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WPA (Key management (Key Hierarchy in 802.11 (The final level is Per…
WPA
Key management
Key Hierarchy in 802.11
The next level is the Pair-wise Transient Keys (PTK) which is derived from the PMK
The final level is Per-Packet Keys
generated by key-mixing function
Use IV incremented by one for each packet as input in two phases
use PTK as input
At the top level is the Pair-wise Master Key (PMK)
Environments
Home network
Manual configuration (pre-share key)
Enterprise network
802.1X key establishment
Confidentiality
Temporal Key Integrity Protocol (TKIP) encryption
Us 48-bit initialization vector
Use 104-bit per-packet keys, different for each packet
Authentication
Use 802.1X authentication framework
Architecture
Authenticator
Supplicant
Authentication server
Procedure
Before authentication, the supplicant only allowed access to the AS
After authentication, the supplicant granted access to network resources by the AP
Authentication occurs after association
Use
Extensible Authentication Protocol(EPA)
Handle authentication requests
Remote Authentication Dial-in User Service (RADIUS)
Handle secure signalling between AP and AS
Integrity checking
Use MICHAEL
Relies on shift and add operations
Not secure as other standardized MIC protocols
Take countermeasure by requiring that each STA start using an IV=0 then increment the value by one for each packet
Protection against replay attacks
Use 48-bit TKIP sequence counter (TSC) to generate IV and
avoid replay attack.