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Enhancing Wireless Security with WPA

CS-265 ProjectSection: 2 (11:30 – 12:20)

Shefali Jariwala

Student ID001790660

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Agenda

Overview of WLAN WEP and its weaknesses Promise of WPA

- Modes of Operations- Security Mechanisms

What is WPA2? Encryption Method Comparison Table Conclusions

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WLAN Standards• 802.11 1-2 Mbps speed 2.4 GHz band• 802.11a (Wi-Fi) 54 Mbps speed 5 GHz band• 802.11b (Wi-Fi) 11 Mbps speed 2.4 GHz band• 802.11g (Wi-Fi) 54 Mbps speed 2.4 GHz band

WLAN components• Wireless Clients• Access Points

Requirements for secure WLAN• Encryption and Data Privacy• Authentication and Access Control

Overview of WLAN

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Security Mechanism – Wired Equivalent Privacy

• Confidentiality, Access Control and Data Integrity

• Both WEP Authentication and encryption are based on a secret key shared between AP and wireless client

• WEP uses RC4 encryption algorithm

Symmetric Key stream Cipher variable length key 64 bit = 40 bit WEP key and 24 bit random number known as IV to encrypt the data

Encryption: stream cipher plaintext = cipher text Sender sends the packet = cipher text + IV to receiver Decryption: WEP key and attached IV

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WEP Encryption

WLAN security: Current and Future, Park, J.S; Dicoi, D.; IEEE Internet Computing, Volume:7, Issue:5, Sept-Oct, 2003, 60-65

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Two modes of authentication:

Open System ( “No Authentication”) Shared Key

WEP Authentication

Client Access Point

Authentication request Random challenge

Encrypted RC

Success/failure response

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A single key is used for all AP’s and wireless clients

Static WEP key ~ Dynamic WEP Key

Same key used for Access Control and Encryption which gives rise to problems

Initialization Vector (IV) Reuse Ci = Pi ksi and Ci’= Pi’ ksi’

Therefore, Ci Ci’= Pi Pi’

Known Plain text attacks

WEP provides no replay protection

When WEP was available it was not always turned on

WEP Weaknesses

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stronger security solution via standards-based interoperable security specification known as WPA (Wi-Fi specification)

WPA is a subset of 802.11i standard and maintains forward compatibility

Run as software upgrade on AP’s and NIC’s and minimizes the impact of network performance

Inexpensive in terms of cost/time to implement and addresses all WEP weaknesses

Secure all versions of 802.11 devices including 802.11b, 802.11a and 802.11g

Promise of WPA - Wireless Protected Access

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Enterprise Mode:

- Requires an authentication server – RADIUS (Remote Authentication Dial In Service) for authentication and key distribution

- RADIUS has centralized management of user credentials

Pre-shared key (PSK) Mode:

- Does not require authentication server

- A “shared secret” is used for authentication to access point

- vulnerable to dictionary attacks

WPA - Modes of Operation

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Enterprise Mode Diagram

http://www.wi-fi.org/opensection/pdf/whitepaper_wi-fi_security4-29-03.pdf

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PSK Mode Diagram

http://www.wi-fi.org/opensection/pdf/whitepaper_wi-fi_security4-29-03.pdf

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Needed if no authentication server is in use

“shared secret” – revealed, network security is compromised

No standardized way of changing shared secret

It increases the attacker’s effort to do decryption of messages

The more complex the shared secret is, the better it is as there are less chances of dictionary attacks

Issues of PSK Mode

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Security Mechanisms in WPA

http://www.intel.com/ebusiness/pdf/wireless/intel/wpa_cmt_security.pdf

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802.1X Authentication prevents end users from accessing Enterprise networks

http://www.mtghouse.com/MDC_WP_052603.pdf

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Simpler Representation

Authenticator(Access Point)

Initiates connection

Supplicant(Wireless Client)

Port = enabledState = unauthorizedrequests identity

responds with identity

Response ACCEPT/REJECT

Supplicant’sPort = enabledState = authorized

Forwards the identity

Forwards Response

requests identity from RADIUS Forwards the request

RADIUS passes its identity

Access points forwards the identity

RADIUS

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Mutual Authentication

http://www.mtghouse.com/MDC_WP_052603.pdf

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TKIP is responsible for generating the encryption key, encrypting the message and verifying its integrity TKIP ensures: - Encryption key changes with every packet - Encryption key is unique for every client - TKIP encryptions keys are 256 bit long WEP Encryption key = shared secret + IV TKIP packet comprises of: - 128 bit temporal key (shared by both clients and AP) - Client Device MAC address - 48 bit IV (Packet sequence number) to prevent known plain text attacks (WEP = 24 bit IV)

TKIP – Temporal Key Integrity Protocol

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TKIP key mixing function + temporal key = per packet key

Temporal keys - 128 bit, change frequently, definite life

MAC Address + Temporal key + four most significant octets of the packet sequence number are fed into the S-Box to generate intermediate key

Results in a unique encryption key

Then, mix the intermediate key with two least significant octets of packet sequence number = 128 bit per packet key

Each key encrypts only one packet of data and prevents weak key attacks

TKIP for Data Privacy

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Used to enforce data integrity

“Message Integrity Code” (MIC) = 64 bit message calc. using Michael’s algorithm

MIC is inserted in the TKIP packet

The sender and the receiver each compute MIC and then compare. MIC does not match = data is manipulated

Detects potential packet content altercation due to transmission error or purposeful manipulation

Uses 64 bit key and partitions the data into 32 bit blocks

Various operations: shifts, XOR’s, additions

Michael Message Integrity Check

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WEP vs. WPA

http://www.wi-fi.org/opensection/pdf/whitepaper_wi-fi_security4-29-03.pdf

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Vulnerable to Denial-of-Service Attacks

AP receives 2 data packets that fail MIC check within 60 seconds - active attack

Counter measure for AP’s which includes disassociating each client using the AP

Prevents the attacker from getting encryption keys

Users can loose network connectivity for 60 seconds

Drawbacks of WPA

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Uses the Advanced Encryption Standard (AES)

Symmetric key block 128 bit key

Full 802.11i support including Counter Mode with CBC- MAC Protocol (CCMP) encryption

CCMP = CTR + CBC + MAC

Will require or replacement hardware (AP’s and NIC’s)

Certified Equipments due in late 2004

Upcoming WPA2

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Encryption Method Comparison Table

WEP WPA WPA2

Cipher RC4 RC4 AES

Key Size 40 bits128 bits encryption 64

bits authentication128 bits

Key Life 24 bit IV 48 bit IV 48 bit IV

Packet Key Concatenated Mixing Function Not needed

Data Integrity CRC-32 Michael Algorithm CCM

Header Integrity None Michael Algorithm CCM

Replay Attack None IV Sequence IV Sequence

Key Management None EAP Based EAP Based

http://www.wi-fi.org/opensection/pdf/Wi-Fi_ProtectedAccessWebcast_2003.pdf

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WEP is not secure anymore !

WPA solves almost all WEP weaknesses

WPA still considered secure and provides secure authentication, encryption and access control

WPA is not yet broken…!

WPA2 is a stronger cipher than WPA and will provide robust security for WLANs

Conclusions

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References

WLAN security: Current and Future, Park, J.S; Dicoi, D.; IEEE Internet Computing, Volume:7, Issue:5, Sept-Oct, 2003, 60-65

Wireless networking security: Security flaws in 802.11 data link protocols, Nancy Cam-Winget, Russ Housley, David Wagner, Jesse Walker; Communications of the ACM-Volume 46, Issue 5 (May 2003), Pages 35-39

http://www.cizgi.com.tr/makaleler/seminer/S2-1.pdf

http://www.dtm.ca/download/wireless_toshiba.pdf

http://www.intel.com/ebusiness/pdf/wireless/intel/wpa_cmt_security.pdf

http://www.mtghouse.com/MDC_WP_052603.pdf

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http://www.sans.org/rr/papers/68/1109.pdf

http://www.sans.org/rr/papers/68/1301.pdf

http://www.wi-fi.org/opensection/pdf/whitepaper_wi-fi_security4-29-03.pdf

http://www.wi-fi.org/opensection/pdf/Wi- Fi_ProtectedAccessWebcast_2003.pdf

http://www.hackfaq.org/wireless-networks/wpa-wi-fi-protected-access.shtml

http://techrepublic.com.com/5100-6265-5060773.html

References