Cryptography Reference
In-Depth Information
Alice
Bob
Generate IV
Compute ICV
IV || E IV || K ( data || ICV )
Form IV || K
and decrypt
Verify ICV
Figure 12.3. WEP encryption process
Alice:
1. generates a 24-bit pseudorandom initialisation vector IV and appends the
WEP key K to IV to form the key:
K = IV || K ;
2. computes a 32-bit CRC checksum ICV of the data, and appends this to the
data;
3. encrypts the data plus ICV using key K ;
4. sends IV (in the clear) and the resulting ciphertext to Bob.
Bob then:
1. appends the WEP key K to the received IV to form the key K ;
2. decrypts the ciphertext using K and extracts the checksum ICV ;
3. verifies that the checksum ICV is correct.
If the verification of ICV is successful then Bob accepts the data packet.
ENTITY AUTHENTICATION IN WEP
The WEP entity authentication technique is very simple. It is based on the same
challenge-response principle that we first discussed for dynamic passwords in
Section 8.5 and that was used in several of the protocols analysed in Section 9.4.
If Alice (a device) wants to identify herself to Bob (a wireless access point):
1. Alice sends a request to authenticate to Bob;
2. Bob sends a nonce r B to Alice;
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