Transcript Analysis of the WEP Protocol - Brigham Young University

MD5 Cracking
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One way hash.
Used in online passwords and file
verification.
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Lets destroy an MD5 hash
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Lets use “steiner”
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Md5('steiner')=
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7bfd4d773bec1249bb691bbad9d968a8
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Input into rcrack.
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./rcrack *.rt -h 7bfd4d773bec1249bb691bbad9d968a8
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Wait
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MD5 hashing
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Tables vary greatly in size.
Each added character add's exponential
growth
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md5_loweralpha-numeric_1-8
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36.4 GB
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General Wireless
Vulnerabilities
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Invasion and resource stealing
Traffic redirection
Denial of service
Rogue access points
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The Wired Equivalent Privacy Protocol
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Goals
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Confidentiality
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Access control
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Prevent casual eavesdropping
Protect access to network infrastructure
Data integrity
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Prevent tampering with transmitted messages
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Logistics
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A key is shared between the client and
access point
Key length is 40 bits or 104 bits
Keys are static and whenever a key
changes, all clients must update
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RC4 Stream Cipher
Key
Plain Text
RC4 Key
Setup
Pseudo Random
Number
Generator
XOR
Cipher Text
Key Stream
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WEP Implementation of RC4
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Checksum of the plain text is computed
to provide data integrity
24 bit Initialization vector (IV) is used to
increase the size of the secret key
IV also makes it harder to crack by
changing the key stream every time
IV is pre-pended to the cipher text, that
way client can decrypt the message
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Encryption Process
Integrity Check
Algorithm
Plain Text
Plain Text
IV
ICV
Key
XOR
RC4
IV
Cipher Text
Key Stream
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Decryption Process
Key
IV
RC4
Cipher Text
XOR
Integrity Check
Algorithm
Plain Text
ICV
Plain Text
Key Stream
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WEP Authentication
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Client sends message to access point
(AP) requesting authentication
AP sends plain text stream to client
Client chooses IV and encrypts plain
text stream
Client sends IV and cipher text to AP
for verification
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WEP Frame
WEP Frame
802.11
Header
IV
Key
Payload
Number
ICV
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WEP Flaws and Exploits
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Database Attack
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Some access points allow traffic to be
encrypted or unencrypted
Hacker sends packets to the access point
broadcast messages, AP responds with
encrypted version
Hacker records key stream and puts it in
database for later use
When client gets sent message with IV that is
in the database, hacker XORs the two to get
the plain text
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Key Scheduling Attack
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Some IVs are weak and through
statistical analysis can reveal
information about the key
Active attack involves de-authenticating
client repeatedly until enough packets
have been received to analyze
Utilizes the fact that several bytes of IP
traffic can be easily predicted
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Message Injection
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Hacker can listen to authentication
process and determine a key stream for
a particular IV
Using this key stream, hacker can
create packets and inject them into the
network
WEP allows for IVs to be reused
without triggering an alarm
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WEP Cracking Tools
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Linux Security Distributions
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Several live CDs are available that
contain all tools necessary to hack
WEP
Common applications include:
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Aircrack Suite
- wesside-ng
- aireplay-ng
- aircrack-ng
Airsnort
Kismet
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How to Protect Against and Attack
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Newer Security Protocols
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Stop using WEP and use a newer
protocol like WPA
Make you password harder to crack by
using the maximum number of
characters and using random ASCII
characters ***(deprecated)***
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Authentication
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Evil Twin Attack
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Hacker can force user off the AP, then use the
same SSID to pose as the AP
How do you know who has control of
an access point?
Enterprise systems can use a server to
authenticate users
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Other Suggestions
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Wireless IDS
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Can monitor network to prevent rogue access
points
If attacker attempts to break into wireless
LAN, the IDS can triangulate his location
Use end to end encryption
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VPNs
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Demo
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Locate target
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Do research
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Get AP MAC and client MAC
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Input into wesside-ng
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If necessary, spoof a clients MAC
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Lan Manager (LM) Hashes
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Used by Microsoft
Windows passwords are stored using this
algorithm
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Only hashes 7 characters at a time.
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Makes cracking considerably easier
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Lets break my windows
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Get Hash
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Input into ophcrack
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wait
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