WEP

WEP was proposed to provide link-level security for 802/;11 netowrks
Its intended security goals wer confidentiality, access control, integrity and authentication

WEP uses a shared secret key for encrypting and authenticating data between a wireless client and the access point
one of four shared keys can be manually configured in the AP and the wireless clients
some wireless cards rotate the key used amoing the four keys periodically
lkeys use 40 bits or 104? bits

WEP encryption:

24-bit IV, 40 or 104 bit secret key → (concat) → 64 bit or 128 bit WEP key → Peudo random generator → key stream

802.11 data frame → CRC → integrity check value (IV) → (concat with original frame)

XOR with key stream to get ciphertext.

24-bit IV is sent with the ciphertext.

WEP decryption:

24 bit IV and ciphertext are sent over
24-bit IV + 40/104 bit secret key → (concat) → WEP key → PSG → key stream
ciphertext XORd with key stream

product an 802.11 fram and an ICV2. perform CRC on the 802.11 frame and check if it matches the ICV2.

[client] [Access point]
auth req →
← challegne text
encrypted challenge response
→
← auth response

Weaknesses in WEP:

1. Shared secret key: same key for all clients.
2. Static key: Key does not change unless manually done.
3. IV is sent in plaintext: This means the actual keysize is either 40 or 104 bits, not 64 or 128 bits.
4. Size of the IV is only 24 bits: This means IVs are repeated.
Let C1 = P1 (+) PNG(k, IV1) where p1 = plaintext, c1=ciphertext, k=secretkey.
Let C2 = P2 (+) PNG(k, IV2)
If IV1=IV2 = IV
C1 (+) C2 = P1 (+) PNG(k, IV) (+) P2 (+) PNG(k, IV)
C1 (+) C2 = P1 (+) P2
This can help in reverse engineering the key.
5. Use of CRC as a message digest algorithm is weak.
6. Authentication reveals a plaintext/ciphertext pair.
7. One-way authentication: Client does not challenge the access point.
8. Management frames are not encrypted.

Index