There are well known attacks to WPA by capturing handshake and running offline hashcracking against it. Also there are tools to exploit vulnerability in WPS to get the PIN. My question is why WPS handshake (if it is called handshake) cannot be captured and the PIN revealed. It seems impossible otherwise obviously someone had done it already.

1 Answer 1


A Diffie-Hellman key exchange occurs before exchanging the sensitive information. Please see https://www.grc.com/sn/sn-338.htm . The relevant part:

"But it absolutely will encrypt the dialogue so that somebody just capturing the packet traffic is unable to, as I said last week, get the data, take it home, and crack the PIN offline. That can't happen because the dialogue is protected by this initial establishment of a secret key which doesn't authenticate, but it does give them privacy."

So cracking the 'handshake' as you call it (it isn't really a handshake), would be much much more complex than just performing a brute-force attack against the PIN, as this 'handshake' is encrypted with strong asymmetric encryption.

  • So even before PIN exchange they already have shared secret. But then it is vulnerable to man in the middle attacks right ? Jun 2, 2014 at 19:56
  • Diffie Hellman is vulnerable to MITM, but not the way you think. It is a bit too complex to explain, but basically the two parties 'create' their public-private keypair on the fly. There is NO shared secret that is exchanged; the shared secret is created. Of course, a MITM could intercept the messages used for this 'creation'. Explanation of Diffie Hellman: security.stackexchange.com/questions/58658/… Explanation of Diffie Hellman MITM vulnerability: stackoverflow.com/questions/9953187/…
    – Michael
    Jun 3, 2014 at 8:17
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    Yes I understand diffie hellman. I mean theoretically you could intercept the dialog between AP and client and make a DH exchange with both parties. But in practice it seems not easy since you cant prevent radio waves reaching other party. With some kind of jammer maybe? Anyways thanks for clearing it for me. Jun 3, 2014 at 10:09
  • Ok I understood your comment incorrectly. So what you mean is that you setup a rogue AP, and that you ask clients to connect through a WPS pin. I guess that would be possible, theoretically. I have no references to a practical implementation of that, though.
    – Michael
    Jun 3, 2014 at 10:27
  • @user3155036 Theoretically it should be possible, but your device must be on during the handshake. Is it realistic? Jul 11, 2017 at 17:01

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