with a Key
Make a pseudo
random Initialization
vector
Concatenate the Key
with the Initialization
Vector(IV) to make a
Keystream
The
Keystream
is then
XOR’ed
with the plain
text
data
Encrypted
Data
Collecting Data
Generating Traffic
Collecting Data
Password Broken
What is WPA?
Wi
-
Fi Protected Access
Used as a time filler until WPA2 ratified
WPA Strengths
Still used RC4 cipher, but increased the
IV length to 48 bits
Also used a different
keystream
for each
packet
Began salting the key with the network
name
Causes computation time to increase
WPA Flaws
Small packets such as ARP packets or
DNS packets are crack
-
able
Still very difficult because of key size
What is WPA2?
Wi
-
Fi Protected Access II
Also called Full IEEE 802.11i or IEEE
802.11.i
-
2004
○
But who really wants to remember that
Current top of the line wireless security
WPA2 Strengths
Very Large Key
256 bits
Uses AES algorithm
Not a stream Cipher
Based on 4x4 Matrices
Not going to go into much detail
○
Don’t want to steal another group’s topic too
much
WPA2 Weakness
Only one major weakness
Not even in the algorithms
WPS Flaw
Wi
-
Fi Protected Setup
Allows easy secure network connectivity
Has a pin made up of 8 numbers
○
Grouped in 2 groups 4&4
If an attacker can break the pin, they can get
the encryption key without breaking the
crypto
Breaking WPA
Must capture “4 way handshake”
Only real way is to brute force the
password
You must have a list of “words” to try as
passwords
Can have a list of words ready for
attacking or have a program that makes
the words on the fly
Capture 4
W
ay Handshake
Brute Forcing Password
Password Found
Breaking WPA
You can pre
-
compute the hashes
Rainbow tables(hash tables)
○
Contain the hash and the corresponding key
○
They still have to be computed, but they can
be computer beforehand and kept
○
Church of
Wifi
rainbow tables ~45GB
1000 top network names
~
1,000,000 passwords
Breaking WPA
Either way, if a complex password is
used, breaking the password becomes
mathematically impossible
Breaking WPA Example
64 character password
94 possible characters(full keyboard)
Possible passwords=7.33x10^126
@
1googolplex(10^100/s
)
passwords/second
On average to brute force it would take
1.16*10^19=11600000000000000
YEARS!
Questions?
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