3.4
- Hirte attack against WEP encryption
- The
Hirte attack extends the Caffe-Latte attack using fragmentation
techniques. As the same way that with Caffe-Latte attack, there is no
need of AP in the viccinity for the Hirte attack to be launched,
being enough a WEP client isolated from the legitimate AP.
- Fragmentation
attacks use the fact that the first 8 bytes of the encrypted packet
consist of the Link Layer Control (LLC) header. Because this is sent
into plaintext, the attacker can XOR it with the encrypted packet,
achieving the first 8 bytes of the RC4 keystream, and using this
keystream along with the matching IV to create encrypted packets.
However, the amount of data it can fit into 8 bytes is only 4 bytes
because the last 4 bytes are devoted to the WEP ICV. Fragmentation
helps to send a maximum of 16 fragments per packet, allowing to send
a packet of reassembled size 64 bytes. This fact will be used to
inject packets like ARP request and replies.
- The
Hirte attack sniffs an ARP packet and relocates the IP address in the
ARP header to convert the reassembled packet into an ARP request for
the wireless client. The client responds with an ARP reply, allowing
the attacker to gather new data packets encrypted with the WEP key.
Once enough number of packets are gathered, aircrack-ng can
crack the WEP key rapidly.
- For
this practice, the lab set is exactly the same that at previous
Caffe-Latte attack. Now, the command airbase-ng uses the
option -N to specify the Hirte attack, instead of the option -L for
Caffe-Latte.
- After
the legitimate AP is unplug, the client "roch" connects to
the created fake aP by the attacker "kali". Only 1 minute
later than the association,at 21:55:13, the Hirte attack is started
up:
- Airodump-ng
detects the association between the victim "roch" and the
fake AP, writing the captured packets to the file Hirte-WEP:
- The
file hirteWEP-01.cap and its derivatives are created:
- As
usual, aircrack-ng finds the WEP key
A8925DC44A5432DE814CE109F9 after no much time:
