1. Wireless Network Security Issues By Advait Kothare SJSU CS265 Fall 2004

2. Introduction A presentation of the paper “Your 802.11 Wireless Network has No Clothes” by – William A. Arbaugh,Narendra Shankar,Y.C. Justin Wan at Univ. Maryland at College Park Explosive growth in wireless networks. But many security issues initially left open by 802.11 standards committee. Result : weak or non-existent security solutions for current deployments.

3. Introduction (Cont.) In the Wired World emphasis on protection from external compromise. (Firewalls) Wireless Networks provide an access point for any adversary beyond physical controls. A “back door” is opened for an attacker, which can be exploited. (Parking lot attacks) And a simple eavesdropping attack against 802.11 shared key authentication.

4. Standard Security Mechanisms Wired Equivalent Privacy protocol (WEP) – For confidentiality of network traffic – Demostrated to be vulnerable Open Systems Authentication – Authenticates anyone who requests authentication – Management frames sent in clear even with WEP Shared Key Authentication – Uses a standard challenge and response protocol

5. Shared Key Authentication InitiatorResponder Authentication Request Seq # 1 Authentication Challenge Seq # 2 Authentication Response Seq # 3 Authentication Result Seq # 4

6. Shared Key Authentication (Cont.) Initator sends an authentication req. management frame Responder replies by sending mgmt. Frame with 128 octets of challenge text. – Text Generated using WEP PRNG with shared secret and a random initialization vector (IV) Initiator copies the text into a new frame, encrypts with WEP using shared secret and a new IV Responder verifies text and 32-bit CRC (ICV)

7. Weaknesses in Shared Key Auth. Passive attack, eavesdropping 1 leg of auth. Works because fixed structure of protocol Random challenge is the only diffrence between two Authentication messages. Also because of weakeness in WEP WEP = Pseudo Random Number Generator K = Shared key IV = Initialization Vector (Sent in clear) P = Plain text challenge text C = Cipher text R = Challenge text

8. Shared Key Auth. (Cont) Messages based on sequence numbers Sequence #Status CodeChallenge Text WEP Used 1ReservedNot PresentNO 2StatusPresentNO 3ReservedPresentYES 4StatusNot PresentNO

9. Shared Key Flaw (Cont.) Attacker captures 2 nd & 3 rd frames. – 2 nd Frame => Random challenge in clear (P) – 3 rd Frame => Encrypted challenge (C) PRNG stream – WEP K,IV P R = C P – Stream can be derived from above without knowing the shared Key (K)

10. Shared Key Attack Attacker requests authentication from an AP AP responds with challenge text (R) in clear Attacker takes R and PRNG to get valid authentication response by XOR-ing the 2 Attacker computes a new integrity check value (ICV) Valid response allows Attacker to join the network.

11. Conclusions & Future Work All deployed 802.11 networks are at risk WEP can make it harder but vulnerable as keys are static and hard to change Vendors have used un-authenticated Diffie- Hellman for key exchange. Worse solution as Man In The Middle attack can give the Key to the attacker.

12. Question & Comments