Wireless Security Rick Anderson Pat Demko

Wireless Medium Open medium Broadcast in every direction Anyone within range can listen in No Privacy Weak Authentication

a,b,g –Standards do not require security –All use same encryption mechanisms Short range, low power environment Supported by many devices

Common Encryption Methods WEP –Wired Equivalent Privacy –Ratified in 1999 –Commonly used in home routers, commercial applications WPA –Wi-Fi Protected Access –Tries to improve upon WEP weaknesses i (WPA 2)

The Effects of Encryption Raises computational time –Increases power consumed by devices Adds additional overhead –Decreases overall throughput

WEP Data link level Uses a shared Secret Key Stream cipher RC4 for confidentiality –Ensures info is given to only those who are authorized CRC-32 checksum for integrity –Ensures the validity of the data transmitted

WEP, cont. Uses 2 key sizes –40 bit –104 bit Each key has a 24 bit Initialization Vector (IV) –Random number used to synchronize encryption –Transmitted in the clear

WEP Weaknesses Doesn’t include a key management protocol –Relies upon a single shared key Shared Key Easily Cracked –RC4 has a large amount of weak keys By knowing a small amount of bits, you can determine a large amount of the remaining bits easily. –Passive Attacks to decrypt traffic –Active Attacks to insert traffic

WEP Weaknesses Data headers remain unencrypted –Anyone can see source, dest. address Weak integrity check –Payload can be modified and the CRC can be updated without knowing the WEP key.

Exploiting WEP AirSNORT Once 5-10 million packets have been gathered, < 1 second to crack WEP Crack –Open source tool to exploit same RC4 vulnerabilities

WPA Wi-Fi Protected Access Created to patch WEP Intended as intermediate security platform –Between WEP and i formalization

WPA Designed to be used with 802.1X authentication server –Distributes different keys to each user Can be used without the server in less secure pre-shared key mode Data encrypted with RC4 with 128 bit key –48 bit IV

WPA Temporal Key Integrity Protocol (TKIP) –Major improvement over WEP –Dynamically changes key as system is used –Combined with larger IV, this defeats well known attacks Improved payload integrity vs. WEP –Uses more secure message integrity check (MIC) known as Michael

WPA Message Integrity Check (Michael) –Includes a frame counter to prevent replay attacks Fixes problem with undetected modification attacks The strongest algorithm WPA makers could devise that worked with most network cards Still subject to attack To limit risk, WPA networks shut down whenever an attempted attack is detected

WPA Weaknesses Fundamentally much harder to crack Weakness still lies in the key –Possible to passively intercept initial key exchange messages then use an offline dictionary attack to find password Could allow DoS attacks

802.11i Also known as WPA 2 WPA addressed problems with WEP, but still had room for improvement i is still being formalized Implements new encryption algorithm –No use of RC4

802.11i Uses Advanced Encryption Standard algorithm (AES) –Variable key sizes of 128, 192 and 256 bits –Much harder to decrypt than WPA or WEP Not compatible with today’s devices –Requires new chip sets

Other ways to secure a Wireless Network MAC filtering –Easy to spoof a MAC address Using another authentication method –Force users to authenticate using a username/password VPN tunnel between computer and AP

Weakness in Key Scheduling Algorithm of RC4