6.3 For WEP, data integrity and data confidentiality are achieved using the RC4 stream encryption algorithm. The transmitter of an MPDU performs the following steps, referred to as encapsulation: 1. The transmitter selects an initial vector (IV) value. 2. The IV value is concatenated with the WEP key shared by transmitter and receiver to form the seed, or key input, to RC4. 3. A 32-bit cyclic redundancy check (CRC) is computed over all the bits of the MAC data field and appended to the data field. The CRC is a common error-detection code used in data link control protocols. In this case, the CRC serves as a integrity check value (ICV). 4. The result of step 3 is encrypted using RC4 to form the ciphertext block. 5. The plaintext IV is prepended to the ciphertext block to form the encapsulated MPDU for transmission. a. Draw a block diagram that illustrates the encapsulation process. b. Describe the steps at the receiver end to recover the plaintext and perform the integrity check. c. Draw a block diagram that illustrates part b. | |
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