The WEP decapsulation is pictorially depicted below
FIG Courtesy: 802.11 Standard
WEP follows the below procedure to decrypt the received 802.11 WEP encrypted frame.
- WEP extracts the initialization vector (IV) and Key ID from the received packet to obtain the relevant WEP key. If Key-mapping keys are used, then the Key-mapping key will be used and the Key ID ignored
- WEP decryption engine creates the key-stream and applies the key-stream (Exclusive OR) on the encrypted packet to obtain the plain-text MPDU
- The ICV is recomputed and compared with the ICV concatenated in the MPDU. If the ICV mismatches – the frame is dropped and an indication is provided to the upper layer as decrypt error