Re: Cracking WEP and WPA keys

[Demetrio Carrión <demetrio.carrion () gmail com>]

Hi,

The key is not sent to the AP in the clear. The WEP authentication is
a challenge-response protocol.

1. The AP sends a 128bit number (challenge)
2. The client/user encrypts the challenge with the WEP key (Challenge XOR Key)
3. The AP compares the client response against the expected response.
4. The AP sends an ACK or NACK response

You can brute force the response, since you have the challenge and
might end up discovering the key. You don't need to set up a fake AP
to carry out this type of attack, although.

Regards,

Demetrio Carrión

On 12/14/05, pagvac <unknown.pentester () gmail com> wrote:
> Would the following attack be feasible for obtaining a WEP key?
>
> Set up an AP with VERY strong signal and same SSID as the one used by
> the target network. After that, the client should be able to attempt
> to connect to your AP (you send stronger signal than the legitimate
> one) and send you the WEP which you could sniff from the AP itself.
>
> After that you're done and the key is yours.
>
> Am I talking non-sense here? Wouldn't the WEP key be sent to the AP in
> the *clear* at the beginning of the handshake? Otherwise how can the
> AP check whether or not the client is using the right key?
>
> I've never tested this and my assumptions might be based on incomplete
> and inaccurate knowledge about how wi-fi technologies.
>
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--
Demetrio de Souza Diaz Carrión
Mestrando em Redes de Computadores COPPE/UFRJ
Engenheiro Eletrônico UFRJ

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