You can add decryption keys using Wireshark's Up to 64 keys are supported. You should see a window that looks like this: Click on the "Edit This may not work for captures taken in busy environments, since the last-seen SSID may not be correct. Click on the Decryption Keys As shown in the window you can select between three decryption modes: None , Wireshark , and Driver : Selecting None disables decryption.
Selecting Wireshark uses Wireshark's built-in decryption features. Driver will pass the keys on to the AirPcap adapter so that Driver mode only supports WEP keys. Gotchas Along with decryption keys there are other preference settings that affect decryption. Worse still, the The first attack follows directly from the above observation. A passive eavesdropper can intercept all wireless traffic, until an IV collision occurs. The resulting XOR can be used to infer data about the contents of the two messages.
IP traffic is often very predictable and includes a lot of redundancy. This redundancy can be used to eliminate many possibilities for the contents of messages. Further educated guesses about the contents of one or both of the messages can be used to statistically reduce the space of possible messages, and in some cases it is possible to determine the exact contents. When such statistical analysis is inconclusive based on only two messages, the attacker can look for more collisions of the same IV.
With only a small factor in the amount of time necessary, it is possible to recover a modest number of messages encrypted with the same key stream, and the success rate of statistical analysis grows quickly. Once it is possible to recover the entire plaintext for one of the messages, the plaintext for all other messages with the same IV follows directly, since all the pairwise XORs are known.
An extension to this attack uses a host somewhere on the Internet to send traffic from the outside to a host on the wireless network installation. The contents of such traffic will be known to the attacker, yielding known plaintext. When the attacker intercepts the encrypted version of his message sent over The following attack is also a direct consequence of the problems described in the previous section. Suppose an attacker knows the exact plaintext for one encrypted message.
He can use this knowledge to construct correct encrypted packets. The procedure involves constructing a new message, calculating the CRC, and performing bit flips on the original encrypted message to change the plaintext to the new message. This packet can now be sent to the access point or mobile station, and it will be accepted as a valid packet.
A slight modification to this attack makes it much more insidious. Even without complete knowledge of the packet, it is possible to flip selected bits in a message and successfully adjust the encrypted CRC as described in the previous section , to obtain a correct encrypted version of a modified packet.
If the attacker has partial knowledge of the contents of a packet, he can intercept it and perform selective modification on it. For example, it is possible to alter commands that are sent to the shell over a telnet session, or interactions with a file server.
The previous attack can be extended further to decrypt arbitrary traffic. In this case, the attacker makes a guess about not the contents, but rather the headers of a packet. This information is usually quite easy to obtain or guess; in particular, all that is necessary to guess is the destination IP address. Armed with this knowledge, the attacker can flip appropriate bits to transform the destination IP address to send the packet to a machine he controls, somewhere in the Internet, and transmit it using a rogue mobile station.
Most wireless installations have Internet connectivity; the packet will be successfully decrypted by the access point and forwarded unencrypted through appropriate gateways and routers to the attacker's machine, revealing the plaintext. If a guess can be made about the TCP headers of the packet, it may even be possible to change the destination port on the packet to be port 80, which will allow it to be forwarded through most firewalls.
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