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IEEE 802.11 WEP(Wired Equivalent Privacy) Concepts and Vulnerability
ByShivu Vibhuti
[email protected] -Spring 2005
Advisor : Dr. Mark [email protected]
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Agenda
What is WEP?
WEP Design objectives
WEP Authentication
WEP Encryption/Decryption
WEP Vulnerability & attacks
How to strengthen wireless security
Q&A
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What is WEP (Wired Equivalent Privacy)?Protection mechanism offered by the IEEE 802.11 standard
Operates on the Media Access Control (MAC) layer
Aim is to provide data privacy equivalent to the level of wired network
WEP algorithm is used to protect wireless communication from eavesdropping
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Design Objectives as per the IEEE 802.11 standard
It is reasonably strong
It is self-synchronizing
It is efficient
It may be exportable
It is optional
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WEP Design objectives
It was not designed to be the ultimate "killer" security feature
The intention was to make it hard to break-in
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WEP Open Authentication
Based on request and grant
Essentially no authentication i.e. no client validation
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WEP Shared Key Authentication
Based on request, challenge, challenge-response, grant/deny
Worse than open system authentication, exposes keystream
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Shared Key Authentication Vulnerability
Known keystream can be used to generate response
Response = (Challenge) XOR (known keystream for a particular IV)
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Shared Key Authentication Vulnerability...
Same shared key is used for both authentication and encryption
Prone to man in the middle attack
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WEP Encryption
Based on symmetric shared key encryption, uses RC4 stream cipher
PlainText PlainText CRC
XOR
IV RC4 Keystream
Ciphertext CiphertextIV
Secret Key
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WEP Decryption
CiphertextIV IV Secret Key
KeystreamXOR
Ciphertext
CRCPlaintext
Plaintext
CRC
CRC
Compare
Good Data
Bad Data
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WEP VulnerabilityIV mechanism has made the protocol vulnerable
The IEEE 802.11 does not specify how to generate IV's
Uses 40 or 104 bits key with 24 bits IV
RC4 keystream repeats if IV's are repeated, major flaw in the WEP design/implementation
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WEP VulnerabilityAttacker can identify when IV collision occurs
Attacker can pick two packets derived from the same key and obtain the unknown plaintext using C1 XOR C2 = P1 XOR P2
Same IV can be used with every packet
Cannot differentiate between forged packets and the original packets
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WEP VulnerabilityDifficult to keep secret, when the same key is shared among multiple users/devices
Same key is used for a long time
CRC checksum failed to protect data integrity
Fluhrer, Mantin and Shamir discovered a flaw in the WEP key scheduling algorithm(IV weakness)
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WEP attacks
Known plaintext attack
Reaction attack – Guess some of the bits in a message & determine the other bits
Inductive attack – Trial and Error
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WEP attacksInductive attack – trial and error method
Obtain initial keystream K (length n)
Create ICMP ping or ARP request packet
Choose packet length to be “n+1”, attacker knows n bytes K, for n+1 th byte, try 256 different values
AP discards incorrect packet and responds to the correct packet, attacker now knows n+1 bytes of keystream
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WEP cracking tools
AirSnort
WEPCrack
Dweputils
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Strengthening Wireless Security
Choose bigger IV
Use different mechanisms for the data integrity check For example: Hash functions
keys can be assigned per user and configured to be changed based on time or packet limits
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Strengthening Wireless Security
Make wireless network invisible i.e. Drop-ping unencrypted packets/requests
Use different authentication protocols e.g. EAP, LEAP, PEAP
Use alternative protocols
IEEE 802.11i and TKIP, WPA, WPA in Pre-Shared Key (PSK) mode
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ConclusionDon't just rely on WEP security, take ad-ditional measures at the higher layer
WEP has many weaknesses due to the small IV space and poor selection of CRC32 for data integrity verification
Another major issue with WEP is the key scheduling algorithm flaws discovered by Fluhrer, Mantin and Shamir
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IEEE 802.11 WEP(Wired Equivalent Privacy) Concepts and Vulnerability
Q&A
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Thank You!