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Imagine a Wi-Fi network protected by WEP/WPA/WPA2. Users can join the network in case they know the pre-shared key of the access point.

Is it possible for a user A (who has successfully logged into the network) to sniff on the data communication of another user B, entirely because A uses the same pre-shared key like B (and C, D, E....)?

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  • $\begingroup$ possible duplicate of If the PSK is known, is it possible to decrypt traffic from other clients in a WPA2 wlan network? $\endgroup$ – poncho Mar 28 '12 at 20:30
  • $\begingroup$ Note that this isn't precisely a duplicate, because he asks about WEP/WPA as well (which actually have a different answer than WPA2) $\endgroup$ – poncho Mar 28 '12 at 20:35
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    $\begingroup$ This might functionally be answered by this question on security? $\endgroup$ – user46 Mar 28 '12 at 21:43
  • $\begingroup$ Thank you two very much for your competent answers. Now I'm a little shocked regarding security in Wi-Fi networks even when using WPA2. Is there a way to circumvent this flaw? For instance, consider the use case where a Wi-Fi user does not want other Wi-Fi users to know which websites he is accessing. $\endgroup$ – Abdull Mar 29 '12 at 14:00
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Well, it depends on the which protocol is being used.

For WEP and WPA, the keys used are derived directly from the pre-shared keys; that means that as long as you know the pre-shared keys, you can immediately decrypt packets as well.

On the other hand, WPA2 is somewhat stronger; the two sides exchange nonces to derive the keys. Hence, unless you listen into the initial exchange, you're out of luck. On the other hand, depending on when you start listening, this might not be that great of an improvement.

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    $\begingroup$ When I've looked into wifi hacking, it sounds like a pretty common technique is to DoS the client over the air until it drops and reconnects. I believe this allows the attacker to observe the nonces exchanged at the initial handshake. $\endgroup$ – Marsh Ray Mar 29 '12 at 15:43

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